Submitted 4 January 2023
Accepted 20 March 2023
Published 17 April 2023
Corresponding author
Małgorzata Pałac,
malgorzatapalac3@gmail.com
Academic editor
Mike Climstein
Additional Information and
Declarations can be found on
page 11
DOI 10.7717/peerj.15214
Copyright
2023 Pałac et al.
Distributed under
Creative Commons CC-BY 4.0
OPEN ACCESS
Relationship between respiratory muscles
ultrasound parameters and running
tests performance in adolescent football
players. A pilot study
Małgorzata Pałac1,2, Damian Sikora1, Tomasz Wolny1,2 and Paweł Linek1,2
1 Musculoskeletal Elastography and Ultrasonography Laboratory, Institute of Physiotherapy and Health
Sciences, The Jerzy Kukuczka Academy of Physical Education, Katowice, Śląskie, Poland
2 Musculoskeletal Diagnostic and Physiotherapy - Research Team, The Jerzy Kukuczka Academy of Physical
Education, Katowice, Poland
ABSTRACT
Purpose. Assessing the relationship between ultrasound imaging of respiratory muscles
during tidal breathing and running tests (endurance and speed) in adolescent football
players.
Methods. Ultrasound parameters of the diaphragm and intercostal muscles (shear
modulus, thickness, excursion, and velocity), speed (30-m distance), and endurance
parameters (multi-stage 20-m shuttle run test) were measured in 22 male adolescent
football players. The relation between ultrasound and running tests were analysed by
Spearman’s correlation.
Results. Diaphragm shear modulus at the end of tidal inspiration was moderately
negatively (R = −0.49;p = 0.2) correlated with the speed score at 10 m. The diaphragm
and intercostal muscle shear modulus ratio was moderately to strongly negatively
correlated with the speed score at 10 m and 30 m (about R = −0.48;p = 0.03).
Diaphragm excursion was positively correlated with the speed score at 5 m (R =
0.46;p = 0.04) and 10 m (R = 0.52;p = 0.02). Diaphragm velocity was moderately
positively correlated with the speed score at 5 m (R = 0.42;p = 0.06) and 30 m (R =
0.42;p = 0.07). Ultrasound parameters were not significantly related to all endurance
parameters (R ≤ 0.36;p ≥ 0.11).
Conclusions. Ultrasound parameters of the respiratory muscles are related to speed
score in adolescent football players. The current state of knowledge does not allow us
to clearly define how important the respiratory muscles’ ultrasound parameters can be
in predicting some performance parameters in adolescent athletes.
Subjects Kinesiology, Sports Medicine
Keywords Athlete, Ultrasonography, Motor skills, Respiration, Diaphragm, Intercostal muscle
INTRODUCTION
It is well known that respiratory function is related to physical activity and affects exercise
performance in athletes. Respiratory muscles (RMs) are an integral part of the respiratory
system and physical activity. Their morphology and contractile properties make them
useful in endurance types of training (Welch, Kipp & Sheel, 2019). RMs are susceptible to
How to cite this article Pałac M, Sikora D, Wolny T, Linek P. 2023. Relationship between respiratory muscles ultrasound parameters and
running tests performance in adolescent football players. A pilot study. PeerJ 11:e15214 http://doi.org/10.7717/peerj.15214
fatigue, resulting in reduced performance (Aliverti, 2016; Welch, Kipp & Sheel, 2019) and
insufficient oxygen supply to the working muscles (Mcconnell & Lomax, 2006). Studies
have shown that RMs training improves RMs’ parameters and decreases muscle fatigue,
resulting in a change in respiratory system function (Welch, Kipp & Sheel, 2019). It is also
indicated that inspiratory muscle training affects the test results involving time trials or
exercise endurance time (Hajghanbari et al., 2013). The main RMs are the diaphragm
(DA) and intercostal muscles (IMs). Physiologically, the DA executes about 65% of the
respiratory work during inspiration (Moeliono, DM & Nashrulloh, 2022) and affects to a
greater extent lung movements (Welch, Kipp & Sheel, 2019). IMs, in turn, contribute to
chest expansion (Yoshida et al., 2021), leading to increased inspiratory volume (Yoshida et
al., 2019). During inspiration, while the IMs contract, the abdominal muscles gradually
relax, and vice versa during expiration. This mechanism has some effects: (a) it prevents
rib cage distortion; (b) the DA is unloaded and can act as a flow generator; and (c) the
abdominal volume decreases below resting levels (Aliverti, 2016).
In football, RM training improves RMs’ strength, which helps to improve exercise
tolerance and lower blood lactate levels (Guy, Edwards & Deakin, 2014). Respiration
exercises also improve muscle oxygen supply during high-intensity exercise (Archiza et
al., 2018). This process can be translated into an improvement in fatigue tolerance and
running efficiency of football players (Archiza et al., 2018). Additionally, it was confirmed
that in youth football players, the RMs improve aerobic endurance, which is one of the
most important parameters of motor preparation in football (Mackała et al., 2020).
Spirometry, as a gold standard of assessing respiratory function (Durmic et al., 2015),
allows reproducible and standardised assessment of pulmonary function (Lazovic-Popovic
et al., 2016). However, spirometry performance is the result of many factors (including
airway obstruction, respiratory compliance, and RM strength) that do not allow direct
analysis of the RMs (Pałac et al., 2022). In contrast, ultrasound (US) imaging can directly
and reliably assess the thickness, excursion, and shear modulus (elasticity) of the RMs
(Pałac et al., 2022 ; Zhu et al., 2019). Pałac et al. (2022) also confirmed the reliability of
RMs US measurements in adolescent football players. In the literature, some studies have
shown the relationship between US parameters of the RMs and spirometry parameters
in different populations (Pałac & Linek, 2022). However, a recent systematic review by
Pałac & Linek (2022) has shown that the relationship between US parameters and lung
function (measured, for example, by spirometry) is inconclusive. Thus, the two methods of
measurement should not be used interchangeably, as they measure different aspects (Pałac
& Linek, 2022).
Taking into account that RMs training affects motor skills and has implications for
sports training, it is worth considering these muscles in athletes. Running tests are usually
used to assess motor skills such as speed and endurance. According to the literature,
speed and endurance depend on the thickness of the lower-extremity muscles, which
has been measured using US in young athletes (Stock et al., 2017). Other US parameters
have been related to motor skills in elite sports (Sarto et al., 2021). For example, RMs
function correlates with postural stability in footballers (León-Morillas et al., 2021), and
thus potentially affects motor skills as well. To the best of our knowledge, however, there
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have been no studies relating US measurements of RMs with motor skills (endurance and
speed) in adolescent football players. We believe that such an analysis is justified, as it may
launch the exploration of RMs US measurements that are potentially useful in predicting
motor skill performance in athletes. The aim of this preliminary report was to assess the
relationship between US of RMs during tidal breathing and selected motor skill (endurance
and speed) performance in adolescent football players. Based on the current state of the art,
we hypothesised that endurance and speed parameters should be related to the thickness
and elasticity of RMs (DA and IMs) in adolescent football players.
MATERIALS & METHODS
Informed consent
The study was approved by the Ethics Committee of the Jerzy Kukuczka Academy of
Physical Education in Katowice (Decision No. 9/2020) and conducted in accordance with
the guidelines of the Declaration of Helsinki. Before the study, participants and their
parents were informed about all procedures performed and have given written consent to
participate. All participants provided written informed consent to participate in the study.
This research did not receive any external funding.
Setting and study design
US data were collected in a laboratory setting (Institute of Physiotherapy and Health
Sciences, Musculoskeletal Elastography and Ultrasonography Laboratory) by two
physiotherapists, whereas endurance and speed measurements were performed by a
motor preparation assistant on a football field with an artificial ground surface. Speed and
endurance tests were conducted during two consecutive training days. During the first day,
speed tests were performed, and on the next day, an endurance test was conducted. All
measurements were performed in a preparation phase for the next football season. Due to
organisational issues, US was collected one week after the endurance measurements.
Participants
Adolescent footballers from the professional football academy were considered for the
study. We invited all male individuals from a randomly selected team (one age group).
The basic criteria of eligibility for the study were (a) all players had to be free of any health
or injury issues at the time of testing; (b) no respiratory-related medical history; and (c)
no surgical procedure on the pectoral chest, abdominal cavity, pelvic girdle, and/or spine.
Information regarding the athletes’ health was obtained by a short interview with the
footballers and a coach or physiotherapist working with these athletes in the club.
Ultrasound measurements
All US measurements were collected by an Aixplorer US scanner (Product Version 12.2.0,
Software Version 12.2.0.808; Supersonic Imagine, Aix-en-Provence, France). Linear
transducer array (2–10 MHz; SuperLinear 10-2, Vermon, Tours, France) in the SWE
mode was used to evaluate the shear modulus and thickness of the ICs and DA on the
right side of the body. Each participant laid in the supine position with the right hand
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Figure 1
Illustration showing the ultrasound probe placement and orientation (parallel to the ribs).
Full-size
DOI: 10.7717/peerj.15214/fig-1
placed under the head in order to better visualise the DA. At the beginning, anterior and
mid-axillary lines were marked on the participant’s chest, and the US probe was positioned
between the lines (Fig. 1). The probe was positioned in the first intercostal space (counting
from the bottom) where the lungs did not obscure the DA during tidal breathing. The US
measurements were performed in a longitudinal probe position (parallel to the ribs). The
participants were asked to relax and breath quietly throughout the procedure. US data
were collected twice at the end-tidal inspiration and at the end-tidal expiration, separately.
The reliability of RM measurements has been confirmed in previous studies on healthy
adolescent football players (Pałac & Linek, 2022).
DA excursion was collected in the M-mode on the Aixplorer US scanner coupled with
convex transducer array (1–6 MHz, Cristal Curved XC6-1; Vermon, Tours, France). For
the excursion measurement, the participant was in the supine position with the upper limbs
along the trunk. The probe was placed in the right subcostal area. The participant was asked
to take a maximal inspiration and then quietly expire. For the excursion DA measurement,
a video collecting the work of breathing before maximal inspiration (tidal expiration)
and during maximal inspiration and tidal expiration was recorded. The reliability of DA
excursion was confirmed on athletes (Calvo-Lobo et al., 2019). DA excursion amplitude
was described as the upright perpendicular distance from the minimum to the maximum
point of DA displacement during a given breathing manoeuvre. DA excursion velocity is
described as the velocity of DA displacement (during a given breathing pattern).
Shear modulus and thickness were calculated from the US images. The Q-Box™
quantitative tool was used to quantify muscle shear modulus. Three separate circles were
positioned inside the fascial edge of each muscle, and the shear modulus was automatically
calculated. The images were then saved on an external drive in DICOM format and
transferred to a computer, where the muscle thickness was measured using RadiAnt
DICOM Viewer (Medixant, Poznań, Poland). The DA thickness was measured between
the pleural and peritoneal lines. The ICs were measured as the first more superficial
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muscle than the DA. The thickness and shear modulus ratio was also measured as the
end-inspiratory US value divided by the end-expiratory US value.
Running tests
Two running tests were used to analyse the participants‘ endurance and speed. All
measurements were collected by using photocells of the Witty System (Microgate Bolzano,
Italy) with an accuracy of 0.01 s. The Witty System was coupled with Witty Manager
(1.14.32 version; Microgate Bolzano, Italy) and connected to a laptop, allowing data
collection (Altmann et al., 2019). Both tests were performed on a dry grass football pitch
on a sunny day, and the participants wore football kit and boots.
Endurance was assessed by a progressive, multi-stage 20-m shuttle run test (MSRT)
as a modification of the beep test (Green et al., 2013). The beep test requires athletes to
run back and forth (‘‘shuttle’’) between two cones separated by 20 m. The initial speed
was 2.22 m/s for 1 min. At the end of the first min, the speed increased to 2.5 m/s and
progressively increased by 0.14 m/s each min thereafter. The speed was imposed by audible
beeps from pre-recorded audio. Each min stage (level) consisted of multiple ‘‘shuttles’’,
and the number depended on the stage speed. Participants were advised to keep running
at the pace of the beeps for as long as possible. Once the participant could no longer
keep pace with the beeps (i.e., failed to complete two consecutive shuttles in time), the
test was terminated (Green et al., 2013). For the purpose of the study, we calculated the
parameter ‘‘Total’’ as the total number of completed 20-m repetitions (during the whole
test). The following parameters were used for further analysis: Total and calculated VO2max
(ml · kg−1· min−1). VO2max was estimated from the maximal speed attained during the test
via the previously developed prediction equation −24.4+6.0× maximum aerobic speed
(sec) (Léger et al., 1988).
The speed test involved running 30 m as fast as possible in a straight line between the
photocells. Before the test began, the participants stood adjacent to (i.e., their toes were
not touching) the starting line in a standing split-stance position. They were instructed to
run as fast as possible and slow down after crossing the finish line. A sound signal marked
the beginning of each test. The timer was switched on when the starting line was passed,
and measurements were automatically taken at 5 m, 10 m, and 30 m by the photocells
positioned at those distances. The timer stopped when the finishing line was passed. Each
participant ran the course twice, and the mean scores from both were analysed (Altmann
et al., 2019).
Statistical analysis
Data were analysed using Statistica 13.1 PL (Statsoft, Tulsa, OK, USA) and Excel (Microsoft
Corporation, USA) software. Due to the non-normality of the distribution in the Shapiro–
Wilk test, we decided to use Spearman’s correlation in the analysis. The correlation value
(R) was interpreted as follows: 0 to 0.30 or 0 to −0.30 was considered a weak correlation;
0.31 to 0.50 or −0.31 to −0.50 a moderate correlation; 0.51 to 0.70 or −0.51 to −0.70
a strong correlation; and 0.71 to 1 or −0.71 to −1 a very strong correlation (Hopkins et
al., 2009). The significance level was set at p ≤ 0.05. For the a priori analysis, the sample
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Figure 2
Flow chart.
Full-size
DOI: 10.7717/peerj.15214/fig-2
size was determined using G*POWER (Version 3.1.9.7; Universität Kiel, Kiel, Germany)
using an alpha of 0.05, a power of 0.80, and an effect size of 0.50 for a two-tailed test.
Because Spearman’s rank correlation coefficient is computationally identical to Pearson’s
product-moment coefficient, we used the software to calculate the latter.
RESULTS
Participants
Based on the assumptions, the required sample size was determined to be 26. Out
of 30 initially invited footballers, 24 met the inclusion criteria. However, during the
measurements, two athletes were at a camp with the senior team. Thus, a total of 22
adolescent footballers (two goalkeepers, eight defenders, nine midfielders, three forwards)
were included in the final analysis (Fig. 2). Basic data and all parameters measured are
shown in Table 1.
Speed test vs US
DA shear modulus at the end of tidal inspiration was moderately negatively correlated with
the speed score at 10 m. The DA shear modulus ratio was moderately negatively correlated
with the speed score at 10 m and 30 m. The IC shear modulus ratio was moderately
negatively correlated with the speed score at 10 m and strongly negatively correlated with
the speed score at 30 m. Additionally, DA excursion was positively correlated with the
speed score at 5 m (moderate) and 10 m (strong). DA velocity was moderately positively
correlated with the speed score at 5 and 30 m, but statistical significance was borderline
(p = 0.06). Detailed R values for each correlation are presented in Table 2.
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Table 1
Experimental group characteristics: anthropometric data, ultrasound parameters, endurance
test (multi-stage 20-m shuttle run test), and speed test (straight line speed in 5, 10, and 30 m).
Characteristic (n = 22)
mean ± SD
median
Anthropometric data
Age (yr)
17.1 ± 0.29
17.0
Body mass (kg)
71.4 ± 7.74
70.0
Body height (cm)
180 ± 5.76
180
BMI (kg/m2)
22.1 ± 1.95
22.0
Football practice (yr)
7.77 ± 0.75
8.0
SWE - Shear modulus (kPa)
Diaphragm at the end of tidal inspiration
31.2 ± 6.26
31.5
Diaphragm at the end of tidal expiration
29.4 ± 5.60
27.9
Diaphragm ratio
1.07 ± 0.18
1.05
Intercostal muscle at the end of tidal inspiration
27.1 ± 6.23
26.6
Intercostal muscle at the end of tidal expiration
27.0 ± 6.00
25.7
Intercostal muscle ratio
1.01 ± 0.15
0.97
B-mode –Thickness (mm)
Diaphragm at the end of tidal inspiration
2.09 ± 0.85
1.82
Diaphragm at the end of tidal expiration
1.71 ± 0.59
1.48
Diaphragm ratio
1.21 ± 0.21
1.20
Intercostal muscle at the end of tidal inspiration
3.98 ± 0.85
4.05
Intercostal muscle at the end of tidal expiration
4.09 ± 0.89
3.97
Intercostal muscle ratio
0.99 ± 0.15
0.95
M-mode
Diaphragm excursion (cm)
4.73 ± 1.45
4.59
Diaphragm velocity (cm/s)
2.13 ± 0.89
1.83
Multi stage 20-m shuttle run test
Total
127 ± 13.2
122
calculated VO2max (ml · kg−1 ·min−1)
56.2 ± 3.54
55.1
Speed test (s)
Distance 5 m
1.03 ± 0.05
1.03
Distance 10 m
1.87 ± 0.52
1.77
Distance 30 m
4.19 ± 0.20
4.14
Notes.
SD, standard deviation; BMI, Body Mass Index; SWE, shear wave elastography; ratio, diaphragm at the end of tidal inspi-
ration/diaphragm at the end of tidal expiration; Total, total number of completed 20-m repetitions.
MSRT vs US
US parameters were not significantly related to endurance parameters, although
correlations varied from weak to moderate. Detailed R values for each correlation are
presented in Table 3.
DISCUSSION
The preliminary report was designed to assess the relationship between US of RMs
during tidal breathing and selected motor skill (endurance and speed) performance
in adolescent football players. To the best of our knowledge, there has not yet been a
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Table 2
Correlations between ultrasound parameters and speed test results.
5 m
10 m
30 m
R
p
R
p
R
p
Shear modulus
Diaphragm at the end of tidal inspiration
−0.34
0.12
−0.49
0.02*
−0.24
0.29
Diaphragm at the end of tidal expiration
−0.10
0.66
−0.14
0.55
0.10
0.66
Diaphragm ratio
−0.31
0.16
−0.48
0.02*
−0.41
0.06
Intercostal muscle at the end of tidal inspiration
−0.26
0.26
−0.39
0.08
−0.18
0.44
Intercostal muscle at the end of tidal expiration
−0.13
0.58
−0.16
0.49
0.16
0.48
Intercostal muscle ratio
−0.28
0.22
−0.47
0.03*
−0.54
0.01*
Thickness
Diaphragm at the end of tidal inspiration
−0.07
0.75
−0.06
0.80
0.22
0.34
Diaphragm at the end of tidal expiration
−0.27
0.23
−0.12
0.60
0.25
0.25
Diaphragm ratio
0.33
0.13
0.07
0.75
−0.03
0.91
Intercostal muscle at the end of tidal inspiration
−0.19
0.42
−0.07
0.78
0.11
0.63
Intercostal muscle at the end of tidal expiration
−0.08
0.74
−0.11
0.64
0.05
0.83
Intercostal muscle ratio
−0.04
0.86
0.14
0.56
0.07
0.76
M-mode
Diaphragm excursion
0.46
0.04*
0.52
0.02*
0.26
0.27
Diaphragm velocity
0.42
0.06
0.34
0.15
0.42
0.07
Notes.
SWE, shear wave elastography.
*statistically significant p < 0.05.
R, correlation coefficient; p, probability value; ratio, diaphragm at the end of tidal inspiration/diaphragm at the end of tidal expiration.
study relating the shear modulus, thickness, excursion, and velocity of the DA and ICs
with parameters of speed and aerobic endurance based on MSRT in adolescent football
players. This preliminary study has shown that US of RMs measurements (shear modulus,
thickness, excursion, velocity) corresponded to speed in adolescent athletes. Thus, our
initial hypothesis was partially confirmed because footballers with higher values of DA
shear modulus at the end of tidal inspiration obtained better results in the 10-m speed test.
Similarly, a higher DA and IC shear modulus ratio corresponded to a better speed score at
10 and 30 m, and a higher value of DA excursion and velocity was related to worse scores
during the speed test. In turn, our results rejected the hypothesis that RMs are related to
endurance in adolescent footballers.
Speed
Taking all the results together, our study shows that RM shear modulus during tidal
breathing may be partially related to the speed score in adolescent footballers. The shear
modulus value is related to passive muscle force (Koo & Hug, 2015) and can be used to
estimate changes in muscle force (Ate¸s et al., 2015). Chino et al. (2018) showed that DA
shear modulus is non-linearly related to inspiratory mouth pressure, increasing rapidly at
low inspiratory mouth pressure levels, but less rapidly as mouth pressure reaches higher
levels. It can therefore be stated that a higher value of the DA shear modulus indicates greater
inspiratory muscle strength. Another study confirmed that DA stiffness increases during
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Table 3
Relationship between ultrasound parameters and endurance test (multi-stage 20-m shuttle
run) results.
Total
VO2max
R
p
R
p
Shear modulus
Diaphragm at the end of tidal inspiration
−0.16
0.49
0.07
0.76
Diaphragm at the end of tidal expiration
−0.17
0.46
−0.05
0.83
Diaphragm ratio
0.03
0.88
0.18
0.42
Intercostal muscle at the end of tidal inspiration
0.03
0.90
0.33
0.15
Intercostal muscle at the end of tidal expiration
−0.05
0.84
0.17
0.47
Intercostal muscle ratio
0.18
0.43
0.32
0.16
Thickness
Diaphragm at the end of tidal inspiration
0.01
0.98
0.17
0.45
Diaphragm at the end of tidal expiration
0.10
0.66
0.29
0.18
Diaphragm ratio
−0.14
0.53
−0.12
0.59
Intercostal muscle at the end of tidal inspiration
0.20
0.40
0.36
0.11
Intercostal muscle at the end of tidal expiration
−0.01
0.97
0.10
0.66
Intercostal muscle ratio
0.16
0.48
0.25
0.27
M-mode
Diaphragm excursion
0.19
0.41
−0.03
0.91
Diaphragm velocity
0.20
0.41
0.17
0.49
Notes.
SWE, shear wave elastography; Total, total number of completed 20-m repetitions; VO2max, calculated VO2max (ml · kg−1 ·
min−1); R, correlation coefficient; p, probability value; ratio, diaphragm at the end of tidal inspiration/diaphragm at the
end of tidal expiration.
inspiration (Şendur et al., 2022). Our study shows that a stiffer (higher shear modulus
value) DA during tidal inspiration characterised athletes with a better score in the speed
test. This may indicate that a stiffer DA improves speed performance.
The DA shear modulus value is also related to transdiaphragmatic pressure (Bachasson
et al., 2018), which is considered the gold standard for DA examination (Ricoy et al., 2019).
Transdiaphragmatic pressure is the main measurement for determining DA strength
(Hamnegard et al., 1995) and is clinically relevant because it represents the actual force that
drives changes in lung volume and therefore ultimately alveolar ventilation (Bachasson
et al., 2018). Sprint running (up to 6 s/up to 40 m) is characterised by anaerobic effort
(Sanders et al., 2017). In our study, therefore, it can be assumed that the athletes had an
anaerobic effort at the 30-m distance, so they were running at apnoea. It has been suggested
that there is increased chest pressure during the initial phase of the speed test, which is
linked to the Valsalva test (Turban, 2010). The Valsalva manoeuvre initiates with deep
inhalation and DA downward movement (Talasz et al., 2012). Thus, the DA seems to be
the main muscle involved in the Valsalva manoeuvre. The increased DA shear modulus
during tidal breathing may predispose to a stronger DA contraction during the speed trial,
resulting in a better score in the initial phase of running.
At a distance of 30 m, the DA and IC shear modulus ratio seems to be more significant.
The ratio is calculated by dividing the shear modulus value at the peak of tidal inspiration
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by the shear modulus value at the peak of tidal expiration. In our study, the higher the DA
and IC shear modulus ratio, the better the speed test score. The ratio score is therefore
determined not only by the shear modulus value during inspiration but also during
expiration. This means that the best speed scores were achieved by athletes who had a
higher RM shear modulus value during tidal inspiration and simultaneously a lower RM
shear modulus value during tidal expiration. It may be that a better ability to relax the RMs
allows for their greater contraction. When a muscle lengthens, the muscle spindle located
inside the muscle is stretched, causing the muscle fibres to contract (Bhattacharyya, 2017).
In turn, the comparable correlation values between each of the RMs and speed is probably
due to the similar function of the DA and ICs. These muscles both affect chest movement
(Ratnovsky, Elad & Halpern, 2008), produce axial rotations of the thorax (Whitelaw et al.,
1992), and are important respiratory pump muscles (Han et al., 1993). Consequently, their
work must be coordinated (Han et al., 1993). In addition, although the DA is the main
RM, when the respiratory workload increases (high breathing efforts), the activity of ICs
plays an important role (Ratnovsky, Elad & Halpern, 2008).
In view of the previous considerations, it is difficult to explain why footballers
characterised by greater DA excursion and velocity during maximal inspiration had worse
running scores. It was assumed that the increased stiffness of the DA during tidal breathing
allowed greater stiffness of the DA during the Valsalva test because greater stiffness may
result in lower DA excursion and velocity. Unfortunately, there are no studies connecting
US assessment of RMs to speed in athletes, which greatly limits the interpretability of these
preliminary findings.
Endurance
Some studies have shown that exercises involving the RMs improve endurance by reducing
energy demand (Bahenský et al., 2021) and increase aerobic tolerance (Mackała et al.,
2020) in youth athletes. It has also been indicated that breathing technique can affect
endurance through reduced respiratory work and delayed RM fatigue (Bahenský et al.,
2021). This was the reason we hypothesised that endurance should be related to US of RMs
in our study. This was not confirmed, as there was no relationship between the endurance
and US parameters of RMs. In cited studies (Bahenský et al., 2021; Mackała et al., 2020),
RMs strength was measured indirectly by analysing maximal inspiratory and expiratory
pressure/forces. In the present study, for the first time, we have evaluated and related
RMs with endurance directly by analysing US measurements (shear modulus, thickness,
excursion, and velocity). An indirect method of assessing respiratory function is the result
of many factors (including airway obstruction, respiratory compliance, and RM strength)
that do not allow direct analysis of the RMs (Pałac & Linek, 2022). This may mean that the
improvement in endurance in athletes is a more complex phenomenon unrelated to an
exclusive change in RM morphology.
It is particularly surprising that there was no correlation between DA excursion and
aerobic endurance in the present study. DA excursion is related to exercise capacity
(Shiraishi et al., 2020) and can predict the improvement in exercise tolerance (Shiraishi
et al., 2020) in patients (especially with problems related to the respiratory system). DA
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excursion is related to pulmonary parameters like FVC, FEV1, and MIP, whereas DA
velocity is related to FVC, MIP, and MEP (Pałac & Linek, 2022). All of these spirometry
parameters are related to RM strength (Pałac & Linek, 2022). Thus, it was expected that
greater DA excursion would predispose to better endurance in examined football players.
Possibly in healthy people (and athletes who achieve higher performance in endurance
tests than the non-athlete population), the DA excursion is not as important in order
to improve endurance. An alternative explanation of the lack of correlation between DA
excursion and aerobic endurance may be the relatively similar endurance (training) level
of the footballers studied. However, there is a lack of scientific studies determining the
significance of DA excursion in athletes. Hence, the present study results are difficult to
interpret definitively.
Limitations
Due to the small sample size, this study is of a preliminary nature. The study group consisted
exclusively of football players from one team and age group, which may explain the high
homogeneity of the participants’ motor skills and US parameters. This, in turn, may have
influenced the narrow dispersion of the variables and, ultimately, the correlation values.
The results should not therefore be generalised to other sports. The participants were
included in the analysis regardless of their position; studies have shown that footballers’
profiles can vary according to where they play on the pitch (Oliva-Lozano et al., 2020).
US examinations were performed only in the supine position. Another limitation was the
collection of US measurements only during tidal breathing (except for excursion—maximal
inspiration and tidal expiration). It seems necessary to include US assessment of the RMs
during maximal respiratory efforts in future studies. For the purposes of this study, the
athletes’ endurance was indirectly determined. The MSRF is used as a test of aerobic
capacity (Voss & Sandercock, 2009). The beep test can be used as a health indicator in
children and adolescents (Mayorga-Vega et al., 2016), but it is a field test. Thus, the result
should not be interpreted as a direct measurement of cardiorespiratory fitness, only as an
estimation (Mayorga-Vega et al., 2016).
Strength and implications
To date, RMs have never been directly investigated in the context of their association with
athletes’ performance. Although this is a pilot study, we have shown for the first time
that some US parameters of the RMs may be related with motor skills (like speed in our
study). From this perspective, we have confirmed that such exploration is justified. US
provides an inexpensive and non-invasive tool for assessing RMs on wide populations. The
methodology used in this report to assess RMs is easy accessible and reliable. Thus, it seems
that the US of RMs in elite athletes is warranted in order to provide deeper insights into
the role of RMs in the context of different motor abilities. Previous studies have confirmed
the relationship between athletic performance and US parameters of lower-limb muscles
(Sarto et al., 2021). It is also worth noting that RMs (mainly DA) function itself is related to
pain sensation, stability, and balance. All these aspects are important in high-performance
sport.
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CONCLUSIONS
Shear modulus of the RMs, DA excursion, and velocity are related to speed score in
adolescent football players. In the examined population, endurance parameters were not
related to any US parameters of RMs. The current state of knowledge does not allow us
to conclusively determine how important US parameters of RMs can be in predicting
performance parameters (for example endurance and speed) in young athletes. However,
the results of the present study point to the need for further research into the role of US
measurements of RMs in the development of motor skills.
ADDITIONAL INFORMATION AND DECLARATIONS
Funding
The study was fully funded by the Team of Biomedical Basis of Physiotherapy, The Jerzy
Kukuczka Academy of Physical Education in Katowice. The funders had no role in study
design, data collection and analysis, decision to publish, or preparation of the manuscript.
Grant Disclosures
The following grant information was disclosed by the authors:
The Team of Biomedical Basis of Physiotherapy, The Jerzy Kukuczka Academy of Physical
Education in Katowice.
Competing Interests
The authors declare there are no competing interests.
Author Contributions
• Małgorzata Pałac conceived and designed the experiments, performed the experiments,
analyzed the data, prepared figures and/or tables, authored or reviewed drafts of the
article, and approved the final draft.
• Damian Sikora performed the experiments, prepared figures and/or tables, authored or
reviewed drafts of the article, and approved the final draft.
• Tomasz Wolny performed the experiments, authored or reviewed drafts of the article,
and approved the final draft.
• Paweł Linek conceived and designed the experiments, performed the experiments,
analyzed the data, prepared figures and/or tables, authored or reviewed drafts of the
article, and approved the final draft.
Human Ethics
The following information was supplied relating to ethical approvals (i.e., approving body
and any reference numbers):
The study was approved by the Ethics Committee at the Jerzy Kukuczka Academy of
Physical Education in Katowice
Data Availability
The following information was supplied regarding data availability:
The raw data is available in the Supplementary File.
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Supplemental Information
Supplemental information for this article can be found online at http://dx.doi.org/10.7717/
peerj.15214#supplemental-information.
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Relationship between respiratory muscles ultrasound parameters and running tests performance in adolescent football players. A pilot study.
Pałac, Małgorzata,Sikora, Damian,Wolny, Tomasz,Linek, Paweł