In conclusion, there were notable differences for the total lean tissue mass between the non-walkers and walkers. Nonwalkers displayed significantly lower segmental lean mass of the trunk, arms, and legs, resulting in significant differences in total body mass between groups. The regression equations developed from able-bodied populations using BMI, waist circumference, age, and skinfold thickness measurements substantially underestimated body fat content, particularly in non-walkers. All formulae, apart from that of Lean et al.'s (1996) in the walkers, showed significant differences between the equation outcomes and DXA-derived body fat percentage, with an underestimation in body fat percentage and large systematic errors across present in all equations (ranging from 8 to 14%). Due the strong correlation between sum of 8 skinfold thickness and body fat percentage, and the low SEE for walkers and non-walkers, this variable could be suitable to establish future impairment specific regression equations for wheelchair game players.

### REFERENCES

#### ACKNOWLEDGMENTS

The research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. With thanks to the participants of the GB wheelchair basketball and rugby squads and Diane Harper for assisting with the DXA-scans and Dr. John Lenton with the skinfold measurements.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2015 Willems, Paulson, Keil, Brooke-Wavell and Goosey-Tolfrey. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# Differences in Left Ventricular Global Function and Mechanics in Paralympic Athletes with Cervical and Thoracic Spinal Cord Injuries

Katharine D. Currie1 , Christopher R. West 1, 2 and Andrei V. Krassioukov 1, 3, 4 \*

1 Autonomic Research Laboratory, International Collaboration on Repair Discoveries, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada, 2 Translational Integrative Physiology Laboratory, Faculty of Education, School of Kinesiology, University of British Columbia, Vancouver, BC, Canada, 3 Division of Physical Medicine and Rehabilitation, Faculty of Medicine, University of British Columbia, Vancouver, BC, Canada, 4 GF Strong Rehabilitation Centre, Vancouver Coastal Health, Vancouver, BC, Canada

Following a spinal cord injury, there are changes in resting stroke volume (SV) and its response to exercise. The purpose of the following study was to characterize resting left ventricular structure, function, and mechanics in Paralympic athletes with tetraplegia (TETRA) and paraplegia (PARA) in an attempt to understand whether the alterations in SV are attributable to inherent dysfunction in the left ventricle. This retrospective study compared Paralympic athletes with a traumatic, chronic (>1 year post-injury), motor-complete spinal cord injury (American Spinal Injury Association Impairment Scale A-B). Eight male TETRA wheelchair rugby players (34 ± 5 years, C5-C7) and eight male PARA alpine skiers (35 ± 5 years, T4-L3) were included in the study. Echocardiography was performed in the left lateral decubitus position and indices of left ventricular structure, global diastolic and systolic function, and mechanics were derived from the average across three cardiac cycles. Blood pressure was measured in the supine and seated positions. All results are presented as TETRA vs. PARA. There was no difference in left ventricular dimensions between TETRA and PARA. Additionally, indices of global diastolic function were similar between groups including isovolumetric relaxation time, early (E) and late (A) transmitral filling velocities and their ratio (E/A). While ejection fraction was similar between TETRA and PARA (59 ± 4 % vs. 61 ± 7 %, p = 0.394), there was evidence of reduced global systolic function in TETRA including lower SV (62 ± 9 ml vs. 71 ± 6 ml, p = 0.016) and cardiac output (3.5 ± 0.6 L/min vs. 5.0 ± 0.9 L/min, p = 0.002). Despite this observation, several indices of systolic and diastolic mechanics were maintained in TETRA but attenuted in PARA including circumferential strain at the level of the papillary muscle (−23 ± 4% vs. −15 ± 6%, p = 0.010) and apex (−36 ± 10% vs. −23 ± 5%, p = 0.010) and their corresponding diastolic strain rates (papillary: 1.90 0.63 s ± −1 vs. 1.20 ± 0.51 s−1 , p = 0.028; apex: 3.03 ± 0.71 s−1 vs. 1.99 ± 0.69 s −1 , p = 0.009). All blood pressures were lower in TETRA. The absence of an association between reduced global systolic function and mechanical dysfunction in either TETRA or PARA suggests any reductions in SV are likely attributed to impaired loading rather than inherent left ventricular dysfunction.

Keywords: athletes, echocardiography, paraplegia, strain, stroke volume, tetraplegia

#### Edited by:

Gregoire P. Millet, University of Lausanne, Switzerland

#### Reviewed by:

Pierre-Marie Leprêtre, Université de Picardie Jules Verne, France Stefanos Volianitis, Aalborg University, Denmark

> \*Correspondence: Andrei V. Krassioukov<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Exercise Physiology, a section of the journal Frontiers in Physiology

Received: 11 September 2015 Accepted: 07 March 2016 Published: 29 March 2016

#### Citation:

Currie KD, West CR and Krassioukov AV (2016) Differences in Left Ventricular Global Function and Mechanics in Paralympic Athletes with Cervical and Thoracic Spinal Cord Injuries. Front. Physiol. 7:110. doi: 10.3389/fphys.2016.00110

# INTRODUCTION

The classification of Paralympic athletes is sports specific and considers physical, visual and/or intellectual impairments. Typically athletes with a spinal cord injury (SCI) are competing against individuals with a similar lesion level (i.e., cervical or thoracic SCI). However, there are sporting competitions where individuals with cervical and thoracic SCI are competing against each other, in addition to other non-SCI athletes. The consideration of how the lesion level may influence exercise performance is therefore necessary to ensuring fair competition between the diverse population of Paralympic athletes.

One contributing factor to exercise performance is the capacity of the cardiovascular system to adequately respond to the body's demands. This includes the responses of the heart, vasculature, and adrenal medulla. Following SCI, there are lesion level dependent alterations in how the cardiovascular system responds to an exercise stimulus. While sympathetic preganglionic neurons originate in the thoracic and upper lumbar segments of the spinal cord (T1-L2), sympathetic innervation of target organs is segmental. Innervation of the heart and vascular smooth muscle of the upper body arise from the high thoracic segments (T1-T5), while innervation of the vascular smooth muscle of the lower body and adrenal medulla arise from the lower thoracic and lumbar segments (T6-L2). Cervical SCI results in the most dramatic alterations in cardiovascular outcomes at rest and in response to exercise, due to the disruption of descending sympathetic input to target organs below the level of injury (Krassioukov, 2009). We recently confirmed this by demonstrating individuals with tetraplegia who had an autonomic complete SCI also reached attenuated peak heart rates of 102 ± 34 bpm while individuals with tetraplegia and autonomic incomplete SCI reached higher peak heart rates (161 ± 20 bpm) (Currie et al., 2015). Additional cardiovascular responses that are attenuated during exercise in individuals with tetraplegia include the changes in blood pressure (Thijssen et al., 2009), catecholamine levels (Schmid et al., 1998a,b), and stroke volume (SV) (Kessler et al., 1986; Hostettler et al., 2012). Contrary to tetraplegia, individuals with high and low paraplegia have either partial or full preservation of descending sympathetic pathways to the heart, vascular smooth muscle and adrenal medulla, and therefore are capable of mounting an appropriate cardiovascular response during exercise. Previous research has demonstrated individuals with paraplegia are capable of reaching peak heart rates in range of their age-predicted heart rate maximum (Hopman et al., 1992, 1993; Jacobs et al., 2002) and display exercise-induced increases in circulating catecholamines (Schmid et al., 1998a,b) and blood pressure (Dela et al., 2003; Claydon et al., 2006). SV responses to aerobic exercise in individuals with paraplegia, however, are inconclusive with previous research either demonstrating no change (Davis and Shephard, 1988; Hopman et al., 1993; Raymond et al., 2001; Theisen et al., 2001) or small increases (Davis et al., 1987; Hopman et al., 1992; Raymond et al., 1999). Overall, exerciseinduced increases in cardiac output (Q˙ ) in individuals with SCI are primarily driven by changes in heart rate, with individuals

Altered SV responses in SCI have primarily been attributed to a reduction in loading (i.e., decreased venous return) (Theisen, 2012). However, no studies have examined whether factors inherent to the left ventricle (LV) per se are also a contributing factor. Echocardiographic assessments of LV mechanics are a non-invasive tool that may help to determine if changes in LV performance following SCI are associated with SV reductions. Indices of LV mechanics include strain (ε) and strain rates (SR) which assess the degree and rate of myocardial deformation in longitudinal, radial and circumferential axes; rotation (Rot) and rotation rates (RotR) of the base and apex of the LV; and overall LV twist and twisting/untwisting rates (Voigt et al., 2015). In clinical conditions, such as chronic heart failure, there is a concomitant reduction in global LV systolic function [SV; LV ejection fraction (EF)] and LV systolic mechanics (Leung and Ng, 2010; Ma et al., 2014), and recent evidence suggests lower ε in these patients is associated with a reduced exercise capacity (Hasselberg et al., 2015). Additionally, indices of LV mechanics are sensitive to increases and decreases in sympathetic activity (Weidemann et al., 2002; Akagawa et al., 2007), which may provide insight into the influence of lesion level on LV performance. Few studies have performed echocardiographic assessments in athletes with SCI (Huonker et al., 1998; Gates et al., 2002; Schumacher et al., 2009; Maggioni et al., 2012; West et al., 2012a; De Rossi et al., 2014), with none of these investigations examining LV mechanics. Given evidence that global LV systolic dysfunction is associated with impairments in LV mechanics, and that these functional changes may limit exercise performance, the examination of LV structure, function and mechanics in athletes with SCI may help to elucidate potential factors limiting cardiac responses to exercise. Therefore, the purpose of this study was to compare resting LV structure, function and mechanics in high-performance athletes with SCI.

# MATERIALS AND METHODS

## Participants

This was a retrospective comparison of echocardiography data collected at both summer and winter Paralympic events. Inclusion criteria included males between 18-60 years of age who had sustained a chronic (>1 year post-injury), motorcomplete [American Spinal Injury Association Impairment Scale (AIS) A-B], traumatic SCI, and who have been competing at the international level for at least 3 years. Eight Paralympic wheelchair rugby players with a cervical SCI (TETRA) and eight Paralympic alpine skiers with a thoracic SCI (PARA) met the criteria and were included in the study. The neurological level of injury and AIS was confirmed using the International Standards for Neurological Classification of SCI (Kirshblum et al., 2011). Exclusion criteria for the study included any history of cardiovascular disease or acute illness/infection, which was confirmed with a verbal medical history, and any language or cognitive barrier that prevented the participant from following English instructions. The International Paralympics Committee, University of British Columbia Clinical Research Ethics Board, and Brunel University Research Ethics Board approved all protocols, which conformed to the Declaration of Helsinki, and all individuals provided written informed consent prior to participation. Prior to testing, participants were instructed to abstain from food and drink for 4 h, alcohol and caffeine for 12 h, and exercise for 24 h. On the day of testing, all participants were instructed to void their bladder to reduce the potential influence of sympathetic reflex activation on blood pressure.

#### Blood Pressure Assessments

Blood pressures were measured from the left brachial artery using an automated machine (Dinamap Pro 300 V2; GE Healthcare, Milwaukee, USA). Seated and supine measurements were collected in duplicate following 5 and 10 min of quiet rest, respectively.

#### LV Assessments

Cardiac images were collected with the participants in the left lateral decubitus position using two-dimensional echocardiography (Vivid 7; GE Healthcare, Horton, Norway) according to the recommendations of the American Society for Echocardiography (Quiñones et al., 2002; Lang et al., 2005; Voigt et al., 2015). Heart rate was measured continuously using a single-lead electrocardiogram. Images were analyzed offline using dedicated software (EchoPAC; GE Healthcare, Horten, Norway) by a single blinded investigator, and the average of three cardiac cycles is presented.

Indices of LV structure were measured at end-diastole (d) and end-systole (s) from the parasternal long axis view, including LV internal diameter (LVID), and interventricular septal wall (SWT), and posterior wall (PWT) thickness. Relative wall thickness (RWT) was calculated as [(2 × PWTd)/LVIDd]. LV mass (LVMI) was calculated according to an established formula (Devereux et al., 1986), and indexed to body surface area (Du Bois and Du Bois, 1989). Modified single-plane Simpson's method was used to analyze apical four-chamber views to determine end-diastolic (EDV) and end-systolic (ESV) volumes, and the global systolic function outcomes of SV, EF, and Q˙ which was calculated as the product of SV and heart rate. Global diastolic function outcomes were determined from pulsed-wave Doppler at the tips of the mitral valve leaflet. Outcomes included early (E) and late (A) transmitral filling velocities and their ratio (E/A), and isovolumetric relaxation time (IVRT).

Indices of LV mechanics were derived from 2D speckletracking analysis of apical four-chamber and parasternal short axis images at the level of the mitral valve (basal), papillary muscle (mid), and apex (apical) using established guidelines (Mor-Avi et al., 2011). Using a cubic spline algorithm, raw speckle-tracking traces were interpolated by customized post-processing software (2D Strain Analysis Tool, Stuttgart, Germany) into 600 points in systole and 600 points in diastole to control for heart rate differences. Peak ε and SR in systole and diastole were determined from short-axis (radial, circumferential) and four-chamber (longitudinal) images. Peak Rot and RotR in systole and diastole were determine at the basal and apical levels, and twist was determined as the maximum value from subtracting frame-by-frame basal and apical Rot data. Peak systolic twisting velocity and early diastolic untwisting velocity were determined the same way using frame-by-frame basal and apical RotR data.

### Statistical Analyses

Statistical analyses were performed using Statistical Package for Social Science software (IBM Corporation, Armonk, NY, USA). Data were assessed for normality using Shapiro-Wilk tests and Q-Q plot analyses. Between group differences were determined using independent t-tests and Mann-Whitney U-tests for normally and non-normally distributed data, respectively. Effect sizes were calculated using Cohen's d. Data are presented as mean ± SD unless otherwise noted, with P < 0.05 considered statistically significant.

## RESULTS

Individual and group values for participant characteristics are presented in **Table 1**. Body surface area was similar in TETRA (1.84 ± 0.13 m2 ) and PARA (1.93 ± 0.15 m2 , p = 0.232). Selfreported training history was available in 5 of 8 TETRA and all 8 PARA athletes. There was no significant difference in the number of years competing at an international level (TETRA: 11 ± 4 years; PARA: 8 ± 5 years, p = 0.275) or weekly training volume (TETRA: 10 ± 3 hours/week; PARA: 16 ± 13 hours/week, p = 0.192). For seated and supine hemodynamics, heart rates were

A, motor- and sensory-complete; AIS, American Spinal Injury Association Impairment Scale; B, motor-complete and sensory-incomplete; C, cervical; L, lumbar; T, thoracic; TPI, time post-injury.

similar between groups while all blood pressure values were lower in TETRA compared to PARA (**Figure 1**).

Indices of LV structure and global function are presented in **Table 2**. Structure and global diastolic function was similar between groups, while global systolic function was reduced in TETRA compared to PARA including slower heart rates and smaller SV and Q˙ . Indices of LV mechanics are presented in **Table 3**. Basal Rot and RotR in both systole and diastole were higher in TETRA. The TETRA group also presented with higher circumferentialε(**Figure 2**) and diastolic SR at the mid and apical levels compared to PARA.

#### DISCUSSION

This is the first study to examine the influence of lesion level on resting LV structure, function and mechanics in Paralympic athletes with SCI. We observed no difference in LV dimensions or global diastolic function, while global systolic function was reduced in TETRA compared with PARA. Despite these observations, there were no indicators of LV mechanical dysfunction in the TETRA group, while PARA presented with attenuated systolic and diastolic mechanics. This observation may suggest a training induced improvement in mechanical efficiency in PARA that would increase their capacity to respond during an exercise bout.

The athletes included in this retrospective study were from two distinct sporting events. While we would consider any Paralympic athlete as highly trained, the nature of the training regiments for wheelchair rugby and alpine skiing are unique and incorporate different amounts of endurance and resistance exercise. While there is evidence in the able-bodied literature that endurance and resistance exercise training elicit differential cardiac adaptations (Spence et al., 2011), evidence from a cross-sectional examination of athletes with paraplegia found no differences in LV dimensions or global LV function between power-trained and endurance-trained athletes (Gates et al., 2002). Furthermore, endurance and resistance training in individuals with paraplegia has been shown to elicit similar improvements in peak oxygen uptake (Jacobs, 2009). Thus, it is unlikely that the differences observed between the TETRA and PARA groups are attributed to the differences in training modality. Both groups had similar weekly volumes of exercise training, and had been engaging in international competition for a similar duration. Additionally, the global LV indices observed in PARA athletes are comparable to values recently reported by De Rossi et al. (2014) in their examination of endurance trained athletes with paraplegia (i.e., wheelchair basketball, handball and tennis). While the training regiments for wheelchair rugby and alpine skiing are different, they do incorporate both aerobic and resistance exercises, which based on the literature to date, do not appear to elicit specific cardiac adaptations in individuals with SCI.

Exercise training may exert differential effects on global LV function depending on lesion level. De Rossi et al. (2014) demonstrated increased global diastolic function in athletes with tetraplegia and paraplegia relative to their sedentary peers with tetraplegia and paraplegia. However, SV was reduced in both sedentary and athletic groups with tetraplegia and only improved in athletes with paraplegia relative to sedentary individuals with paraplegia. Findings from the present study are in support of lesion level dependent differences in global function. We observed no difference in global diastolic function

Currie et al. Ventricular Mechanics in SCI Paralympians

Data are mean ± SD. A, late transmitral filling velocity; d, end-diastolic; E, early transmitral filling velocity; EDV, end-diastolic volume; EF, ejection fraction; ESV, end-systolic volume; IVRT, isovolumetric relaxation time; LVID, left ventricular internal diameter; LVM, left ventricular mass; PWT, posterior wall thickness Q, cardiac output; RWT, relative wall ˙ thickness; s, end-systolic; SV, stroke volume; SWT, septal wall thickness. Bolded values in P-value column indicate significant between-group differences.

between TETRA and PARA, while SV and Q˙ were lower in TETRA compared to PARA. The reduction in SV and subsequently Q˙ are likely attributed to a smaller EDV given ESV was similar between groups, which implies reduced cardiac filling was likely responsible for the attenuated SV. LV dimensions were similar between groups; therefore the observed reduction in EDV is unlikely attributed to a smaller ventricle. While no investigations have directly compared LV dimensions between TETRA and PARA athletes, Kessler et al. (1986) observed smaller dimensions in sedentary individuals with tetraplegia compared to sedentary individuals with paraplegia. A more recent investigation using a pooled sample of athletes with tetraplegia and paraplegia observed no difference in LV dimensions when compared to able-bodied individuals and larger dimensions when compared to sedentary individuals with tetraplegia and paraplegia (De Rossi et al., 2014). Therefore, our observation of similar dimensions between the two groups is not unusual, and is likely attributed to the training status of our sample.

Contrary to the global systolic indices, systolic mechanics appear to be higher in TETRA relative to PARA. This includes

Data are mean ± SD. c, circumferential; ε, strain; l, longitudinal; r, radial; Rot, rotation; RotR, rotation rate; SR, strain rate. Bolded values in P-value column indicate significant between-group differences.

higher basal Rot and circumferential ε at the level of the papillary muscle and apex, and a faster basal RotR. The ε-values reported in our TETRA sample are similar to values reported in the able-bodied literature (Yingchoncharoen et al., 2013). It is, therefore, unlikely that systolic mechanics are enhanced in the TETRA group, but rather the values in PARA group are lower. Head-down bed rest, which typically mirrors the

cardiac adaptations following SCI, has been shown to elicit a reduction in SV, ε and systolic SR in able-bodied individuals (Kozakova et al., 2011; Scott et al., 2014). The observation of preserved systolic mechanics and reduced SV in TETRA was therefore unanticipated, and may be attributed to their hemodynamic state. In particular, reductions in afterload have been shown to increase systolic mechanics (Burns et al., 2010); therefore the lower blood pressure in our TETRA group may have created an environment where systolic mechanics can be maintained despite reductions in loading. Hypotension has consistently been demonstrated in sedentary (West et al., 2012b) and athletic (West et al., 2014) individuals with tetraplegia, and is attributed to the disruption of descending sympathetic input to the vasculature.

The observation of lower systolic and diastolic mechanics in our PARA group may be indicative of two scenarios: LV dysfunction/disease or a "resetting" of resting mechanics. Lower resting LV mechanics have been documented in clinical populations (Leung and Ng, 2010); however, we believe our finding is not pathological since global LV diastolic and systolic function (E/A and EF) were in a normal range (Lang et al., 2005; Dalen et al., 2010). The "resetting" of LV mechanics to lower resting values have been observed in high performance able-bodied athletes (Richand et al., 2007; Nottin et al., 2008), and while the mechanisms behind this adaptation are presently unknown, it is believed to create a large range for cardiovascular adjustments during exercise (Nottin et al., 2008). Both systolic and diastolic mechanics are increased during exercise in ablebodied individuals (Notomi et al., 2008; Stohr et al., 2011; Lee et al., 2012; Hensel et al., 2014). In addition to the obvious association between elevations in SV and ε, the augmentation of diastolic mechanics during exercise is key to promoting efficient diastolic filling, which in turn supports the elevations in SV (Notomi et al., 2008). It is presently unknown if exercise training in individuals with SCI elicits similar changes in LV mechanics as high-performance able-bodied athletes. Given cross-sectional evidence that athletes with paraplegia experience more favorable LV adaptations than athletes with tetraplegia (De Rossi et al., 2014), we postulate that involvement in highperformance sports and its associated large volume of exercise training may be capable of modifying LV mechanics to a lower resting value in PARA. Whether this modification has any impact on LV performance during exercise remains to be determined since LV performance per se has never been investigated during exercise post-SCI. Indeed, the few studies that have investigated the cardiac response to exercise in SCI have focused on measures of SV and report conflicting results, with some studies reporting increases in SV during armexercise (Davis et al., 1987; Hopman et al., 1992; Raymond et al., 1999), and others reporting no change (Davis and Shephard, 1988; Hopman et al., 1993, 1998; Raymond et al., 1999, 2001; Theisen et al., 2001). The discrepancy in these observations may be attributed to differences in the method used to estimate SV (ex. CO2 rebreathing, echocardiography, or impedance cardiography) and the acute exercise protocol (submaximal vs. maximal arm exercise). Nevertheless, the absence of apparent LV mechanical dysfunction at rest in high-performance athletes with SCI in the present study suggests any abnormal SV responses during exercise are likely attributable to reduced loading.

# LIMITATIONS

The absence of an able-bodied control group makes it difficult to draw conclusions regarding the direction of the LV mechanics. While global LV outcomes suggest the PARA group is free from LV dysfunction, it is possible that the attenuated LV mechanics values are indicative of impending cardiac dysfunction. Conversely, the TETRA group may have experienced an "enhancement" of LV mechanics to accommodate the cardiovascular requirements of their endurance sport. In order to fully understand the influence of lesion level of LV mechanics in Paralympic athletes, future research should attempt to evaluate athletes in similar sporting events, especially sports in which TETRA and PARA athletes are in competition against each other (ex. wheelchair basketball or Para-cycling team relays).

# CONCLUSION

In conclusion, high-performance athletes with TETRA and PARA experience differential changes in LV indices. While we would speculate these changes are attributed to lesion level, they may also be influenced by their training modality. TETRA athletes can be characterized as having normal diastolic function but reduced systolic function, an observation likely attributed to impaired venous return. On the other hand, PARA athletes demonstrated lower values for LV mechanics yet had no evidence of global systolic or diastolic dysfunction. We speculate this observation may be attributed to training induced improvements in LV efficiency rather than indicative of inherent LV dysfunction.

# AUTHOR CONTRIBUTIONS

KC—Conception of the work; data acquisition, analysis and interpretation; drafting and revising manuscript; approved final copy; and agrees to be accountable. CW—Conception of the work; data acquisition and interpretation; critically revised manuscript; approved final copy; and agrees to be accountable. AK—Conception of the work; data acquisition and interpretation; revising manuscript; approved final copy; and agrees to be accountable.

# REFERENCES

# FUNDING

Research at the Paralympic events was supported by donations from the International Collaboration on Repair Discoveries, Coloplast, Wellspect HealthCare, and the Shkreli Foundation. Dr. KC was supported by a Craig H. Neilsen Foundation Postdoctoral Fellowship (281863).

# ACKNOWLEDGMENTS

The authors would like to thank the athletes for taking the time to participate in our study, and GE Healthcare for generously lending us an ultrasound during field-testing. We would also like to acknowledge the International Paralympics Committee for providing us the opportunity to perform field-based assessments of Paralympic athletes.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2016 Currie, West and Krassioukov. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# Perspective: Does Laboratory-Based Maximal Incremental Exercise Testing Elicit Maximum Physiological Responses in Highly-Trained Athletes with Cervical Spinal Cord Injury?

Christopher R. West 1, 2, 3 \*, Christof A. Leicht 4 , Victoria L. Goosey-Tolfrey 4 and Lee M. Romer 3

1 International Collaboration on Repair Discoveries, University of British Columbia, Vancouver, BC, Canada, 2 School of Kinesiology, University of British Columbia, Vancouver, BC, Canada, 3 Centre for Sports Medicine and Human Performance, Brunel University London, London, UK, 4 School of Sport, Exercise and Health Sciences, The Peter Harrison Centre for Disability Sport, Loughborough University, Loughborough, UK

#### Edited by:

Olivier Girard, University of Lausanne, Switzerland

#### Reviewed by:

Can Ozan Tan, Harvard Medical School, USA Masaki Mizuno, University of Texas Southwestern Medical Center, USA Pierre-Marie Leprêtre, Université de Picardie Jules Verne, France

> \*Correspondence: Christopher R. West<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Exercise Physiology, a section of the journal Frontiers in Physiology

Received: 29 August 2015 Accepted: 21 December 2015 Published: 14 January 2016

#### Citation:

West CR, Leicht CA, Goosey-Tolfrey VL and Romer LM (2016) Perspective: Does Laboratory-Based Maximal Incremental Exercise Testing Elicit Maximum Physiological Responses in Highly-Trained Athletes with Cervical Spinal Cord Injury? Front. Physiol. 6:419. doi: 10.3389/fphys.2015.00419 The physiological assessment of highly-trained athletes is a cornerstone of many scientific support programs. In the present article, we provide original data followed by our perspective on the topic of laboratory-based incremental exercise testing in elite athletes with cervical spinal cord injury. We retrospectively reviewed our data on Great Britain Wheelchair Rugby athletes collected during the last two Paralympic cycles. We extracted and compared peak cardiometabolic (heart rate and blood lactate) responses between a standard laboratory-based incremental exercise test on a treadmill and two different maximal field tests (4 min and 40 min maximal push). In the nine athletes studied, both field tests elicited higher peak responses than the laboratory-based test. The present data imply that laboratory-based incremental protocols preclude the attainment of true peak cardiometabolic responses. This may be due to the different locomotor patterns required to sustain wheelchair propulsion during treadmill exercise or that maximal incremental treadmill protocols only require individuals to exercise at or near maximal exhaustion for a relatively short period of time. We acknowledge that both field- and laboratory-based testing have respective merits and pitfalls and suggest that the choice of test be dictated by the question at hand: if true peak responses are required then field-based testing is warranted, whereas laboratory-based testing may be more appropriate for obtaining cardiometabolic responses across a range of standardized exercise intensities.

Keywords: field tests, aerobic exercise, tetraplegia, cardiovascular system

# INTRODUCTION

With the advancement of the Paralympic movement over the last 10–20 years the physiological monitoring of Paralympic athletes, including maximal aerobic and anaerobic exercise testing in both the field and laboratory, is now common practice (Goosey-Tolfrey, 2010). Technological advances in treadmill and wheelchair roller design permit externally valid assessments of physiological parameters during wheelchair propulsion under carefully controlled laboratory conditions. The majority of studies that have assessed maximal exercise responses of elite athletes with cervical spinal cord injury (SCI) during wheelchair propulsion on a treadmill, including our own, have reported peak oxygen uptake values in the range of 0.8–1.6 L/min and maximal heart rate (HR) values in the range of 100–140 bpm, although the mean is typically around 120 bpm (Coutts et al., 1983; Wicks et al., 1983; Lasko-McCarthey and Davis, 1991; Schmid et al., 1998; Leicht et al., 2013; Paulson et al., 2013; West et al., 2014a). The dogmatic pathophysiological explanation for these relatively low values is purported to be loss of descending sympathetic cardiac control along with an attenuated catecholamine response and a decreased active muscle mass (Figoni, 1993; Hopman et al., 1998).

Recently, we reported that field-based exercise testing in elite wheelchair rugby athletes with cervical SCI elicits HR values of 140–180 bpm (West et al., 2014b). These values far exceed those collected in the same athletes during armcrank ergometry and wheelchair propulsion on a treadmill (West et al., 2013). Further investigation revealed that a large number of these elite tetraplegic athletes (both rugby and handcycling) exhibit sparing of descending sympathetic fibers in the face of a motor and sensory compete injury (i.e., autonomic incomplete injury; Currie et al., 2015). Thus, it appears that factors other than disrupted descending sympathetic control may preclude the attainment of true peak physiological responses in the laboratory. To date, no study has specifically compared peak cardiometabolic responses between maximal field- and laboratory-based wheelchair exercise tests in highly-trained athletes with cervical SCI.

We have been collecting physiological data leading into the Beijing and London Paralympic cycles on the Great Britain wheelchair rugby squad. During this time, we have conducted a variety of field- and laboratory-based exercise tests on the same group of athletes, but have never directly compared peak physiological variables between laboratory- and field-based maximal wheelchair exercise tests. In the present study, we retrospectively reviewed our data and compared peak physiological responses between a standard incremental laboratory-based wheelchair treadmill test and two different field testing protocols.

# MATERIALS AND METHODS

#### Data Included

Nine male wheelchair rugby athletes with motor complete traumatic cervical SCI (C6-C7; 28.6 ± 2.6 year, 71 ± 16 kg, 1.80 ± 0.10 m, 7.1 ± 3.7 year post injury) were included into the study. The data were part of other research studies, some of which have been published elsewhere (8 of the present participants' 4 min push data, West et al., 2014b, and 8 of the present participants' maximal incremental test data Leicht et al., 2013; West et al., 2014a). All of the studies were approved by the University research ethics committee. In addition to peak physiological values, we extracted participant demographics and their International Wheelchair Rugby Federation (IWRF) classifications at the time of testing.

# Study Design

Data were extracted for three different maximal exercise trials. Trial 1 consisted of a maximal 4 min field-based exercise test on a 110 m long indoor athletics track with a wide turnaround area at each end. Trial 2 (n = 7) consisted of a maximal 40 min field-based exercise test in a sports hall. Trial 3 consisted of an incremental wheelchair propulsion test on a treadmill. Athletes were thoroughly familiar with the testing protocols. Each trial was completed with athletes exercising in their own rugby wheelchair with regular strapping and gloves. Prior to each trial, athletes received the same standardized pre-test instructions, namely to void their bladder to minimize the chance of autonomic dysreflexia, and to avoid strenuous exercise for 24 h, caffeine for 4 h and food for 2 h prior to assessment. Trials 1 and 3 were performed between 1 and 8 months apart. Trial 3 was performed approximately 1 month after trial 2.

# Experimental Trials

#### Trial 1

Athletes completed a maximal 4 min push on a 110 m synthetic indoor running track with minimal rolling resistance. Athletes pushed maximally in a straight line and were only required to turn at each end of the track where a wide area was provided to facilitate the maintenance of high speeds. Athletes were encouraged to cover as much distance as they could during 4 min. Environmental temperature ranged from 18.2 to 19.4◦C, humidity from 40 to 42%, and barometric pressure from 737 to 739 mmHg.

#### Trial 2

Athletes completed a maximal 40 min push around a large sports hall. The push consisted of: a straight 40 m push along the first side, a 30 m zigzag push along the second side, a straight 40 m push along the third side and a 30 m backwards zigzag push along the final side. The athletes were encouraged to cover as much distance as possible during 40 min.

#### Trial 3

Athletes completed a maximal incremental wheelchair test to volitional exhaustion on a motorized treadmill with a moving rail to prevent falls (Saturn 300/125r, HP Cosmos, Nussdorf-Traunstein, Germany). Treadmill speed was kept constant and ranged from 2.0 to 2.8 m·s −1 , depending on IWRF classification and previous performance during incremental treadmill exercise. The gradient was set at 1% and was increased gradually by 0.1–0.2% every 40 s. The maximal test was terminated when athletes were unable to maintain the treadmill speed, i.e., when they touched the spring of the safety rail for a third time. Standardized verbal encouragement was given throughout the test and push rate was freely chosen. All athletes underwent a standardized warm up as described elsewhere (Leicht et al., 2013). Environmental temperature ranged from 20.2 to 23.7◦C, humidity from 27 to 61%, and barometric pressure from 741 to 758 mmHg.

Heart Rate For trials 1 and 2, HR was measured beat-by-beat using a

team system (Suunto team POD, Suunto Oy, Vantaa, Finland). For trial 3, HR was measured beat-by-beat using an individual HR transmitter coupled to a receiver (Polar Vantage NV, Polar Electro Oy, Kempele, Finland). HRpeak was defined for all trials as the highest HR averaged over a 5 s rolling window.

#### Metabolic

In trials 1 and 3, lactate concentration in haemolysed whole blood ([L− a ]B) was assessed at rest and immediately postexercise using an automated analyser [Biosen C-line Sport, EKF Diagnostics, Barleben, Germany (Trial 1) or YSI 1500 SPORT, YSI Incorporated, Yellow Springs, OH, USA (Trial 2)]. In trial 3, oxygen uptake (Vo˙ 2) was assessed using an online system (MetaLyzer 3B, Cortex Biophysik GmbH, Leipzig, Germany). Vo˙ 2peak was defined as the highest Vo˙ 2 over a 30 s rolling window.

## Statistics

Between-trial differences in physiological outcomes were assessed using either a one-way repeated-measures ANOVA (HR) or paired sample t-test ([L− a ]B). Relationships between peak physiological indices from field- and laboratory-based testing were assessed using Pearson's product moment correlation. Statistical analyses were carried out using STATA v12.0, with significance set at p < 0.05.

# RESULTS

Individual athlete data for all trials are reported in **Table 1**. HRpeak was different between trials (p = 0.0035) and post-hoc testing revealed HRpeak was higher in trial 1 and trial 2 vs. trial 3 (p = 0.008 and p = 0.048, respectively). There was no difference in HRpeak between trial 1 and trial 2 (p = 0.29), and the values during both field-based exercise tests were strongly correlated (r = 0.88, p = 0.002; **Figure 1B**). There were no significant correlations between HRpeak achieved during the field-based tests and HRpeak achieved in the laboratory (r = 0.56–0.61, p > 0.08). During field-based testing, HR increased rapidly at the onset of exercise in all athletes and remained elevated throughout (**Figure 1C**). Blood lactate concentration was higher during trial 1 vs. trial 3 (p = 0.010; **Figure 1D**).

# PERSPECTIVE

For the first time we report that peak heart rate and blood lactate concentration during maximal field-based exercise testing exceed values attained during maximal incremental laboratory-based wheelchair exercise on a treadmill. This suggests that incremental exercise testing in the laboratory, at least using the protocol described herein, does not elicit true peak cardiometabolic responses in highly-trained wheelchair rugby athletes with cervical SCI.

The HR values elicited during our laboratory-based treadmill test typify those reported in previous studies that have used wheelchair ergometry or treadmill exercise to investigate peak exercise responses in tetraplegic athletes (Coutts et al., 1983; Wicks et al., 1983; Lasko-McCarthey and Davis, 1991; Schmid et al., 1998; Paulson et al., 2013; Leicht et al., 2014; West et al., 2014a). An interesting observation from the two field-based trials compared to the laboratory trial was the push technique utilized. In the field-based trial, the athletes favored three small pushes followed by a short break for deep inhalation. During the push-phase many athletes also tended to "lean" into the abdominal strapping used to secure them into their sports chair. Anecdotally, athletes report that this push technique allows them to produce more force (power) with each push stroke. Leaning into the chest strapping likely compresses the abdomen and impairs diaphragmatic descent. In turn, this would be expected to reduce the force generating capacity of the diaphragm and may explain why athletes had to pause every three strokes for

Trial 1: 4 min field-based maximal exercise test; trial 2: 40 min field-based maximal exercise test; trial 3: maximal laboratory-based incremental wheelchair propulsion test on a treadmill; IWRF, International Wheelchair Rugby Federation; HR, heart rate; [L− a ]B, blood lactate concentration; Vo˙ 2, oxygen uptake. \*Significantly different from trial 3 (p < 0.05).

deep inhalation. On a treadmill, this technique is impossible to replicate as the wheelchair would roll to the back of the treadmill if pushing were to cease, thereby terminating the test. Thus, different push patterns may have been responsible for the lower cardiometabolic responses during treadmill exercise. To our knowledge, no study has directly compared maximal push mechanics between laboratory- and field-based testing in tetraplegic athletes. In able-bodied individuals, recent research suggests that current treadmill wheelchair propulsion protocols are unable to accurately reproduce the forces applied during fieldbased (i.e., over ground) propulsion (Mason et al., 2014). It is not yet clear whether these findings translate to highly-trained athletes with cervical SCI. An interesting observation was that the heart rate in three athletes (#1, 5, and 6) was similar between field- and laboratory-based testing. It is unclear why this was the case for these three athletes only. One explanation could be that these three athletes utilize a push technique that can easily be replicated in both the laboratory and field conditions. The idea of "transferability" of different propulsion techniques between laboratory and field settings has to our knowledge never been investigated in elite tetraplegic athletes but may provide important insight as to why some athletes can achieve similar maximal exercise responses in both the laboratory and field settings whilst others cannot.

Lower laboratory-based HR responses may also be a consequence of the inferior metabolic demand of incremental laboratory exercise compared to high-intensity constant load exercise. Increased acidosis associated with a higher blood lactate concentration in the field would be expected to drive greater peripheral and central chemoreceptor activation and augment central sympathetic outflow (Somers et al., 1989). In cervical SCI athletes with autonomic incomplete injuries, central sympathetic stimulation would elicit a direct and indirect (catecholaminergic) inotropic response. In autonomic complete athletes, it is possible that the sub-lesional sympathetic circuitry can still be activated from chemoreflexes via the pulmonary stretch receptors. Unfortunately, no studies have examined the interactions between chemoreceptor activation and vasomotor outflow after SCI. Moreover, while circulating catecholamines increase marginally during wheelchair ergometry in untrained cervical SCI (Schmid et al., 1998), no study has investigated the catecholaminergic response to field-based exercise. In our opinion, such studies are critical to advance our understanding of the physiological responses to exercise in athletes with cervical SCI.

The field-based measures of physiological performance reported herein are relatively crude, but are typical of those collected by researchers and/or sports physiologists during sports-specific field-based testing. We are yet to conduct fieldbased assessments of peak oxygen uptake using a portable metabolic cart. Such measures are the next step to confirm that peak cardiometabolic responses during laboratory-based exercise testing are indeed inferior to those obtained in response to fieldbased exercise testing. Nevertheless, we measured HR values that were considerably higher during both short- and longduration field-based exercise compared to laboratory testing. Thus, future research should investigate why field-based exercise testing provides superior cardiometabolic responses (at least for most athletes) and seek to optimize maximal treadmill testing protocols. Until such studies are carried out we suggest that sports physiologists working in applied settings continue to use both laboratory and field-based testing and that the choice of test should be dictated by the question at hand as well as the availability of resources. Field-based maximal exercise testing provides superior external validity, the ability to accommodate large groups, and the free choice of push mechanics. Conversely, a laboratory-based exercise test allows for a more detailed physiological assessment under carefully controlled conditions with respect to protocol, temperature, and humidity.

# CONSIDERATIONS

We chose to use laboratory-based wheelchair propulsion to investigate peak responses because it is the most externally valid laboratory modality and because peak responses are slightly higher during wheelchair propulsion than during other laboratory modalities such as arm-crank exercise (Gass and Camp, 1984). Our decision to increment grade only was based on previous research that reported no significant differences in peak responses between treadmill protocols which increment speed, gradient, or a combination of both (Hartung et al., 1993). Finally, our participants were highly motivated wheelchair rugby athletes who were well versed in maximal incremental exercise testing. We are confident therefore that the laboratory testing environment was conducive to eliciting peak responses

REFERENCES

in the laboratory. That we measured similar HRpeak values during both field tests suggests that higher values in the field are indeed a real phenomenon and not an anomaly. Moreover, the mean values reported in the present study are almost identical to our previous field-based assessments of Paralympic hand-cyclists with cervical SCI (West et al., 2015). Finally, environmental conditions were similar between Trial 1 and 3 (not noted for Trial 2), suggesting differences in environmental conditions do not explain between-test differences in physiological responses. Thus, we are confident that the data presented herein represent true differences in physiological responses between laboratory- and field-based exercise testing.

#### CONCLUDING REMARKS

The present data imply that peak physiological indices measured in response to maximal incremental exercise testing in the laboratory using current protocols may not represent true maximal responses for athletes with tetraplegia. We suggest that future studies should investigate why fieldbased exercise testing provides superior cardiometabolic responses and seek to optimize maximal treadmill testing protocols to probe true peak responses in elite athletes with cervical SCI.

#### ACKNOWLEDGMENTS

The authors thank the Great Britain Wheelchair Rugby squad for participating in our research.

athletes with cervical spinal cord injury. J. Appl. Physiol. 117, 36–45. doi: 10.1152/japplphysiol.00218.2014

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2016 West, Leicht, Goosey-Tolfrey and Romer. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# Effect of Three Different Grip Angles on Physiological Parameters During Laboratory Handcycling Test in Able-Bodied Participants

Thomas Abel 1 \*, Brendan Burkett 2 , Barbara Thees 1 , Stefan Schneider 1 , Christopher D. Askew2 and Heiko K. Strüder 1

1 Institute of Movement and Neurosciences, German Sport University Cologne, Cologne, Germany, 2 Faculty of Science, Health, Education and Engineering, School of Health and Sport Sciences, University of the Sunshine Coast, Maroochydore, QLD, Australia

#### Edited by:

Pierre-Marie Leprêtre, Université de Picardie Jules Verne, France

#### Reviewed by:

Philip Santos Requejo, Rancho Los Amigos National Rehabilitation Center, USA Arnaud Faupin, Université de Toulon, France

> \*Correspondence: Thomas Abel<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Exercise Physiology, a section of the journal Frontiers in Physiology

Received: 13 August 2015 Accepted: 02 November 2015 Published: 23 November 2015

#### Citation:

Abel T, Burkett B, Thees B, Schneider S, Askew CD and Strüder HK (2015) Effect of Three Different Grip Angles on Physiological Parameters During Laboratory Handcycling Test in Able-Bodied Participants. Front. Physiol. 6:331. doi: 10.3389/fphys.2015.00331 Introduction: Handcycling is a relatively new wheelchair sport that has gained increased popularity for people with lower limb disabilities. The aim of this study was to examine the effect of three different grip positions on physical parameters during handcycling in a laboratory setting.

Methods: Twenty one able-bodied participants performed three maximum incremental handcycling tests until exhaustion, each with a different grip angle. The angle between the grip and the crank was randomly set at 90◦ (horizontal), 0◦ (vertical), or 10◦ (diagonal). The initial load was 20 W and increased by 20 W each 5 min. In addition, participants performed a 20 s maximum effort.

Results: The relative peak functional performance (W/kg), peak heart rate (bpm), associated lactate concentrations (mmol/l) and peak oxygen uptake per kilogram body weight (ml.min−1 .kg−1 ) for the different grip positions during the stage test were: (a) Horizontal: 1.43 ± 0.21 W/kg, 170.14 ± 12.81 bpm, 9.54 ± 1.93 mmol/l, 30.86 ± 4.57 ml/kg; (b) Vertical: 1.38 ± 0.20 W/kg, 171.81 ± 13.87 bpm, 9.91 ± 2.29 mmol/l, 29.75 ± 5.13 ml/kg; (c) Diagonal: 1.40 ± 0.22 W/kg, 169.19 ± 13.31 bpm, 9.34 ± 2.36 mmol/l, 29.39 ± 4.70 ml/kg. Statistically significant (p < 0.05) differences could only be found for lactate concentration between the vertical grip position and the other grips during submaximal handcycling.

Conclusion: The orientation of three different grip angles made no difference to the peak load achieved during an incremental handcycling test and a 20 s maximum effort. At submaximal load, higher lactate concentrations were found when the vertical grip position was used, suggesting that this position may be less efficient than the alternative diagonal or horizontal grip positions.

Keywords: adapted physical activity, biomechanics, spinal cord injury

# INTRODUCTION

Handcycling has opened a new world of mobilization for people who are restricted to a wheelchair, from both a health perspective (Abel et al., 2003a; Arnet et al., 2016) and for sports performance (Abel et al., 2006; Goosey-Tolfrey et al., 2006; de Groot et al., 2014). During the last 5 years, race performance has increased significantly with the adoption of elite athlete training approaches and technical developments concerning the handcycle itself. In comparison to wheelchair propulsion, handcycling has a higher mechanical efficiency (Abel et al., 2003a; Dallmeijer et al., 2004; Simmelink et al., 2015; Arnet et al., 2016), which gives the person restricted to a wheelchair the benefit of increased mobility. It has been postulated that regular engagement with handcycling will likely lead to fewer painful and debilitating overuse injuries (van der Woude et al., 2006; Arnet et al., 2014). Energy expenditure in handcycling is sufficient to offer protection against the development of secondary conditions such as cardiovascular disease (Abel et al., 2003a; van der Woude et al., 2013). As a relatively new device there have been a range of areas investigated to improve handcycle performance, such as the influence of back rest position, gear ratios (Faupin et al., 2008; Arnet et al., 2014). Whilst the efficiency of the athlete and handcycle as a complete system has been assessed, the influence of some key components within this system have not yet been quantified, such as the type or orientation of the hand grip.

As a mechanical device, the transmission of force from the athlete to the cycle plays a major role in handcycling performance. To better understand this interface between the athlete and the cycle, the influence of crank length (Goosey-Tolfrey et al., 2008; Krämer et al., 2009) and crank patterns (Verellen et al., 2004, 2008) on the transmission of forces has been investigated. In fine tuning this connection further, the configuration of cranking, either synchronous or asynchronous, has also been investigated (Hopman et al., 1995; Mossberg et al., 1999; Abel et al., 2003b; Dallmeijer et al., 2004; Goosey-Tolfrey and Sindall, 2007; van der Woude et al., 2008). To date the research on crank configurations has failed to address the critical question of hand-crank grip position. From a purely anatomical perspective, the musculoskeletal structure of the human forearm is a significant determinant of the ergonomics of the wrist, with the maximum generation of force found when the wrist is orientated near maximum flexion (Morse et al., 2006; Khan et al., 2009). Due to their disability, the users of a handcycle often have some degree of movement limitation in their forearm, therefore the optimisation of grip position for these athletes is of great importance (Bressel et al., 2001). In practice, disabled athletes commonly self-experiment with different grip angels and different grip forms. To investigate the optimal grip-crank interface, the aim of this study was to examine the effect of three different grip angles on the physiological responses to incremental and maximal handcycling in a laboratory setting. The hypothesis herby is that altering the grip orientation, and therefore altering the muscle length and specific load applied to the forearm and upper muscles, will result in changes change in power generated as well as changes in physiological reactions at submaximal and maximal load.

# METHODS

# Participants

Twenty-one participants (15 male and six female; age 27 ± 5 years, height 178.0 ± 11.9 cm, weight 74.7 ± 13.3 kg) performed three stage tests until exhaustion with different grip angles. The participants were able-bodied and with a good training status of the upper extremity (active athletes in swimming and triathlon).

This study was carried out in accordance with the recommendations of guidelines of the International Committee of Medical Journal Editors. All subjects gave written informed consent in accordance with the Declaration of Helsinki. All investigations were approved by the German Sports University ethical advisory committee.

# Experimental Overview

For all tests, participants sat in an arm-power race handcycle (Sopur Shark, Sunrisemedical Germany) connected to an ergometer (Cyclus II, Richter; Germany). The crank length was 175 mm, backrest angle approximately 45◦ adapted to the participants to avoid full elbow extension during crank revolutions. Crank housing position was set on a horizontal line to shoulder angle, crank configuration synchronous. The Cyclus II ergometer has been validated as an accurate measure of handcycling work load (Reiser et al., 2000). The angle between the grip and the crank was set in one of three configurations (see **Figure 1**), (a) 90◦ (horizontal = H), (b) 0◦ (vertical = V) and (c) 10◦with respect to the vertical (i.e., diagonal, common way of cranking = D). Participants conducted an incremental test and a 20-s peak force test. The 20-s peak test was carried out after the incremental test und separated by 2 h. Tests were repeated three times using each of the grip configurations, in a random order, and each testing session was separated by a 3-day recovery period.

# Incremental Test Protocol

After a standardized warm up period, the participants commenced hand cycling using one of the defined grip positions. Cycling cadence was freely chosen above 50 rpm. The initial load during test was 20 W and increased by 20 W every 5 min until the load where the 50 rpm cadence was not able to be maintained.

Expired air was collected continuously (ZAN 600, ZAN, Germany) during exercise for the assessment of oxygen consumption. Immediately before every test session, gas analyzers were calibrated with known reference gas mixtures (room air and a standard certified commercial gas preparation). The expiratory airflow volume was calibrated using a 1.0-l syringe. Blood samples to determine lactate concentrations were taken from the earlobe during the last 30 s of each stage (Biosen C, Eppendorf, Germany). Heart rate was monitored continuously (Polar X-Trainer, Polar, Finland).

## Data Analysis

The descriptive mean and standard deviations for each of the measures of work, heart rate, blood lactate, and oxygen consumption were calculated using STATISTICA for Windows Version 7.1 F (StatSoft Inc, Tulsa, USA). An analysis of variance

TABLE 1 | Physiological values at peak load during the stage test.

with repeated measurements for submaximal and peak values was used to determine the presence of TIME and GRIP effects for heart rate, lactate and VO2peak. Post-hoc (least significant difference Test LSD) analysis was performed where there were significant main effects and interactions to determine the precise location of differences or changes. A P-value less than 0.05 was considered significant.

#### RESULTS

The peak functional performance (W/kg), peak heart rate (bpm), the associated lactate concentrations (mmol/l), and peak oxygen uptake per kilogram body weight (ml/kg) for the three different grip positions during handcyling are shown in **Table 1**.

As shown in **Figure 2**, there were no significant differences for peak oxygen uptake between the three grip positions during the incremental test. There were also no differences between the three grip positions for the other peak variables during handcycling, including functional performance, heart rate and blood lactate. **Figure 3** shows the lactate concentrations at defined submaximal work loads of 20, 60, and 100 W during the incremental test watts. There was a statistically significant difference between the vertical grip position and the other grips at 60 and 100 W.

Peak and average data for each of the variables during the 20 s all out test are shown in **Table 2**. No significant differences were found between the three gips positions.

#### DISCUSSION

The aim of this study was to examine the effect of three different grip angles on functional performance and associated physiological variables during handcycling. To the authors' knowledge, this aspect of handcycling has not been previously investigated.

While absolute an relative oxygen uptake tended to be lower at submaximal and peak workloads when the diagonal grip orientation was used, this was not statistically significant. Nonetheless, small reductions in oxygen uptake during laboratory tests may translate into important and significant improvements in economy during longer endurance activities such as a handcycling road race (Fischer et al., 2015). This time dependant relationship between work load and oxygen uptake has been identified in other studies (Verellen et al., 2004).

An unexpected finding was the higher blood lactate concentration during submaximal (60 and 100 W) handcycling when the vertical grip was used compared with both the diagonal and horizontal grips. As it is unlikely that lactate clearance would be different between the three test conditions (Heck et al., 1985; Mader, 2003), this elevation in lactate with the vertical grip indicates that there is likely to be a greater reliance on anaerobic metabolism by the working muscles. As these changes are unique to the vertical grip position, a plausible hypothesis could be that the vertical position requires increased static work, throughout the entire pedal stroke, to fix the hand at the handlebar. As sweat production, and the associated grip instability, increases with exercise intensity and time, this is likely to lead to further increases in static work and a greater reliance on local anaerobic metabolism. It is likely that this explains why many athletes avoid

TABLE 2 | Peak and mean work load during the 20 s test.

using the vertical grip in practice, and instead adopt a grip with some degree of horizontal orientation.

In the present study a full 90◦ grip range was explored to ascertain the most appropriate orientation of the handcrank grip. This complete range of movement was considered necessary, as previous cycling studies on crank length for example only considered small increments of change (Martin and Spirduso, 2001). Despite this maximum change in the range of motion of the grip orientation, there were no significant differences in force between the vertical, diagonal, and horizontal grip positions. The hypothesis that altering the grip orientation, and therefore altering the muscle length and specific load applied to the forearm and upper muscles, would result in a change in power generated as well as in efficiency related values was not supported. Based on the similar oxygen uptake and heart rate measures during each of the tests, the

#### REFERENCES

Abel, T., Kröner, M., Rojas Vega, S., Peters, C., Klose, C., and Platen, P. (2003a). Energy expenditure in wheelchair racing and handbiking - a basis for prevention of cardiovascular diseases in those with disabilities. Eur. J. economy of the three different grip orientations showed no difference.

Training with the optimal hand-crank orientation is essential for efficiency of movement, performance and the prevention of overuse risks (Webborn and Van de Vliet, 2012; Arnet et al., 2014). As the economy of movement when handcycling with the diagonal grip was only slightly, and non-significantly, higher than the other grip orientations for the able-bodied population, it would also seem important to consider comfort when setting up the handcycle, particularly for individuals with a loss of lower limb function. Depending on the unique and individual anatomy and movement restrictions of the athlete with a disability, the optimal handcycle setup and grip orientation may alter significantly form individual to individual.

#### Limitations of the Study

The testing was done in a stationary laboratory situation using the Cyclus II ergometer. The absent of a need or possibility to steer the handcycling as well as the able-bodied participant with limited handcycling experience might have influenced test results. This restricts the transferability of the test results onto athletes with spinal cord injuries or other disabilities. A real competitive test setup during a handcycling race, including participants with disabilities would have simulated this more significantly, but tests like that are more or less impossible to be conducted.

Nevertheless, as all grip angles were tested under the same laboratory situation, the results allow claiming relevance for handcycling athletes.

#### CONCLUSION

In the present study there were no differences between three different grip positions (horizontal, vertical, and diagonal) when handcycling at maximum intensity during an incremental test and during a sprint test. There was also no difference in the economy of hand cycling during submaximal loads when each of the three grips was used. The vertical grip was associated with higher lactate concentrations during submaximal handcycling, and may be indicative of reduced efficiency caused by the static (continuous) activation of the working muscles. Further, studies should be conducted to verify these findings during prolonged exercise bouts and in athletes with a spinal cord injury or similar disabilities.

#### ACKNOWLEDGMENTS

The study was supported by the Federal Institute of Sport Science VF 0407/04/41.2004.

Cardiovasc. Prev. Rehabil. 10, 371–376. doi: 10.1097/01.hjr.0000096542.305 33.59

Abel, T., Schneider, S., Platen, P., and Strüder, H. K. (2006). Performance diagnostics in handbiking during competition. Spinal Cord 44, 211–216. doi: 10.1038/sj.sc.3101845

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2015 Abel, Burkett, Thees, Schneider, Askew and Strüder. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# Comparison Between 30-15 Intermittent Fitness Test and Multistage Field Test on Physiological Responses in Wheelchair Basketball Players

#### Thierry Weissland1, 2 \*, Arnaud Faupin3, 4 , Benoit Borel 5 and Pierre-Marie Leprêtre1

1 Laboratoire de Recherche Adaptations Physiologiques à L'exercice et Réadaptation à L'effort, EA-3300, UFR-STAPS, Université de Picardie Jules Verne, Amiens, France, 2 Institut d'Ingénierie de la Santé, UFR de Médecine, Université de Picardie Jules Verne, Amiens, France, 3 Laboratoire Motricité Humaine Education Sport Santé, EA-6312, UFR-STAPS, Université de Toulon, La Garde, France, 4 Laboratoire Motricité Humaine Education Sport Santé, EA-6312, Université Nice Sophia Antipolis, Nice, France, 5 Laboratoire Handicap, Activité, Vieillissement, Autonomie, Environnement, EA-6310, Département STAPS, Université de Limoges, Limoges, France

#### Edited by:

Olivier Girard, University of Lausanne, Switzerland

#### Reviewed by:

Peter Hofmann, University of Graz, Austria Javier Yanci, University of the Basque Country, Spain

\*Correspondence: Thierry Weissland<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Exercise Physiology, a section of the journal Frontiers in Physiology

Received: 15 September 2015 Accepted: 24 November 2015 Published: 16 December 2015

#### Citation:

Weissland T, Faupin A, Borel B and Leprêtre P-M (2015) Comparison Between 30-15 Intermittent Fitness Test and Multistage Field Test on Physiological Responses in Wheelchair Basketball Players. Front. Physiol. 6:380. doi: 10.3389/fphys.2015.00380 The intermittent nature of wheelchair court sports suggests using a similar protocol to assess repeated shuttles and recovery abilities. This study aimed to compare performances, physiological responses and perceived rating exertion obtained from the continuous multistage field test (MFT) and the 30-15 intermittent field test (30-15IFT). Eighteen trained wheelchair basketball players (WBP) (WBP: 32.0 ± 5.7 y, IWBF classification: 2.9 ± 1.1 points) performed both incremental field tests in randomized order. Time to exhaustion, maximal rolling velocity (MRV), VO2peak and the peak values of minute ventilation (VEpeak), respiratory frequency (RF) and heart rate (HRpeak) were measured throughout both tests; peak and net blood lactate (1[Lact−] = peak–rest values) and perceived rating exertion (RPE) values at the end of each exercise. No significant difference in VO2peak, VEpeak, and RF was found between both tests. 30-15IFT was shorter (12.4 ± 2.4 vs. 14.9 ± 5.1 min, P < 0.05) but induced higher values of MRV and 1[Lact−] compared to MFT (14.2 ± 1.8 vs. 11.1 ± 1.9 km·h −1 and 8.3 ± 4.2 vs. 6.9 3.3 mmol L ± · −1 , P < 0.05). However, HRpeak and RPE values were higher during MFT than 30-15IFT(172.8 14.0 vs. 166.8 13.8 bpm and 15.3 ± ± ± 3.8 vs.13.8 ± 3.5, respectively, P < 0.05). The intermittent shuttles intercepted with rest period occurred during the 30-15IFT could explain a greater anaerobic solicitation. The higher HR and overall RPE values measured at the end of MFT could be explained by its longer duration and a continuous load stress compared to 30-15IFT. In conclusion, 30-15IFT has some advantages over MFT for assess in addition physical fitness and technical performance in WBP.

Keywords: wheelchair, basketball, field test, aerobic fitness, evaluation

# INTRODUCTION

Wheelchair basketball (WB) attracts many persons with different physical impairment and has great success at the Paralympic Games since 1960. WB has been described as intermittent aerobic-based sport scattered with short anaerobic bouts (Coutts, 1992; Bloxham et al., 2001). In their game analysis, Sporner et al. (2009) reported that the wheelchair basketball players (WBP) on average traveled 2679 ± 1103 m cut off by 239.8 ± 60.6 stops and starts during a match. Wheeling tasks including sprint, endurance, and slalom were strongly correlated with aerobic fitness in WBP (Hutzler, 1993; Vanlandewijck et al., 1999). WBP presented larger cardiac dimensions, greater power output and peak oxygen uptake (VO2peak) values compared to untrained counterparts (Huonker et al., 1998; Schmid et al., 1998). Thus, maximal oxygen uptake was correlated to functional capacity and competition level in WBP (Schmid et al., 1998; De Lira et al., 2010).

Cardiorespiratory adaptation to exercise provided valuable information on training status. VO2peak is generally assessed in laboratory condition during graded exercise performed on a wheelchair rolling on a motor driven treadmill and on an arm cycle ergometer. However, low correlations are obtained between peak cardiorespiratory values measured while pushing on the wheelchair and those measured with arm cranking on ergometer or in selected wheeling task (Hutzler, 1993; Rotstein et al., 1994). Standardized laboratory protocol tests can also provide higher VO2peak reached at the end of test compared to field tests (Cunningham et al., 2000; Goosey-Tolfrey and Tolfrey, 2008). However, laboratory conditions did not take into account the natural environment (floor surface, specific wheelchair equipment) and not relate specific skills at the environment and ability to maneuver the wheelchair (Bernardi et al., 2010; Molik et al., 2010; De Groot et al., 2012; Goosey-Tolfrey and Leicht, 2013). Several authors adapted continuous (Vinet et al., 1996; Vanderthommen et al., 2002; Bernardi et al., 2010) and shuttle (Vanlandewijck et al., 1999; Cunningham et al., 2000; Goosey-Tolfrey and Tolfrey, 2008) tests for able-bodied players to assess aerobic fitness and predict the VO2peak of disabled players. To assess agility, sprint recovery and endurance characteristics of WBP, Yanci et al. (2015) and Gil et al. (2015) also proposed a modified Yo-Yo intermittent recovery test (10-m instead of 20-m shuttle run). Yanci et al. (2015) showed a good test— retest reliability (ICC = 0.74–0.94; CV: ranged from 2.6 to 7.2%).

Buchheit (2008) developed for able-bodied athletes the 30- 15 Intermittent Field Test (30-15IFT), which aims to evaluate the maximal aerobic velocity in court sport players and acute responses to high-intensity intermittent shuttle-runs. The main interests of this test is the final speed reached at the end of the test which is well suited for training prescription and the rest time is longer than the Yo-Yo intermittent recovery test and more representative of defensive phase of WP (Buchheit and Rabbani, 2014). Nevertheless, wheelchair sports are distinct from those able-bodied due to functional impairment of the disabled and the displacement imposed by wheelchair (Goosey-Tolfrey and Leicht, 2013).

Previously, an incremental multistage field test (MFT) specific for disabled body wheelchair subjects was validated (Vanderthommen et al., 2002). It was observed that a slightly MFT adaptation—as alternating right and left turns vs. single direction—increase VO2peak and peak minute ventilation (VEpeak) responses without any significant differences in perceived exertion and maximal rolling velocity (MRV) reached at the end of the test (Weissland et al., 2015). These adjustments have no correspondence with the intermittent nature and the metabolic and cardio-respiratory responses induced by pivots, sprints and dribbles requested in WBP. Moreover, it has been observed, in able-bodied team sport players, that higher peak velocity were reached with a shorter time to exhaustion in intermittent shuttle vs. continuous running tests, with no significant difference in peak values of heart rate (HRpeak) and blood lactate (Carminatti et al., 2013).

Hence, the aim of the study was (i) to assess the aerobic fitness derived from an able-bodied intermittent field test in WBP (Buchheit, 2008) and (ii) to compare with a continuous and validated wheelchair field test. This study aimed to examine the end-test rolling velocity, the physiological responses and perceived exertion obtained from the continuous MFT and with the 30-15 intermittent field test (30-15IFT).

# METHODS

### Subjects

Eighteen national WBP were recruited and all were engaged in national WB competitions every week, with several training sessions per week. Skinfolds thickness at four sites (triceps, subscapular, suprailiac, and abdominal) was measured using a Harpenden caliper. A summary of their characteristics, pathology and international classification (International Wheelchair Basketball Federation Web site, 2009) is presented in **Table 1**. For both tests, all players always used their own wheelchair. Before each test, the tire pressure was checked (Sawatzky et al., 2005). All procedures were conducted in accordance with approval of the "Fédération Française Handisport" medical committee, and in accordance with the Helsinki Declaration. All participants are fully informed of any risk giving and provided written informed consent.

#### Experimental Design

Testing for this study was conducted during the competitive period, in the middle of the season. Both tests replaced technical and physical training sessions during a week between competitive matches. Training load was reduced on the day preceding each test, which was performed between 9:00 a.m. and 4:00 p.m. Each WBP performed both tests within 48 h in a randomized order, in the same indoor hall: (i) the MFT which is an incremental continuous test (Vanderthommen et al., 2002) and (ii) the 30- 15 intermittent fitness test (30-15IFT) (Buchheit, 2008). Briefly, the MFT included wheeling around an octagon (15 × 15 m) at an initial speed of 6 km·h −1 during 1 min. Then, the speed increased by 0.37 km·h −1 every minute until exhaustion (Vanderthommen et al., 2002). The 30-15IFT consisted of 40-m shuttle runs during 30-s with 15-s of passive recovery. The initial velocity was set at 6 km·h −1 (instead of 8 km·h −1 in the original protocol) for the first 30-s trial and was increased by 0.5 km·h −1 every 45-s

TABLE 1 | Individual Wheelchair basketball players' characteristics (gender, age, disability, sum of four skinfolds) according to International Wheelchair Basketball Federation classification (IWBF).

6SK represents the sum of four skinfolds (biceps, triceps, subscapular, supra-iliac).

(Buchheit, 2008). During the 15-s recovery period, the subjects rolled in the forward direction to join the closest line (at the middle or at one end of the area, depending on where they stopped) from where they started the next stage. No indication for the propulsion strategy was given for the two tests and WBP freely used their push rate and modality (synchronous and/or asynchronous).

All participants were instructed to complete as many stages as possible. The test ended when the participant could no longer be located within the turning zone (MFT) or consecutively to reach a 2-m zone around each line (30-15IFT) at beep signal despite verbal encouragement. The time to exhaustion (TTE) was the longer time maintaining to the speed imposed on the last stage during each respective test. MRV was the velocity at the end of test reached at the TTE.

All subjects were advised to keep the same meals between both tests and to refrain from smoking and caffeinated drinks during the 2 h prior to testing.

## Physiological and Perceived Responses Measurements

The resting oxygen uptake (VO2), carbon dioxide production (VCO2), respiratory frequency (RF), and minute ventilation (VE) were measured breath-by-breath at rest and throughout both tests using Cosmed K4b2 or Metamax 3B portable spirometric systems. To reduce the duration of the test time and the turnover subjects, two portable measurement systems were used. A previous study showed a satisfactory comparison between the two measuring devices with able-bodied cyclists (Leprêtre et al., 2012). Participants always used the same analyzer for both tests to repeat the mistake device. The turbines flow meters (with a 3-L syringe) and analysers were calibrated before each test, according to the constructor instruction manuals using a twopoint calibration (calibration gas O2 = 16% and CO2 = 5% against room air). Then we used the software of each device to automatically eliminate ectopic values and average the data every 5 s. Heart rate (HR) was continuously recorded beat-tobeat (Polar RS800, Polar Electro, Kempele, Finland) and averaged every 5 s.

Small capillary blood samples (0.5µL) were collected from finger to assess basal lactate concentration. A sample of lactate at rest was taken upon arrival of the player and before warmup, immediately after the test and 3 min after during the passive recovery period. Net blood lactate values (1[Lact−]) were calculated by the difference between the peak [Lact−] values and rest values. All blood samples were analyzed using a portable lactate analyzer (Lactate Pro, Arkray, Japan) calibrated before each test using a standard strip of provided by the manufacturer (Pyne et al., 2000).

Immediately after the end of both tests, participants individually rated their overall perceived exertion (RPE) using the Borg's 6–20 scale (Borg, 1990).

#### Statistical Analysis

Descriptive data are presented as mean and standard deviation (mean ± SD). Normality and homogeneity of the distribution were verified via Shapiro Wilks and Levene tests, respectively. Student's t-test was used to compare the resting and peak values measured during MFT and 30-15IFT. The determination of the Pearson correlation coefficients (R) were used to examine the relationship between TTE, MRV, VO2peak, and condition test. Absolute effect size (ES) and 95% confidence intervals of the differences (95% CI) were computed. An ES of 0.2 refers to a small effect, 0.5 a moderate effect, and 0.8 a large effect according to Cohen (Cohen, 1992). Agreements were sought by the Bland and Altman' method (Bland and Altman, 1986) between the peak values of VO2 and VE between the both tests. In all statistical analyses, the (alpha) level of significance was set at P < 0.05.

#### RESULTS

Peak values of cardiorespiratory responses and performance measured during MFT and 30-15IFT are shown in **Table 2**. Higher MRV values (14.2 ± 1.8 vs. 11.1 ± 1.9 km·h −1 , P < 0.05, ES = 0.6) and shorter TTE (12.4 ± 2.4 vs. 14.9 ± 5.1 min, P < 0.05, ES = 0.3) were observed during 30-15IFT compared to MFT. HRpeakand RPE values were significantly lower during 30-15IFT compared to MFT (166.8 ± 13.8 vs. 172.8 ± 14.0 bpm, ES = 0.4, and 13.8 ± 3.5 vs. 15.3 ± 3.8, ES = 0.5, P < 0.05, respectively). 30-15IFT induced a higher 1[Lact−] values compared to MFT (8.3 ± 4.2 vs. 6.9 ± 3.3 mmol·L −1 , P < 0.05, ES = 0.4) without any significant difference between rest (P = 0.88) and peak [Lact−] values (9.8 ± 4.4 mmol·L −1 vs. 8.5 ± 3.1, P = 0.2, ES = 0.3). No significant difference was found for VO2peak, VEpeak, and RF peak values between both tests.

A significant relationship for MRV (r = 0.57, P < 0.05) TTE (r = 0.64, P < 0.05), and VO2peak (r = 0.84, P < 0.01) was found between MFT and 30-15IFT(**Figure 1**). The Bland–Altman plots showed that, for VO2peak and VEpeak measurements, the bias ± random error was acceptable with an acceptable agreement between both tests (−0.27 ± 6.81 ml.min.kg−1 ; **Figure 2A** and 2.6 ± 34.8 L.min−1 ; **Figure 2B**, respectively). Differences between MFT and 30-15IFT HRpeak and 1[Lact−] per WBP were reported in **Figure 3**. Individual responses have reflected significant changes measured in HR (**Figure 4**) and 1[Lact−] for 30-15IFT.

#### DISCUSSION

The aim of this study was to compare a modified able-bodied field intermittent test with a validated standardized wheelchair-users field test. The observed performances at 30-15IFT were better with higher MRV associated with a shorter time to exhaustion (P < 0.05). However, no significant difference for peak oxygen uptake and ventilation values was noted between both tests (**Table 2**).

MFT is a validated field test to estimate VO2peak for disabled body wheelchair subjects in indoor conditions (Vanderthommen et al., 2002). No significant difference was found for VO2peak between MFT and 30-15IFT and a significant relationship for VO2peak were found between the both tests (r = 0.84, P < 0.01) (**Figure 1**). We used Bland-Altman plots to graphically display the variability of VO2peak and VEpeak variables (**Figure 2**). In each case, the systematic bias is close to zero and the 95% limits of agreements are acceptable.

FIGURE 1 | Correlation between VO2peak reached during MFT and 30-15IFT tests (r = 0.54, r 2 = 0.71, P < 0.01).

Thus, we can conclude that the 30-15IFT is comparable to VO2peak and VEpeak encountered during the end of the test. Nevertheless, it would be necessary in the future to investigate the reliability and validity of the 30-15IFT with a standardized test on a wheelchair ergometer in the laboratory. However, the only valid option to confirm whether a "true" VO2max has been reached during both tests is currently in a verification phase (VER) (Leicht et al., 2013), absent in our protocol.

TTE, indicates Time To Exhaustion; MRV, Maximal Rolling Velocity; RF, peak respiratory frequency; VEpeak , peak values of ventilation; VO2peak, peak oxygen uptake; HRpeak , peak heart rate; peak [La−], peak blood lactate value; 1[La−], the difference between rest and maximal blood lactate values; RPE, the rating of perceived exertion. \*Significantly different from MFT (P < 0.05); θ moderate effect size; γ small effect size (Cohen, 1992).

TTE to reach VO2peak is shorter during 30-15IFT than MFT (12.4 ± 2.4 vs. 14.9 ± 5.1 min, P < 0.05, ES = 0.3) and a significant correlation between both TTE tests was found (r = 0.64, P < 0.05). To reach VO2max, Buchfuhrer et al. (1983) recommended a time span of 10 ± 2 min for an incremental ramp protocol. This widely cited recommendation is applied for incremental protocols with able-bodied participants but also for upper body exercises and disabled subjects. With 16 untrained able-bodied men, Smith et al. (2006) observed, during an incremental arm crank ergometry, the effects of two ramp rates (12W·min−1 vs. 6W·min−1 ) on the attainment of peak physiological responses and power output (Smith et al., 2006). In this study, TTE was shorter for the 12W·min−1 protocol (within the range of 8–12 min) whereas, for the 6W·min−1 protocol, TTE extends to 15 ± 4 min. However, no significant difference was found for VO2, VE, and HRpeak between both protocols. In wheelchair athletes, Vinet et al. (1997) adjusted the velocity increment from a progressive treadmill test to be within the limits defined by Buchfuhrer et al. (8:50 ± 1:24 min). The Modified Yo-Yo intermittent recovery test (10 m shuttle run) provides higher TTE (16.96 ± 1.14 min), as reported by Yanci et al. (2015) in WBP. Considering the recommendations of time span (between 8 and 12 min) and given the absence of differences in the peak physiological responses, IFT30−15 would be more appropriate than MFT for the trained participants, due to the shorter TTE required for reaching VO2peak.

The difference in HRpeak measured at the end during both tests (166.8 ± 13.8 vs. 172.8 ± 14.0 bpm for 30-15IFT and MFT, respectively, ES = 0.4, P < 0.05) can be explained by the intermittent nature of the 30-15IFT, which is based on

the use of 15-s passive rest periods between each stage. HR responses represented as an example in **Figure 4** for the 12 WBP clearly show the difference in HR evolution between the two tests. 30-15IFT therefore allows a discontinuous load stress for WBP. 30-15IFT does not elicit maximal HR and the maximal capabilities of the cardiovascular system while some other criteria for the attainment of a maximal exercise (like VO2 plateau, RER > 1.1, lactate concentration accumulates > 8 mmol.L−1 ) were achieved. A peripheral limitation may explain the submaximal values for HRpeak. Vanlandewijck et al. (1999) has supported that shuttle test is not a direct measure of aerobic capacity but rather reflects ability and specific skills using the wheelchair. Indeed, Goosey-Tolfrey and Tolfrey (2008) showed that cardiorespiratory responses during a continuous shuttle multi-stage fitness test did not fully reflect those obtained during an exercise on arm crank ergometer. With WBP population, Yanci et al. (2015) reported greater HRpeak values (+4.7%) with a longest time (+36%) with Yo-Yo intermittent recovery test than the 30-15IFT. One other explanation can be the disruption of the autonomic control of the HR in three subjects with high spinal cord lesion, which would control the cardiovascular function during exercise and rest (West et al., 2014).

Peak RPE measured during MFT are consistent with the level of cardio-respiratory solicitations but RPE should be used cautiously for spinal cord injury athletes and differentiated for high and low lesion (Goosey-Tolfrey et al., 2010). Test duration and monotony of continuous displacement in MFT could increase the overall rate of perceived exertion during MFT in comparison with 30-15IFT (15.3 ± 3.8 vs. 13.8 ± 3.5 ES = 0.5, P < 0.05). Turning in the same direction during MFT could induce premature tiredness and muscle fatigue in the upper limb of the external curve. This could be in relation to the great push power output and high arm frequency and the centrifugal force exerted on the wheelchair in the curve. With novice wheelchair users, Paulson et al. (2013) showed self-regulation of intermittent exercises based on the overall or peripheral perceptions. Dissociating muscular and respiratory RPE in order to analyze match load is a feasible method of quantification in monitoring the training of WBP (Iturricastillo et al., 2015). In our study, overall RPE did not provide information of the muscular load perceived by the succession of starts and changes of direction in the 30-15IFT's protocol. An evaluation of peripheral RPE would certainly have given additional information between the two tests.

Higher MRV values were reached in a shorter time during 30-15IFT compared to MFT (14.2 ± 1.8 vs. 11.1 ± 1.9 km·h −1 , P < 0.05, ES = 0.6). 30-15IFT adaptation by initially starting at 6 km·h −1 allowed to extend the standard protocol of 3-min, in order to have the same initial velocity between MFT and 30- 15IFT. Despite this modification, 30-15IFT induces shorter TTE. It is explained by the difference in less than 15-s and in addition to 0.13 km·h −1 per stage in detriment to MFT between the both tests. Also for these reasons, MRV attained higher values at 30-15IFTthat MFT for similar VO2peak.

Higher 30-15IFT's MRV could explain the higher peak blood lactate values. Smith et al. (2006) measured higher peak [Lact−] for 12 W·min−1 ramp protocol and had argued that the higher workload increment than 6 W·min−1 was linked with higher lactactes concentration. In this study, the workload during the graded exercise has an impact on the muscular component. Thus, compared with continuous octagonal line rolling in MFT, 30-15IFT with direction changes and multiple acceleration phases could present a greater physiological load, as supported by relative blood lactate concentration and the extra energy expended. 1[Lact−] 30-15IFT values compared to MFT were higher (8.3 ± 4.2 vs. 6.9 ± 3.3 mmol·L −1 , P < 0.05, ES = 0.4). The significant increase of velocity per 0.5 km·h −1 at IFT after rest period, added to direction changes, deceleration and acceleration phase generate significant muscular efforts and greater anaerobic solicitation. However, Yanci et al. (2015) reported, for the modified Yo-Yo protocol, lower peak [Lact−] values than our data (7.21 ± 2.4 mmol·L −1 vs. 9.8 ± 4.4 mmol·L −1 ). Intermittent field tests correspond to the nature of the court sport in WB. Comparing Yo-Yo and 30-15IFT with young soccer players, Buchheit and Rabbani (2014) have noted a large correlation (r = 0.75) between both tests, with 30-15IFT being more related to maximal sprinting speed and Yo-Yo being more associated with aerobic endurance. Bloxham et al. (2001) showed with the Canadian team that 28% of the WB playtime was spent at high anaerobic intensities and estimated 20% above the ventilatory threshold. But, 48.3% of playtime concerns recovery and low-speed replacement periods. Considering these aspects, 30-15IFT could be closer to the WB conditions than the Yo-Yo intermittent test. Intermittent field testing would also have the advantage in determining the BLa threshold rather than ventilatory data collection (Leicht et al., 2014) with the sample blood lactate at each level.

Using able-bodied field tests to assess the physical condition of athletes with disabilities remains difficult and even imperfect (Goosey-Tolfrey and Leicht, 2013). First, pushing for inducing wheelchair rolling is not comparable to running. The amount of energy required for the inertia of the wheelchair are different, especially to start, to turn or to glide at half turn. Secondly, the initial rolling velocity is often inappropriate and the increment may be too important. In these conditions, shuttle protocols need a great technique or ability to maneuver the wheelchair and could limit the wheelchair novices and players with a low classification point (IWBF) that have more significant disabilities than the others. Shuttle tests could be more disadvantageous for athletes with greater disabilities than MFT in which the participants determine their preferred direction of rotation (Vanlandewijck et al., 1999). Functional asymmetry with a dominant side and contralateral side deficit in strength, imbalance had low impact for the physiological responses and MRV that are related between both tests (r = 0.57, P < 0.05). Heterogeneity of pathologies and residual functional capabilities represented in our study provide individual responses as shown in **Figure 3**.

Maneuvering a wheelchair during acceleration-deceleration phases, slide and half turns requires specific skills, considering individual muscular impairments and trunk imbalance. A moderate to high level of expertise of these techniques is essential for not stopping prematurely in 30-15IFT. It would be useful to compare our results during 30-15IFT with other untrained or novice wheelchair users in order to determine if 30-15IFT is also adaptable to various populations like MFT. Sprinting ability and

#### REFERENCES

wheelchair maneuverability are probably important predictors of performance in WBP (Vanlandewijck et al., 1999; Granados et al., 2015; Yanci et al., 2015). Thus, the 30-15IFT has the advantage to assess, in addition to physical fitness, the technical performance to maintain wheeling velocity with succession of alternating turns. MFT was originally developed to assess aerobic fitness of the wheelchair users without a GTX laboratory protocol. MFT is validated and the VO2peak extrapolation equation from MFT-score is reliable, repeatable and similar to VO2peak measured (Vanderthommen et al., 2002; Weissland et al., 2015). However, MFT protocol is not representative of the WB nature while intermittent field tests are more similar but would need assessment to determine their level of reliability, validity and sensitivity.

As a take home message, the MFT test is more appropriate for the determination of maximal physiological capacities of WBP and the associated MRV can be used for the individualization of pre-season training programs. However, with a shorter time to exhaustion, 30-15IFT is also really interesting and relevant for the evaluation of the WBP. This intermittent field test allows reaching VO2peak with a higher contribution of the anaerobic metabolism, while also assessing and taking into account the specific technical characteristics of WB. The important differences for peak HR, [Lact−] and MRV values between both tests emphasize the importance of an adequate and relevant test selection, according to the parameter of interest.

## CONCLUSION

The 30-15 Intermittent Fitness Test induced a higher MRV with a greater blood lactate value but lower heart rate and perceived exertion compared to the original continuous MFT. Moreover, time of exhaustion is shorter for 30-15IFT with similar peak oxygen uptake reached at the end of both test. Intermittent field test has some advantages over MFT for jointly assessing physical fitness and technical ability of WBP. It would be necessary in the future to investigate the reliability and validity from a standardized test on wheelchair ergometer in the laboratory.

### ACKNOWLEDGMENTS

The authors also thank the athletes and their coaches for their participation to this study. We warmly thank ≪ Fédération Française Handisport ≫ collaborating for this study. The authors wish to thank Clare Doyle for his participation.

wheelchair basketball players. Sports Med. Train. Rehabil. 10, 183–198. doi: 10.1080/1057831021039

between athletes functional classification level and disability type. Fizyo. Rehabil. 21, 11–19.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2015 Weissland, Faupin, Borel and Leprêtre. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# Performance changes and relationship between vertical jump measures and actual sprint performance in elite sprinters with visual impairment throughout a Parapan American games training season

#### Edited by:

Thomas Janssen, VU University Amsterdam, Netherlands

#### Reviewed by:

Naoto Fujii, University of Ottawa, Canada Alvaro N. Gurovich, Indiana State University, USA

#### \*Correspondence:

Irineu Loturco<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Exercise Physiology, a section of the journal Frontiers in Physiology

Received: 28 August 2015 Accepted: 26 October 2015 Published: 06 November 2015

#### Citation:

Loturco I, Winckler C, Kobal R, Cal Abad CC, Kitamura K, Veríssimo AW, Pereira LA and Nakamura FY (2015) Performance changes and relationship between vertical jump measures and actual sprint performance in elite sprinters with visual impairment throughout a Parapan American games training season. Front. Physiol. 6:323. doi: 10.3389/fphys.2015.00323 Irineu Loturco1 \*, Ciro Winckler 2 , Ronaldo Kobal 1 , Cesar C. Cal Abad1 , Katia Kitamura1 , Amaury W. Veríssimo2 , Lucas A. Pereira1 and Fábio Y. Nakamura1, 3

1 Nucleus of High Performance in Sport, São Paulo, Brazil, 2 Brazilian Paralympic Committee, Brasília, Brazil, 3 Department of Physical Education, State University of Londrina, Londrina, Brazil

The aims of this study were to estimate the magnitude of variability and progression in actual competitive and field vertical jump test performances in elite Paralympic sprinters with visual impairment in the year leading up to the 2015 Parapan American Games, and to investigate the relationships between loaded and unloaded vertical jumping test results and actual competitive sprinting performance. Fifteen Brazilian Paralympic sprinters with visual impairment attended seven official competitions (four national, two international and the Parapan American Games 2015) between April 2014 and August 2015, in the 100- and 200-m dash. In addition, they were tested in five different periods using loaded (mean propulsive power [MPP] in jump squat [JS] exercise) and unloaded (squat jump [SJ] height) vertical jumps within the 3 weeks immediately prior to the main competitions. The smallest important effect on performances was calculated as half of the within-athlete race-to-race (or test-to-test) variability and a multiple regression analysis was performed to predict the 100- and 200-m dash performances using the vertical jump test results. Competitive performance was enhanced during the Parapan American Games in comparison to the previous competition averages, overcoming the smallest worthwhile enhancement in both the 100- (0.9%) and 200-m dash (1.43%). In addition, The SJ and JS explained 66% of the performance variance in the competitive results. This study showed that vertical jump tests, in loaded and unloaded conditions, could be good predictors of the athletes' sprinting performance, and that during the Parapan American Games the Brazilian team reached its peak competitive performance.

Keywords: Paralympics, track and field, muscle power, physical disability, blind athletes

# INTRODUCTION

In general, the public is astonished by the performance of Paralympic athletes, given their extreme physical and technical capacities in spite of the presence of mild to severe physical disabilities. Although it is known that sprinting performance in Paralympic Track and Field has improved at a higher rate than the Olympic results (Grobler et al., 2015), there has been no systematic analysis of the variability and progression in competitive performance of successful teams in the months of preparation leading up to a main competition (e.g., Parapan American Games).

It has been suggested that the smallest important effect in performance at a target international event is one-half of the typical within-athlete random variability between events (Hopkins et al., 1999). An important performance progression to enhance the chances of a medal for Olympic and Paralympic swimmers in the year leading up to the main competition has been estimated to be ≈1–2% (Pyne et al., 2004; Fulton et al., 2009). In addition, in elite Olympic track athletes (including sprinters), an improvement of as little as 0.3–0.5% is considered meaningful (Hopkins, 2005). Calculating the smallest important change in Paralympic sprinters may help coaches to define targets for performance improvements in the year of preparation for the upcoming Paralympic Games.

Importantly, although the actual performance is considered the "gold standard" to assess elite athletes, simple and field based tests assessing key components of competitive outcomes can be considered as important evaluation and monitoring tools. For instance, it has been shown that loaded and unloaded vertical jumping performances are largely correlated with sprinting speed in elite sprinters (Loturco et al., 2015a,b). Confirmation of these associations between loaded/unloaded jumps (or even in combination) and sprinting performance in Paralympic athletes may help coaches to choose appropriate tests in order to evaluate and monitor Paralympic sprinters. This is particularly relevant to athletes with visual impairments as vertical jumping tests may be executed without the need for much assistance, enabling easy implementation in the training routines.

In this regard, it is important to know the within-athlete variability and progression in vertical jumping performance, to allow coaches to effectively decide whether a given change in testing performance might be considered meaningful or within the trivial variation caused by biological and/or technical factors. Based on this information, coaches can better select training strategies to optimize athletes' sports form, without necessarily assessing the actual competitive performance. Furthermore, simple tests can be used on a daily basis, thus providing fine feedback for training adjustments.

Therefore, the aim of this study was to estimate the magnitude of variability and progression in actual competitive and field vertical jump test performances in elite Paralympic sprinters with visual impairment in the year leading up to the 2015 Parapan American Games. Furthermore, we aimed to investigate the relationships between loaded and unloaded vertical jumping test results and the actual competitive sprinting performance, through the use of simple and multiple linear regression analyses.

# MATERIALS AND METHODS

Seven official competitions were analyzed (four national, two international and the Parapan American Games 2015) between April 2014 and August 2015. The competitions were sanctioned by the Brazilian Paralympic Committee (CPB), International Paralympic Committee (IPC), and Americas Paralympic Committee (APC), respectively. The physical assessments were performed close to the competitions (up to 3 weeks prior to the main competitions) in five different periods (between April 2014 and July 2015) scheduled by the High Performance Programs of CPB, as part of the athletes' monitoring during the competitive season. Fifteen Brazilian Paralympic sprinters with visual impairment, from 18 to 36 years old, took part of the study (seven men and eight women, classes: T11 [n = 9]; T12 [n = 3]; and T13 [n = 3]). All athletes were part of the permanent Brazilian team, frequently involved in national and international competitions. This elite sample comprised four world champions, two Paralympic champions, four world record holders, two Paralympic record holders, eight world medalists, 11 Paralympic medalists, 12 top-five athletes and two top-ten athletes in the 2015 world ranking, thus attesting their high level of competitiveness.

For analysis purposes, only the times attained in the finals were retained. Across the seven competitions, a total of 120 official times (68 from the 100-m and 52 from the 200-m dash) were included in the analyses. Additionally, 192 test results in the five different periods using loaded (mean propulsive power [MPP] in jump squat [JS] exercise) and unloaded (squat jump [SJ] height) vertical jumps were analyzed. All the athletes had been previously familiarized with the testing procedures. This study was approved by the Ethics Committee of the Bandeirantes Anhanguera University. Prior to study participation, all the athletes signed an informed consent form.

## Vertical Jumping Ability

Vertical jumping ability was assessed using SJ. To perform the SJ, a static position with a 90◦ knee flexion angle was maintained for 2-s before every jump attempt. No preparatory movement was allowed and an experienced researcher visually inspected for proper technique. Five attempts were performed interspersed by 15-s intervals. All attempts were executed with the hands on the hips. The jumps were performed on a contact platform (Smart Jump; Fusion Sport, Coopers Plains, Australia) with the obtained flight time (t) being used to estimate the height of the rise of the body's center of gravity (h) during the vertical jump (i.e., h = gt2 /8, where g = 9.81 m·s −2 . The best attempt was used for data analysis purposes. The athletes executed the attempts without assistance.

#### Bar Mean Propulsive Power in Jump Squat

Bar MPP in the JS exercise was assessed on a customized Smith machine (adapted by Hammer Strength, Rosemont, IL, USA). The athletes were instructed to execute three repetitions at maximal velocity for each load, starting at 40% of their body mass (BM). The athletes with visual impairment executed a knee flexion until the thigh was parallel to the ground (≈100◦

Loturco et al. Performance of Paralympic sprinters

knee angle for 2-s) and, after a command, jumped as fast as possible without losing contact between their shoulder and the bar. A load of 10% BM was gradually added in each set until a decrease in MPP was observed. A 5-min interval was provided between sets. All athletes attained their maximum values of MPP during the execution of the tests, within 4– 5 attempts. Of note, the athletes achieved their highest MPP outputs at a load corresponding to ≈100% BM. To determine MPP, a linear transducer (T-Force, Dynamic Measurement System; Ergotech Consulting S.L., Murcia, Spain) was attached to the Smith machine bar. The finite differentiation technique was used to calculate bar velocity (Sanchez-Medina et al., 2010). As Sanchez-Medina et al. (2010) demonstrated that mean mechanical values during the propulsive phase better reflect the differences in the neuromuscular potential between two given individuals, MPP rather than peak power was used in the JS. The bar maximum MPP value obtained was considered for data analysis purposes. In order to consider the differences in BM between the athletes and avoid misinterpretation of the power outputs, these values were normalized by dividing the absolute power value by the BM (i.e., relative power = W.kg−1 ) (MPP REL). All the tests were performed by the athletes with no assistance.

#### Statistical Analysis

The normality of data was confirmed using the Shapiro-Wilk test. Data are presented as means ± standard deviations (SD). The smallest important effect on performances was calculated as half of the within-athlete race-to-race (or test-to-test) variability (Hopkins et al., 1999). Additionally, the within-subject coefficient of variation (CV), with 90% confidence intervals (CI), was calculated as a measure of competitive and testing performance variability. A Pearson product-moment coefficient of correlation was used to analyze the relationships between SJ and MPP REL in the JS and sprinting time in the 100- and 200-m. The vertical jumping tests took place in close proximity to five of the seven competitions. A multiple regression analysis was performed using the vertical jump test results as predictors of 100- and 200 m dash performances. The possibility of collinearity between the predictive variables in multiple regression models was examined using variance inflation factor (VIF) and tolerance (i.e., VIF < 10 and tolerance > 0.2; Kennedy, 1992; Hair et al., 1995; Tabachnick and Fidell, 2001). Intraclass correlation coefficients (ICCs) were used to indicate the relationship within SJ and JS for, respectively, jumping height and MPP. The significance level was set as P < 0.05.

#### RESULTS

All data presented herein showed normal distribution. The VIF and tolerance values were 2.43 and 0.42, respectively, attesting that the independent variables (i.e., SJ and JS) were not collinear. The characteristics of the subjects are presented in the **Table 1**. The BM of the athletes did not vary substantially across the five evaluation moments (varying from 61.41 ± 9.76 to 63.84 ± 10.66). **Figure 1A** displays the means of the 100-m dash performances in the seven competitions. The mean CV (90% CI) over the competitions was 1.79% (1.47; 2.24). Meanwhile, **Figure 1B** depicts the mean performance in the 200-m events. The mean CV (90% CI) across the seven competitions was 1.35% (0.83; 1.88). The performance variation in the SJ and JS over the five moments is displayed in **Figures 2A,B**, respectively. Importantly, the ICC was 0.94 for the SJ and 0.92 for the loaded JS. The mean CVs (90% CI) for SJ and JS were 5.58% (4.18; 6.99) and 7.97% (5.91; 10.02), respectively.

The correlations (90% CI) between SJ and JS test results and 100- and 200-m dash performances were −0.80 (−0.71; −0.88) and −0.71 (−0.61; −0.81) for SJ and JS with 100-m, respectively, and; −0.81 (−0.72; −0.89) and −0.65 (−0.48; −0.79) for SJ and JS with 200-m, respectively (P < 0.01 for all correlations; **Figure 3**). The multiple regression analysis using SJ and JS test results as predictors of 100- and 200-m dash performances is presented in **Table 2**. The SJ and JS explained 66% of the performance variance in both 100- and 200-m dash performances.

#### DISCUSSION

This is the first study to investigate the relationships between loaded/unloaded vertical jump tests and the actual performance obtained by top-level Paralympic sprinters in 100 and 200 m dash events. The main finding reported herein is that, providing they are executed only a few weeks before the official tournaments (i.e., from 1 to 3 weeks), SJs and loaded JSs—when combined in a multiple linear regression model—can be good predictors of the actual competitive performance of top-level athletes with visual impairment. In addition, during a given training period, the dynamics of the performance in these specific jump tests seem to be analogous to the dynamics of the actual results obtained in 100 and 200 m dash events.

Another study has already reported strong correlations between sprinting performance (i.e., measured in time) and SJ height (r = −0.82) in elite sprinters who compete in 100 m dash events (Loturco et al., 2015b). This "close relationship" can be explained when analyzing the mechanical aspects of unloaded SJs. In order to jump higher, an athlete has to apply a substantial amount of force against the ground—and against his/her own BM (Loturco et al., 2015a,b). Thus, this measurement is already normalized by the subject's weight, being able to express his/her relative neuromuscular potential (i.e., relative values of muscle force and muscle power; Bosco et al., 1983; Copi et al., 2014). Furthermore, from a mechanical perspective, athletes with better performances in vertical jumps are possibly more efficient at overcoming the inertia and accelerating their bodies vertically (Bunton et al., 1993; Loturco et al., 2015b). Importantly, as the ground reaction forces increase, the vertical jump height increases (Loturco et al., 2015b). The same occurs in sprinting, during the transition from lower to higher velocities

Committee; ParaPan corresponds to the ParaPan American Games.

(i.e., top-speed sprinting), which results in shorter support phases with simultaneous increases in vertical peak force (Nilsson and Thorstensson, 1989). Curiously, even in sprinters with visual impairment, this mechanical similarity seems to be capable of influencing the specific performance in 100 and 200 m dash events. Certainly, the user-friendly characteristic and practicality of SJ facilitates its execution by athletes with visual impairment, thus reinforcing its use as a tool to control/monitor the variation in sprinting performance presented by this specific group of Paralympics.

Loaded JSs are usually performed with moderate training loads, moved as rapidly as possible (Cormie et al., 2011; Loturco et al., 2015d). In this study, the athletes executed an optimal loading test in order to determine their individual optimal power loads (i.e., loads capable of generating higher values of muscle power). The maximal JS power has been extensively related to a variety of specific sports measures, including speed and acceleration abilities (Sleivert and Taingahue, 2004; Cronin and Hansen, 2005; Loturco et al., 2015a,b,d). Interestingly, the athletes also presented significant correlations between MPP and actual sprinting time, both in 100 and 200 m dash events (r = −0.71 and −0.65, for 100- and 200-m). Of note, the athletes reached their highest MPP at ≈100% of their BM, which represents a substantial amount of external overloading. At this loading condition, movement performance is possibly associated with maximum dynamic strength (i.e., ability to apply high force at low velocity; Baker and Nance, 1999; Young et al., 2001; Stone et al., 2003). Similarly, to start from

zero-velocity and achieve higher accelerations in very-short periods, the athletes have to apply greater amounts of force (at lower velocities) against the ground (Wisløff et al., 2004; Loturco et al., 2014). More importantly, based on the parametric relationship between force and velocity (Cronin et al., 2002; Loturco et al., 2015c), these higher rates of acceleration can only be attained if the accelerated mass (i.e., athlete's BM) represents a relatively low resistance for the athlete involved (when compared to his/her maximum dynamic strength; Moss et al., 1997; Cormie et al., 2007; Loturco et al., 2014). Therefore, although we did not have the "partial times" of the actual competitions to perform additional correlational analysis in this study, it is highly conceivable that the more powerful athletes presented superior performance in the acceleration phases of sprinting, in both the 100 and 200 m dash. Undoubtedly, this issue should receive priority in future investigations, in spite of the difficulty in obtaining partial times in official competitions.

In this study, the possibility of combining two independent variables (i.e., SJ and JS) in a multiple linear regression model to more accurately predict the athletes' actual performance was considered due to the distinct importance of each one of these measures in sprinting mechanics and due to the high levels of competitiveness found in Paralympic track and field competitions. As aforementioned, whereas JS is probably more related to the accelerating phases of sprinting (Wisløff et al., 2004; Loturco et al., 2014), SJ may be more associated with the "top-speed" phases of both the 100- and 200-m dash (Loturco et al., 2015b). Therefore, since individual performance in toplevel sports depends on very fine adjustments, it is worth considering novel and better models/strategies to predict results and enhance performance. Still, although the use of multiple

regression models have increased only (on average) ∼1.2% of the explained variance between dependent (actual sprint times) and independent variables (SJ and JS), we considered relevant to carry out this calculation, since slight differences between individuals in 100- and 200-m dash events might significantly affect their competitive results. Observing the data reported here, from this point on, Paralympic coaches can better estimate the actual performance of their top-level athletes in official sprint competitions. Furthermore, by understanding the importance of this specific "mechanical combination" (i.e., SJ and JS) in sprinting performance, they will be able to develop more effective and specific training programs.

Concerning the within-subject variability, the smallest worthwhile enhancements in the 100- (0.9%) and 200-m dash (1.43%) were comparable to those reported in Olympic and Paralympic swimmers (Pyne et al., 2004). However, these values were higher than the estimates provided by elite track athletes without disabilities (Hopkins, 2005). The greater variability in athletes with visual impairment's performances may be associated with their disabilities (Fulton et al., 2009) and the possible influence of their respective guides on the individuals' sprinting mechanics (unpublished data). Importantly, the smallest worthwhile enhancement provides the coach with an idea of the meaningfulness of a given change in an athlete's performance. In general, an enhancement needs to be higher than the smallest worthwhile enhancement to affect the results

SJ, squat jump; JS, jump squat; \*P < 0.01.

(i.e., medal prospects; Fulton et al., 2009). Curiously, in the 100-m dash, the athletes presented worse sprinting times than their mean times during the period of observation, but during the Parapan American Games they achieved their "performance peak." Although in the 200-m the times were close to the mean performance throughout the observation, during the Parapan American Games, they reached a meaningful performance change (in comparison to the previous analyzed competitions). To some extent, this explains the outstanding results obtained by the Brazilian team during the 2015 Pan American Games (three gold, six silver, and two bronze medals in the 100- and 200-m races).

The jumping test results were substantially more variable than the actual competitive performances in the 100- and 200-m dash (CV of SJ = 5.58% and JS = 7.97%), which implies the need for larger improvements in jumping tests, in order to consider these enhancements as meaningful. The general dynamics of the vertical jumping performance were similar to the sprinting performance; nevertheless, only SJ (change > 2.79%) attained a meaningful enhancement prior to the Parapan American Games. Accordingly, while monitoring SJ and JS in Paralympic athletes, coaches need to be aware that the meaningful performance changes should be greater than ≈2.79–3.98%; smaller changes can be considered within the range of the inherent measurement variability. The advantage of these practical and timesaving tests is that they can be easily implemented in the athletes' routines, for finely adjusting the training strategies and, therefore, improving sprinting performance (e.g., stretch-shortening cycle efficiency).

Future studies are necessary in order to determine other factors involved in the non-explained variance of sprinting ability in athletes with visual impairment (e.g., anthropometric characteristics of the subjects and coordination between the athletes with visual impairment and their respective guides, etc). Possibly, some factors related to jumping and running mechanics will reveal more movement similarities and additional associations between their respective kinetic and kinematic parameters.

## REFERENCES

#### CONCLUSION

Performance in Paralympic elite sprinting depends on a series of neuromuscular, physiological and technical factors. This study showed that vertical jump tests, in loaded and unloaded conditions, could be good predictors of athletes' sprinting performance, mainly when combined in a multiple linear regression equation. Furthermore, in this specific group of toplevel Paralympic athletes, the dynamics of SJ and JS performances seem to follow the same variation as 100- and 200-m actual times. These findings may have important implications in athletes with visual impairment's training and testing methodology, since vertical jump tests can be easily performed by subjects with total or partial visual impairments. In addition, Paralympic track and field coaches can use these simple field assessments to specifically monitor their elite athletes close to official competitions, adjusting the training contents in order to optimize each athlete's performance peak. Finally, further studies should be conducted to investigate the chronic effects of training athletes with visual impairment using exclusively loaded and unloaded vertical jumps.

performance of dynamic and static weighted jumps. J. Strength Cond. Res. 17, 140–147.

**Conflict of Interest Statement:** The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2015 Loturco, Winckler, Kobal, Cal Abad, Kitamura, Veríssimo, Pereira and Nakamura. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

# Individualized Internal and External Training Load Relationships in Elite Wheelchair Rugby Players

#### Thomas A. W. Paulson\*, Barry Mason, James Rhodes and Victoria L. Goosey-Tolfrey

The Peter Harrison Centre for Disability Sport, School of Sport, Exercise and Health Sciences, Loughborough University, Loughborough, UK

Aim: The quantification and longitudinal monitoring of athlete training load (TL) provides a scientific explanation for changes in performance and helps manage injury/illness risk. Therefore, accurate and reliable monitoring tools are essential for the optimization of athletic performance. The aim of the present study was to establish the relationship between measures of internal [heart rate (HR) and session RPE (sRPE)] and external TL specific to wheelchair rugby (WR).

#### Edited by:

Davide Malatesta, Université de Lausanne, Switzerland

#### Reviewed by:

Melissa L. Bates, University of Wisconsin–Madison, USA Gianluca Vernillo, University of Milan, Italy Matthew Weston, Teesside University, UK

> \*Correspondence: Thomas A. W. Paulson<EMAIL_ADDRESS>
#### Specialty section:

This article was submitted to Exercise Physiology, a section of the journal Frontiers in Physiology

Received: 28 August 2015 Accepted: 30 November 2015 Published: 21 December 2015

#### Citation:

Paulson TAW, Mason B, Rhodes J and Goosey-Tolfrey VL (2015) Individualized Internal and External Training Load Relationships in Elite Wheelchair Rugby Players. Front. Physiol. 6:388. doi: 10.3389/fphys.2015.00388

Methods: Fourteen international WR athletes (age = 29 ± 7 years; body mass = 58.9 ± 10.9 kg) were monitored during 18 training sessions over a 3 month period during the competitive phase of the season. Activity profiles were collected during each training session using a radio-frequency based indoor tracking system (ITS). External TL was quantified by total distance (m) covered as well as time spent and distance covered in a range of classification-specific arbitrary speed zones. Banister's TRIMP, Edwards's summated HR zone (SHRZ), and Lucia's TRIMP methods were used to quantify physiological internal TL. sRPE was calculated as the product of session duration multiplied by perceived exertion using the Borg CR10 scale. Relationships between external and internal TL were examined using correlation coefficients and the 90% confidence intervals (90% CI).

Results: sRPE (r = 0.59) and all HR-based (r > 0.80) methods showed large and very large relationships with the total distance covered during training sessions, respectively. Large and very large correlations (r = 0.56 − 0.82) were also observed between all measures of internal TL and times spent and distances covered in low and moderate intensity speed zones. HR-based methods showed very large relationships with time (r = 0.71 − 0.75) and distance (r = 0.70 − 0.73) in the very high speed zone and a large relationship with the number of high intensity activities (HIA) performed (r = 0.56−0.62). Weaker relationships (r = 0.32−0.35) were observed between sRPE and all measures of high intensity activity. A large variation of individual correlation co-efficient was observed between sRPE and all external TL measures.