RESEARCH ARTICLE
Ventilatory efficiency during constant-load
test at lactate threshold intensity: Endurance
versus resistance exercises
Lluis Albesa-Albiol1, Noemı´ Serra-Paya´1, Marı´a Ana Garnacho-Castaño1, Lluis Guirao
Cano1,2, Eulogio Pleguezuelos Cobo1,3, Jose´ Luis Mate´-Muñoz4, Manuel V. Garnacho-
CastañoID1*
1 GRI-AFIRS, School of Health Sciences, TecnoCampus-Pompeu Fabra University, Mataro´, Barcelona,
Spain, 2 Department of Rehabilitation, Hospital Asepeyo, Sant Cugat, Barcelona, Spain, 3 Department of
Physical and Rehabilitation Medicine, Hospital de Mataro´, Mataro´, Barcelona, Spain, 4 Department of
Physical Activity and Sports Science, Alfonso X El Sabio University, Villanueva de la Cañada, Madrid, Spain
* mgarnacho@escs.tecnocampus.cat
Abstract
There is a lack of evidence about the ventilatory efficiency in resistance exercises despite
the key role played in endurance exercises. This study aimed to compare the cardiorespira-
tory, metabolic responses and ventilatory efficiency between half-squat (HS) and cycle
ergometer exercises during a constant-load test at the lactate threshold (LT) intensity. Eigh-
teen healthy male participants were randomly assigned in a crossover design to carry out
HS or cycle ergometer tests. For the three HS tests, a one repetition maximum (1RM) test
was performed first to determine the load (kg) corresponding to the 1RM percentages. In
the second test, the incremental HS exercise was carried out to establish the load (kg) at the
LT intensity. Finally, a constant-load HS test was performed at the LT intensity. The first
cycle ergometer test was incremental loading to determine the intensity in watts correspond-
ing to the LT, followed by a constant-load test at the LT intensity. A recovery time of 48
hours between each test was established. During both constant-load test, cardiorespiratory
and metabolic responses were monitored. A significant exercise mode x time interaction
effect was only detected in oxygen uptake (VO2), heart rate, and blood lactate (p < 0.001).
No differences were found between the two types of exercise in ventilatory efficiency (p
>0.05). Ventilation (VE) and carbon dioxide were highly correlated (p <0.001) in the cycle
ergometer (r = 0.892) and HS (r = 0.915) exercises. In the VO2 efficiency slope (OUES),
similarly significant and high correlations (p <0.001) were found between VO2 and log10 VE
in the cycle ergometer (r = 0.875) and in the HS (r = 0.853) exercise. Although the cardioven-
tilatory responses were greater in the cycle ergometer test as compared to HS exercise,
ventilatory efficiency was very similar between the two exercise modalities in a predomi-
nantly aerobic metabolism.
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OPEN ACCESS
Citation: Albesa-Albiol L, Serra-Paya´ N, Garnacho-
Castaño MA, Guirao Cano L, Pleguezuelos Cobo E,
Mate´-Muñoz JL, et al. (2019) Ventilatory efficiency
during constant-load test at lactate threshold
intensity: Endurance versus resistance exercises.
PLoS ONE 14(5): e0216824. https://doi.org/
10.1371/journal.pone.0216824
Editor: Daniel Boullosa, James Cook University
College of Healthcare Sciences, BRAZIL
Received: January 18, 2019
Accepted: April 29, 2019
Published: May 21, 2019
Copyright: © 2019 Albesa-Albiol et al. This is an
open access article distributed under the terms of
the Creative Commons Attribution License, which
permits unrestricted use, distribution, and
reproduction in any medium, provided the original
author and source are credited.
Data Availability Statement: All relevant data are
within the manuscript and its Supporting
Information files.
Funding: The author(s) received no specific
funding for this work.
Competing interests: The authors have declared
that no competing interests exist.
Introduction
Recent studies have used the lactate threshold (LT) or the ventilatory threshold as parameters
to monitor and assess cardiorespiratory responses [1, 2, 3], slow component of oxygen uptake,
and gross mechanical efficiency [4] in unusual resistance exercises using a cardiopulmonary
exercise tests (CPET), as also occurs in endurance exercise [5–9]. During constant-load test at
a load intensity equivalent to the LT, it was observed a greater cardiorespiratory response to
cycle ergometer exercise compared to the half-squat (HS). The cardiorespiratory and meta-
bolic response was stable in both types of exercise; greater muscular fatigue was observed after
completion of the HS test [2]. As could be expected, resistance exercises increased local muscu-
lar fatigue in the lower limbs, while endurance exercises increased cardiorespiratory response.
Cardiorespiratory fitness is frequently evaluated by means of ventilatory efficiency [10, 11].
The fundamental cause of ventilatory efficiency is the matching of ventilation (VE) and perfu-
sion in the lungs. The mismatching of perfusion and VE diminishes the efficiency of lung gas
exchange, demanding an increase in VE for a given CO2 output and arterial PCO2. This mis-
matching phenomenon contributes essentially to hyperpnea and dyspnea [12] affecting venti-
latory performance. It is common to assess ventilatory efficiency in endurance exercises
mostly in different types of diseases or pathologies [13–14], in sports performance [11], and in
healthy subjects [10, 15], establishing the slope of the linear relationship between VE and car-
bon dioxide (VE/VCO2 slope) during an incremental test up to the anaerobic [16] or ventila-
tory threshold [17] and the ventilatory compensation point [10]. Another option to quantify
ventilatory efficiency in endurance exercises is to determine the oxygen uptake efficiency slope
(OUES). The OUES indicates how effectively oxygen is extracted and taken into the body dur-
ing incremental exercise [17]. The OUES is considered a very appropriate tool in the evalua-
tion of cardiovascular fitness in overweight adolescents [18], the severity of heart disease [19],
the effects of physical training or treatment [20, 21], and the risk of a serious or fatal event
[22].
Although many studies have analyzed the slope of VE/VCO2 and OUES by age, sex, fitness
level, and diseases in endurance exercises [10, 11, 14, 17, 19], it is unusual to observe studies
comparing VE/VCO2 slope and OUES between different exercise modalities [23, 24]. Sun
et al. [10] demonstrated that VE/VCO2 slope is not exercise mode-dependent, however, Davis
et al. detected that VE/VCO2 slope was lower on the cycle ergometer than the treadmill in
women but not in men [25]. For OUES, treadmill values were higher than cycle ergometer
[24]. Recently, Salazar-Martinez et al. demonstrated that ventilatory efficiency was unaffected
by ergometer type [26]. The assumption that ventilatory efficiency could be similar between
different exercise modalities is controversial and more research is needed to compare several
exercise modes. Despite the importance that has been given in the scientific literature to the
assessment of ventilatory efficiency in endurance exercises in healthy people and especially in
the clinical settings, it is a field of knowledge that needs to be explored in resistance exercises.
There are no previous data regarding VE/VCO2 slope and OUES in HS exercise and, to the
best of our knowledge, ventilatory efficiency has not been compared between resistance and
endurance exercises.
In cardiorespiratory fitness assessment, this knowledge could have an added value in select-
ing the type of exercise to improve ventilation efficiency. If resistance exercises demonstrate
adequate ventilatory efficiency, professionals in the health field could use resistance training to
increase local muscle endurance while maintaining good ventilatory efficiency.
It is common to assess ventilatory efficiency during incremental endurance tests, however,
prolonged constant-load endurance tests can be recommended as a good option in the clinical
health setting to determine the VE/VCO2 slope [27, 28] or OUES because they do not subject
Ventilatory efficiency in resistance exercises at lactate threshold intensity
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the participants to significant cardiorespiratory, metabolic, and muscular stress. A constant-
load test at LT intensity might be an interesting alternative for applying to healthy people in
both endurance and resistance exercises to assess ventilatory efficiency without inducing a
strenuous cardiorespiratory and metabolic stress.
The main objective of this study was to compare the ventilatory efficiency, measured by
OUES and VE/VCO2 slope, and cardioventilatory responses of HS and cycle ergometer exer-
cise in a constant-load test at LT intensity. A secondary goal was to determine the relationship
between the OUES and the VE/VCO2 slope in both exercise modalities in each participant.
Material and methods
Participants
Eighteen healthy male participants were recruited among the students of the Department of
Physical Activity and Sports Sciences (age: 21.8 ± 1.5 years, height: 180.3 ± 5.7 cm, weight:
82.6 ± 9.0 kg, body mass index: 25.4 ± 2.0). All participants had at least 6 months of resistance
training experience and were completely familiar with the HS exercise and the cycle ergometer.
Four exclusion criteria were established: 1) any cardiovascular, metabolic, neurological,
pulmonary, or orthopedic disorder that could limit exercise performance, 2) the use of any
medication, supplements, or substance that could improve performance, 3) 1RM 150 kg in
the exercise of the HS, 4) elite athlete status.
Eligible participants were informed of the tests to be performed and those who agreed with
the study protocols signed their written consent to participate. The subjects were instructed to
abstain from other exercise or training during the two-week study period. The study protocol
adhered to the principles of the Declaration of Helsinki for studies with human beings and was
approved by the Ethics Committee of the Alfonso X El Sabio University (Villanueva de la
Cañada, Madrid, Spain).
Experimental design
The participants visited the Exercise Physiology Laboratory five times during the two-week
study period, at the same time of day (± 2 hours) and in similar environmental conditions
(room temperature 21–25˚C, atmospheric pressure 715–730 mm Hg, relative humidity ~
45%). Participants were randomly assigned in a crossover design to perform HS or cycle
ergometer tests. A rest period of 48 hours was established between each of the five tests. The
protocols were implemented according to procedures previously established by our research
group [2].
For the three HS tests, a one repetition maximum (1RM) test was performed first to deter-
mine the load (kg) corresponding to the 1RM percentages to be used during the second test,
the incremental HS exercise to establish the load (kg) at the intensity corresponding to the LT.
Finally, a constant-load HS test was performed at the LT intensity established during the incre-
mental exercise test. The first cycle ergometer test was incremental loading to determine the
intensity in watts (W) corresponding to the LT, followed by a constant load test at the LT
intensity. During both constant-load test, acute cardiorespiratory and metabolic responses
were monitored. The timing of the blood lactate sampling was the same for both the HS and
cycle ergometer testing.
Half squat tests
In the HS tests, a Smith machine (Matrix Fitness, Johnson Health Tech, Cottage Grove, MN,
USA) was used to ensure safe and controlled movements. HS technique was determined as in
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previous studies [3, 29]. The variation in range of motion (ROM) during HS exercise was accu-
rately determined during a familiarization session and in all the tests. Participants positioned
themselves under the barbell in an upright position with the knees and hips fully extended and
legs spread approximately at the shoulders’ width. The barbell was placed on the upper back
(trapezius muscle), approximately at the level of the acromion. During the descent of the bar,
participants flexed the knees and hips (eccentric action) to lower the barbell in a controlled
manner, until 900 flexion of the knees [30]. From this position, the concentric muscle action
was started until fully extending the knees and hips. The body position was individually
adjusted and exactly replicated on each HS test.
Each HS test started with a 5-minute low-intensity general run and 5-minute general joint
mobility warm-up, followed by a specific warm-up of a series of 3–5 repetitions (HS) at a rela-
tive intensity of 40–60% of 1RM.
1RM test. After a 2-minute rest, the HS test protocols began. To determine 1RM, 3–5
series were carried out, using an increasing weight each time. The 1RM was defined as the last
load lifted by the subject, completing a knee extension to the required position. The rest period
between each attempt was 4 minutes.
Incremental HS test. The incremental HS test was carried out in 6 one-minute series, at
relative intensities of 10%, 20%, 25%, 30%, 35%, and 40% 1RM as described in previous studies
[2, 4, 29]. In each series, 30 repetitions of 2 seconds each were performed (1 second for eccen-
tric muscle action and 1 second for concentric action), using a metronome to establish the
rhythm; a member of the research team provided visual and verbal cues to maintain an ade-
quate rate. A passive rest period of 2 minutes between series was established. During this
period, blood samples were collected by an experienced researcher and the corresponding load
was increased. The test ended when the repetitions were no longer executed correctly or was
voluntarily terminated by the participant when he could not perform the repetitions at the
established cadence. Blood samples (5 μL) were obtained by pricking the finger 30 seconds
after the end of each series. Lactate levels were measured using a portable analyzer (Lactate Pro
LT-1710, Arkray Factory Inc., KDK Corporation, Siga, Japan).
Based on the algorithmic adjustment method described by Orr et al. [31], LT was defined as
the load intensity at which blood lactate concentrations begin to increase exponentially [32].
LT was detected by two-segment linear regression, placing the 2 emergent linear regression
equations for each segment at the point of intersection between a plot of blood lactate concen-
tration and relative intensity [33]. Data analysis was done using Matlab version 7.4 (Math-
Works, Natick, MA, USA).
Constant-load HS test. In the constant load HS test, 21 sets of 15 repetitions were per-
formed. The duration of each set was 30 seconds (1 second each for the eccentric and concen-
tric phases, guided by a metronome and visual and verbal signals), with 1-minute rest between
sets. The entire constant-load test lasted 31 minutes. Respiratory exchange data were recorded
during the constant-load test using a breath-by-breath open-loop gas analyzer (Vmax spectra
29, Sensormedics Corp., Yorba Linda, California, USA), previously calibrated. VO2, VE,
VCO2, and respiratory exchange ratio (RER) were monitored. The heart rate was quantified
every 5 seconds by telemetry (RS-800CX, Polar Electro OY, Finland). To determine lactate
concentrations, finger-prick blood samples were obtained, as described for the incremental
test, at rest and 30 seconds after the end of 7 HS sets (S): S3, S6, S9, S12, S15, S18 and S21.
Cycle ergometer tests
The incremental and constant-load tests on a cycle ergometer (Monark ergomedic 828E,
Vansbro, Sweden) included a 5-minute warm-up at a pedaling rate of 50 rev.min-1 and a load
Ventilatory efficiency in resistance exercises at lactate threshold intensity
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of 50 W, followed by 5 minutes of dynamic joint mobility and stretching exercises. The load
during the incremental and constant-load tests was defined according to the characteristics of
the cycle ergometer, as previously described [34]. Briefly, pedaling at an intensity of 50 W is
the same as pedaling at a rate of 50 rev.min-1 at a load of 1-kilogram force (kgf). To increase
the load by 25 W during an incremental protocol, pedaling cadence at a rate of 50 rev.min-1
should be performed at a load equivalent to 0.5 kfg. After 2 minutes of rest, the specific tests on
the cycle ergometer began.
Incremental cycle ergometer test.
The incremental test using a ramp protocol that
started with a load of 50 W (50 rev.min-1 at a load of 1kgf), increased in steps of 25 W.min-1
until completion of 8 min at a pedaling rate of 50 rev.min-1 at a load of 0.5 kgf. Blood samples
(5 μL) were obtained by finger pricking at rest and every 2 minutes during the incremental
test. The LT was detected by inspecting the plot of blood lactate concentrations against the
workload, according to the protocol described by Weltman et al. [35]. LT was defined as the
highest exercise load completed when an increase of 0.5 mmol.L-1 was detected over baseline
concentrations in at least 2 consecutive samples.
Constant-load cycle ergometer test.
The constant load cycle ergometer test was per-
formed with continuous pedaling at a rate between 70–80 rev.min-1 at an intensity (W) equiva-
lent to the LT, previously determined in the incremental test. The load in kfg was individually
adjusted to each subject at 70–80 rev.min-1 to develop the W corresponding to the LT inten-
sity. Total duration of the test was 31 minutes. The blood lactate samples were obtained with
the same portable analyzer as in the HS test, at the beginning of the test and (coinciding with
the timing in the HS test) at the following minutes (M) thereafter: M4, M8.5, M13, M17.5,
M22, M26.5, M31. During the constant-load test, respiratory exchange and heart rate data
were recorded as described in the HS constant-load test.
Ventilatory efficiency
The ventilatory efficiency of each participant was determined in two ways: 1) the slope of the
relationship between VE and VCO2 during each constant-load test; 2) the OUES slope, calcu-
lated as the relationship between VO2 and the logarithm of the VE during the constant-load
test: VO2 = a log10 VE + b).
Statistical analysis
The Shapiro-Wilk test was used to verify the normal distribution of the data, reported as
mean, standard deviation (SD), and confidence intervals (95% CI). To identify significant dif-
ferences between the HS and cycle ergometer exercises in the cardioventilatory and lactate var-
iables, a general linear model was performed with a two-way analysis of variance (ANOVA)
for repeated measurements. The two factors were the exercise mode (HS or cycle ergometer)
and time point (corresponding to 7 control points in both exercise modes). When appropriate,
a post-hoc Bonferroni adjustment was implemented for multiple comparisons. To determine
the differences between the two exercise modes in the VE/VCO2 and OUES slopes, Student-t
was applied for related samples. The slope of VE/VCO2 and OUES was calculated by linear
regression between VE and VCO2 and between VO2 and log10 VE, respectively. The Pearson
product-moment correlation coefficients were calculated to determine significant relation-
ships between the VE and the VCO2 and between the VO2 and the log10 VE, and to establish
the possible relationship between the OUES and the VE/VCO2 slope.
Partial eta square (ηp
2) was calculated to determine the magnitude of the response in
ANOVA analysis. Cohen´s d for the planned comparisons was used to determine effect sizes.
A large effect size was defined as ηp
2  0.26, d  0.80; moderate ηp
2  0.13, d  0.40; and
Ventilatory efficiency in resistance exercises at lactate threshold intensity
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small ηp
2 < 0.02, d < 0.40 [36]. Statistical power (SP) was also determined. The intraclass cor-
relation coefficients and the percentage of variation coefficients were calculated to determine
the relative and absolute reliability. The level of significance was set at p <0.05. All statistical
methods were performed using the SPSS Statistics software package version 23.0 for Macintosh
(SPSS, Chicago, IL, USA). The graphics were made in the Microsoft Excel version 16.20 for
Mac.
Results
Anthropometric characteristics and incremental test data for the HS and cycle ergometer exer-
cises are shown in Table 1.
Differences in cardioventilatory and lactate responses are shown in Table 2. The mean of
the intraclass correlation coefficients and the coefficients of variation for cardioventilatory var-
iables and lactate were 0.970 (0.942–0.987) and 6.7% ± 3.4%, respectively.
For absolute VO2, a significant exercise mode x time interaction effect was observed
(p = 0.007, F(6, 102) = 3.18). Bonferroni test confirmed that VO2 was significantly higher in
cycle ergometer than HS exercise at the 7 established control points (p <0.001; large effect
d  1.64). In cycle ergometer, a significant lower VO2 was detected in M4 regarding the rest of
the control points (p  0.002; moderate effect d  0.46 and  0.60). However, a VO2 stabiliza-
tion was observed after M8.5 (p > 0.05). In HS exercise, a significant increase in VO2 was
observed (p < 0.05) in S3 with respect to S6 (moderate effect, d = 0.46), S18 (large effect, d =
0.95), and S21 (large effect, d = 0.86) (Fig 1A).
No significant exercise mode x time interaction effect was found for the relative VO2
(p > 0.05) and VE variable (p > 0.05).
For heart rate, a significant effect (p <0.001) was observed for exercise mode x time interac-
tion (F(6, 102) = 5.85). The Bonferroni test determined that heart rate was significantly lower in
HS exercise than in cycle ergometer test at the 7 established control points (p <0.05; in M4/S3,
moderate effect d = 0.49; rest of control points large effect d  0.94). In cycle ergometer exer-
cise, a significant increase in heart rate was confirmed in M4 regarding all control points
(p < 0.01; moderate effect versus M8.5 and M13, d  0.62 and  0.74; large effect versus
M17.5, M22, M26.5, M31, d  0.83) (Fig 1B).
Blood lactate concentrations indicated a significant exercise mode x time interaction
(p < 0.001, F(7, 119) = 6.93). The Bonferroni adjustments showed a significant increase from
rest period in both exercise modes (p 0.005; large effect d  1.71). Significant higher blood
Table 1. Descriptive data related to anthropometric characteristics, 1RM- and incremental-load tests.
Variables
Mean (SD)
Participants
N = 18
Age (years)
21.2 (1.5)
Height (cm)
180.3 (5.7)
Weight (kg)
82.6 (9.0)
BMI (kg.m-2)
25.4 (2.1)
1RM in HS (kg)
206.3 (36.4)
HS load at LT (kg)
51.2 (9.0)
HS relative intensity at LT (%)
25.8 (4.6)
CYC load at LT (W)
130.8 (24.8)
Abbreviations: 1RM = one-repetition maximum; BMI: body mass index; CYC: cycle-ergometer; HS = half-squat;
LT = lactate threshold; SD = standard deviation.
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lactate levels were found in HS exercise regarding cycle ergometer (p <0.05) at control points
M22/S15 (moderate effect, d = 0.72), M26.5/S18 (large effect, d = 0.82), and M31/S21 (large
effect, d = 1.19) (Fig 2).
In the RER, no significant interaction effect was observed for exercise mode x time
(p > 0.05).
Regarding VE/VCO2 slope and OUES, no differences were found between the two types of
exercise (p >0.05) (Fig 3).
In the VE/VCO2 slope, VE and VCO2 were highly correlated (p <0.001), both in the cycle
ergometer (r = 0.892) and HS (r = 0.915) modalities (Fig 4A and 4B, respectively).
In the OUES, similarly high correlations (p <0.001) were found between VO2 and log10 VE
in the cycle ergometer (r = 0.875) and in the HS (r = 0.853) (Fig 5A and 5B, respectively).
No significant correlation was found between the OUES and the slope of the VE/VCO2 in
the HS (r = -0.345, p = 0.160) nor in the cycle ergometer (r = 0.315, p = 0.203). Also, no signifi-
cant correlation was observed between the HS and cycle ergometer modes in OUES (r = 0.356,
p = 0.147) or VE/VCO2 slope (r = 0.422, p = 0.081).
Discussion
To the best of our knowledge, this study applied two novelties in methodological approach,
with respect to previous research. First, it determined ventilatory efficiency in HS exercise by
two distinct methods (VE/VCO2 slope and OUES); second, it compared HS and cycle ergome-
ter ventilatory efficiency in constant-load tests conducted at an intensity equivalent to the LT.
Although the cardioventilatory responses were greater in the cycle ergometer test as compared
to HS, ventilatory efficiency was very similar between the two exercise modalities. In addition,
the blood lactate concentrations were similar between both exercise modes although these val-
ues were slightly higher in HS exercise than in the cycle ergometer exercise at the end of the
constant-load tests.
Table 2. Differences in cardioventilatory and lactate responses between half-squat vs cycle-ergometer during constant-load test at lactate threshold intensity.
CYC
(95% CI)
HS
(95% CI)
P1
ES/SP
P2
ES/SP
P3
ES/SP
VO2 (L.min-1)
2.2
1.6
0.007
< 0.001
< 0.001
(2.0–2.5)
(1.5–1.7)
0.2/0.9
0.6/1.0
0.6/1.0
VO2 (mL.kg-1.min-1)
19.8
27.8
0.517
< 0.001
< 0.001
(18.6–20.9)
(24.8–30.8)
(0.1–0.3)
(0.2–1.0)
(0.6–1.0)
VCO2 (L.min-1)
2.1
1.5
0.062
< 0.001
< 0.001
(1.8–2.3)
(1.4–1.6)
0.1/0.7
0.6/1.0
0.6/1.0
VE (L.min-1)
53.7
43.1
0.510
< 0.001
0.002
(48.2–59.2)
(40.1–46.1)
0.1/0.3
0.4/1.0
0.5/0.9
RER
0.9
0.9
0.923
< 0.001
0.084
(0.9–0.9)
(0.9–1.0)
0.0/0.1
0.5/1.0
0.2/0.4
HR (beat.min-1)
139.6
123.8
< 0.001
< 0.001
< 0.001
(131.2–148.0)
(116.7–130.8)
0.3/1.0
0.6/1.0
0.6/1.0
Lactate (mmol.L-1)
2.6
2.8
< 0.001
< 0.001
0.148
(2.2–2.9)
(2.6–3.1)
0.3/1.0
0.8/1.0
0.1/0.3
Abbreviations used: CYC: cycle-ergometer; ES: effect size; HR: heart rate; HS: half-squat; L: liter; min: minute; RER: respiratory exchange ratio; SP: statistical power;
VCO2: carbon dioxide production; VE: minute ventilation; VO2: oxygen uptake. P1 Significant differences for exercise mode x time interaction effect. P2 Significant
differences for time effect. P3 Significant differences for exercise mode effect. Data are provided as mean and 95% confidence intervals (95% CI).
https://doi.org/10.1371/journal.pone.0216824.t002
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These findings replicated the results obtained in previous investigations, in which the
cardiorespiratory responses were higher in the cycle ergometer test than in HS exercise [2].
The constant-load HS test at LT intensity likely induced a lower cardioventilatory response
because a rest time was implemented between sets. To date, it has been unfeasible to perform a
continuous protocol in the HS exercise at the LT intensity. In theory, a continuous HS proto-
col would increase intramuscular pressure leading to augmented muscle tension and progres-
sive fatigue. These physiological mechanisms would produce the collapse of capillaries and
diminish the oxygen available into the muscle and thus increasing the blood lactate levels [37].
Although it is usual to find a different cardiorespiratory response between several endurance
exercise modalities at the same relative intensity [38], the available studies comparing resis-
tance versus endurance exercises during constant-load test at LT intensity are currently insuf-
ficient to draw more precise conclusions.
The VE/VCO2 slope and OUES results obtained in both exercises are considered normal
and comparable to other studies with healthy adults (19–30 in VE/VCO2 slope, 2.55 ± 1.01
n = 417 in OUES) [10, 16, 24]. In elite youth cyclists [11], the slope of the VE/VCO2 was simi-
lar (about 28) to our study, but the OUES was higher: 3.8 vs. 2.5 in our study. The difference
could be due to the novel methodology used in our study and the greater cardiorespiratory fit-
ness of elite youth cyclists. No studies are available for comparison of the VE/VCO2 slope,
cycle ergometer values, or HS data in a constant-load test at LT intensity. However, our results
on ventilatory efficiency were very similar to those obtained in other studies in endurance
exercises (cycling) at the intensity of the anaerobic threshold [11], perhaps because both
Fig 1. Multiple comparisons between cycle ergometer (CYC) and half-squat (HS): (A) Oxygen uptake (VO2). (B) Heart rate (HR). δ Significant differences
p < 0.05 between cycle ergometer and half-squat at each checkpoint. † Significantly different from M8.5, M13, M17.5, M22, M26.5, M31 in cycle ergometer,
p < 0.01. ⍵ Significantly different from M8.5, M17.5 in cycle ergometer, p = 0.017. ⏚ Significantly different from S6, S18, S21 in HS exercise, p < 0.05. ⏆
Significantly different from S21 in HS exercise, p = 0.026.
https://doi.org/10.1371/journal.pone.0216824.g001
Fig 2. Multiple comparisons between cycle ergometer (CYC) and half-squat (HS) in blood lactate. ⏚ Significantly different from S3, S6, S9, S12, S15, S18,
S21 in HS exercise, p < 0.001. † Significantly different from M4, M8.5, M13, M17.5, M22, M26.5, M31 in cycle ergometer, p < 0.01. δ Significantly different
from cycle ergometer in M22/S15, M26.5/S18, M31/S21, p < 0.05. ⍵ Significantly different from M4 in cycle ergometer, p = 0.028. ⏆ Significantly different
from S3 and S6 in HS exercise, p < 0.05.
https://doi.org/10.1371/journal.pone.0216824.g002
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Fig 3. Differences between cycle ergometer (CYC) and half-squat (HS) in the VE/VCO2 slope and OUES. No significant differences between both
exercise modalities.
https://doi.org/10.1371/journal.pone.0216824.g003
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Fig 4. Linear relationship between ventilation (VE) and carbon dioxide (VE/VCO2 slope): (A) Cycle ergometer (CYC). (B) Half-squat (HS).
https://doi.org/10.1371/journal.pone.0216824.g004
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Fig 5. Relationship between oxygen uptake (VO2) and log10 VE (OUES): (A) Cycle ergometer (CYC). (B) Half-squat (HS).
https://doi.org/10.1371/journal.pone.0216824.g005
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intensities (LT and anaerobic thresholds) reflect a similar metabolic moment, beyond which
lactate concentrations begin to increase. Our data from both exercise modes in healthy young
adults verify that this protocol could be another option to evaluate the slope of VE/VCO2 and
OUES in a mostly aerobic metabolism, controlling the acidosis of the body, without having to
reach the high intensities and avoiding a higher cardiorespiratory stress that could become
problematic in some pathologies. Probably, during a constant-load test at moderate intensity
(LT) the relationship between VE and both VCO2 and VO2 is normally stable and uniform
before the onset of ventilatory compensation for the exercise-induced lactic acidosis [10], justi-
fying, at least in part, the similarities detected in VE/VCO2 slope and OUES between both
exercise modalities at the same metabolic state.
A surprising aspect of this study was the almost identical values in the ventilatory efficiency
observed in the HS and cycle ergometer tests. Studies comparing the VE/VCO2 slope and the
OUES in different types of exercises are rare; therefore, there is a significant lack of informa-
tion about which exercise modality could induce a higher ventilatory efficiency. Our findings
show that two types of exercise with different cardioventilatory responses induce the same ven-
tilatory efficiency at similar metabolic intensity. During incremental exercise tests [23], no sig-
nificant changes were found between treadmill and cycle ergometer trials, although both
exercise modalities showed a lower VE/VCO2 slope (higher efficiency) compared to a robot-
ics-assisted tilt table. A study compared OUES in 17 healthy subjects in two exercise modali-
ties, observing higher values in the treadmill test compared to the cycle ergometer [24].
Although further evidence is needed, ventilatory efficiency could be dependent on the type of
exercise, test protocol, and mode of assessing ventilatory efficiency (OUES vs VE/VCO2
slope).
It was expected that subjects with a lower VE/VCO2 slope (greater efficiency) throughout
each of the tests would increase their OUES. The lack of significant correlation between the
OUES and the slope of the VE/VCO2 in the two exercise modalities analyzed indicates that
those subjects who showed greater ventilatory efficiency in the HS did not achieve greater ven-
tilatory efficiency in the cycle ergometer. The OUES has been accepted as a valid submaximal
measure of the function and prognosis of disease [39], and the slope of VE/VCO2 is a reliable
assessment in healthy adults [40] and in those with pathologies [41]. However, their usefulness
in healthy and athletically trained people is dubious. It is not yet clear which factors contribute
to modify ventilatory efficiency during exercise, but the established postulates through this dis-
cussion may be more relevant in the clinical field than in fitness and sports performance
because it seems that the VE/VCO2 slope did not change in elite cyclists after 16 weeks of train-
ing [11] and, regardless of gender, in children [42] and healthy adults [10] engaging in exer-
cise. Training did not improve the OUES in healthy subjects [43] and could have a limited
effect in athletes [11].
As a practical application, these findings could be an interesting alternative for the processes
of physical rehabilitation and recovery from diseases associated with a loss of strength and
muscle mass. For example, patients with heart failure are characterized by a significant loss of
muscle mass, and these same physiological mechanisms are closely related to dyspnea and ven-
tilatory fatigue [44]. Therefore, ventilatory efficiency is related to the severity of heart failure
with reduced ejection fraction [45, 46] and, as a corollary, poor ventilatory efficiency is related
to increased morbidity and mortality. In addition, it is common to diagnose strength and mus-
cle loss (sarcopenia) in older adults. Sarcopenia is a prevalent syndrome associated with pre-
mature mortality in elderly [47]. Resistance exercises at LT intensity could increase local
muscular endurance avoiding the losses of strength and muscular mass and, in addition, with
the same ventilatory efficiency that could produce the cycle ergometer exercise. Unfortunately,
our arguments cannot be consolidated with previous studies in different pathologies, as data
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clarifying the effect of the resistance exercises to LT intensity in patients with heart failure or
sarcopenia are not available; therefore, these observations remain purely intuitive and specula-
tive. It is clear that the combination of both resistance and endurance training has improved
exercise capacity and diastolic function in patients with heart failure with reduced ejection
fraction [48]. Accordingly, the combination of resistance exercises and endurance exercises
could be an adequate methodology to increase cardiorespiratory response (endurance exer-
cises) on the one hand and strength and muscular resistance (resistance exercises) on the other
hand.
There are some limitations in this study with regard to the HS exercise protocol, which
should be considered. The experimental procedures established in both incremental tests
prompt controversial debate with regards to the location of the LT. Consequently, the relative
intensity or external load prescribed in each exercise could have been different during both
constant-load tests. In this case, an important bias would occur when comparing ventilatory
efficiency, cardiorespiratory and metabolic responses between both exercises. However, the
results reported by our research group in a recent study [49] revealed that the detection of the
LT in both exercises using this same methodology could occur at a similar metabolic instant
and relative intensity according to the criteria defined by Binder et al. [50]. In both incremen-
tal tests, an equivalent load intensity was produced at the LT, however, cardiorespiratory
response was higher in cycle ergometer than in HS exercise during constant-load tests. It is
habitual to observe an unequal cardioventilatory response when several exercise modes are
compared at the same relative intensity or external load [51]. An identical trend was found in
other studies that compared blood lactate, RER and cardiorespiratory responses in various
exercises at lower and moderate intensities [38, 52]. Probably, cardiorespiratory responses are
exercise mode-dependent at the same metabolic intensity and, therefore, these differences
seem larger and more important to considerer at lighter and moderate intensities [38].
We cannot fail to mention that the recovery time established between each series is a key
factor in maintaining low and stable levels of blood lactate in a primarily aerobic metabolism.
It is assumed that this rest period would mainly affect the mechanisms of cardioventilatory
recovery. However, our research group has observed in preliminary trials (unpublished data)
that the combination of resistance exercises (in the form of circuit training), without rest
between exercises, could keep blood lactate concentrations low and stable. The results stated in
this study have important implications for our understanding of the load intensity and the
recovery time that regulate ventilatory efficiency in a predominantly aerobic metabolism in
HS exercise. Probably, a discontinuous constant-load HS test might induce a similar metabolic
intensity and ventilatory efficiency as occurred during continuous constant-load cycle ergom-
eter test. Further studies are needed to determine if the hypothetical increase in VO2 and venti-
lation associated with a continuous protocol without recovery time between series would
increase ventilatory efficiency in the resistance exercises to LT intensity.
Conclusions
Our findings showed that:
1. Cardioventilatory response was lower in HS exercise than in cycle ergometer during a con-
stant-load test at LT intensity.
2. Ventilatory efficiency was equally efficient in the HS resistance exercise and in cycle ergom-
eter exercise in a predominantly aerobic metabolism, which could have a significant impact
in healthy people.
Ventilatory efficiency in resistance exercises at lactate threshold intensity
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3. There was no correlation between the OUES and the slope of the VE/VCO2 in the two exer-
cise modalities analyzed. Those subjects who showed greater ventilatory efficiency in the
HS did not achieve higher ventilatory efficiency in the cycle ergometer.
4. Performing a constant-load HS protocol at LT intensity does not generate significant
cardiorespiratory stress, while ventilatory efficiency is maintained and muscle strength and
local muscular endurance, as well as gross mechanical efficiency, may improve according to
previous findings of our research group.
Further research is needed to analyze ventilatory efficiency for better understanding of ven-
tilatory mechanisms that conditioning resistance exercises performance in a predominantly
aerobic metabolism.
Supporting information
S1 File. Statistical analysis performed with the data obtained during constant-load test.
(DOC)
S1 Fig. Results for the preparation of the figures.
(XLSX)
Acknowledgments
We thank all our participants who volunteered to take part in this study.
Author Contributions
Conceptualization: Jose´ Luis Mate´-Muñoz, Manuel V. Garnacho-Castaño.
Data curation: Lluis Albesa-Albiol, Manuel V. Garnacho-Castaño.
Formal analysis: Jose´ Luis Mate´-Muñoz, Manuel V. Garnacho-Castaño.
Investigation: Lluis Albesa-Albiol, Noemı´ Serra-Paya´, Marı´a Ana Garnacho-Castaño, Lluis
Guirao Cano, Eulogio Pleguezuelos Cobo, Jose´ Luis Mate´-Muñoz, Manuel V. Garnacho-
Castaño.
Methodology: Lluis Albesa-Albiol, Noemı´ Serra-Paya´, Marı´a Ana Garnacho-Castaño, Lluis
Guirao Cano, Eulogio Pleguezuelos Cobo, Jose´ Luis Mate´-Muñoz, Manuel V. Garnacho-
Castaño.
Supervision: Lluis Albesa-Albiol, Noemı´ Serra-Paya´, Marı´a Ana Garnacho-Castaño, Lluis
Guirao Cano, Eulogio Pleguezuelos Cobo, Jose´ Luis Mate´-Muñoz, Manuel V. Garnacho-
Castaño.
Validation: Lluis Albesa-Albiol, Noemı´ Serra-Paya´, Marı´a Ana Garnacho-Castaño, Lluis
Guirao Cano, Eulogio Pleguezuelos Cobo, Jose´ Luis Mate´-Muñoz, Manuel V. Garnacho-
Castaño.
Visualization: Lluis Albesa-Albiol, Noemı´ Serra-Paya´, Marı´a Ana Garnacho-Castaño, Lluis
Guirao Cano, Eulogio Pleguezuelos Cobo, Jose´ Luis Mate´-Muñoz, Manuel V. Garnacho-
Castaño.
Writing – original draft: Lluis Albesa-Albiol, Jose´ Luis Mate´-Muñoz, Manuel V. Garnacho-
Castaño.
Ventilatory efficiency in resistance exercises at lactate threshold intensity
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Writing – review & editing: Lluis Albesa-Albiol, Noemı´ Serra-Paya´, Marı´a Ana Garnacho-
Castaño, Lluis Guirao Cano, Eulogio Pleguezuelos Cobo, Jose´ Luis Mate´-Muñoz, Manuel
V. Garnacho-Castaño.
References
1.
de Sousa NM, Magosso RF, Pereira GB, Souza MV, Vieira A, Marine DA, et al. Acute cardiorespiratory
and metabolic responses during resistance exercise in the lactate threshold intensity. Int J Sports Med.
2012; 33: 108–113. https://doi.org/10.1055/s-0031-1286315 PMID: 22127560
2.
Garnacho-Castaño MV, Domı´nguez R, Mate´-Muñoz JL. Understanding the meaning of lactate thresh-
old in resistance exercises. Int J Sports Med. 2015; 36: 1–7. https://doi.org/10.1055/s-0034-1384545
3.
Mate´-Muñoz JL, Domı´nguez R, Lougedo JH, Garnacho-Castaño MV. The lactate and ventilatory
thresholds in resistance training. Clin Physiol Funct Imaging. 2016: 1–7. https://doi.org/10.1111/cpf.
12327 PMID: 26749178
4.
Garnacho-Castaño MV, Albesa-Albiol L, Serra-Paya N, Gomis Bataller M, Pleguezuelos Cobo E,
Guirao Cano L, et al. Oxygen uptake slow component and the efficiency of resistance exercises. J
Strength Cond Res. 2018. https://doi.org/10.1519/JSC.0000000000002905 PMID: 30335719
5.
Bacon L, Kern M. Evaluating a test protocol for predicting maximum lactate steady state. J Sports Med
Phys Fitness. 1999; 39(4): 300–8. PMID: 10726430
6.
Coen B, Urhausen A, Kindermann W. Individual anaerobic threshold: methodological aspects of its
assessment in running. Int J Sports Med. 2001; 22: 8–16. https://doi.org/10.1055/s-2001-11332 PMID:
11258646
7.
MacIntosh BR, Esau S, Svedahl K. The lactate minimum test for cycling: estimation of the maximal lac-
tate steady state. Can J Appl Physiol. 2002; 27(3): 232–49. PMID: 12180316
8.
Ribeiro LFP, Balakian Jr P, Malachias P, Baldissera V. Stage length, spline function and lactate mini-
mum swimming speed. J Sports Med Phys Fitness. 2003; 43(3): 312–8. PMID: 14625512
9.
Garnacho-Castaño MV, Palau-Salvà G, Cuenca E, Muñoz-Gonza´lez A, Garcı´a-Ferna´ndez P, Del Car-
men Lozano-Estevan M et al. Effects of a single dose of beetroot juice on cycling time trial performance
at ventilatory thresholds intensity in male triathletes. 2018; 15(1):49. https://doi.org/10.1186/s12970-
018-0255-6 PMID: 30286760
10.
Sun XG, Hansen JE, Garatachea N, Storer TW, Wasserman K. Ventilatory efficiency during exercise in
healthy subjects. Am J Respir Crit Care Med. 2002; 166(11): 1443–1448. https://doi.org/10.1164/rccm.
2202033 PMID: 12450934
11.
Brown SJ, Raman A, Schlader Z, Stannard SR. Ventilatory efficiency in juvenile elite cyclists. J Sci Med
Sport. 2013; 16(3): 266–270. https://doi.org/10.1016/j.jsams.2012.06.010 PMID: 22840997
12.
Reindl I, Kleber FX. Exertional hyperpnea in patients with chronic heart failure is a reversible cause of
exercise intolerance. Basic Res Cardiol. 1996; 91: 37–43 PMID: 8896742
13.
Arena R, Myers J, Guazzi M. The clinical and research applications of aerobic capacity and ventilatory
efficiency in heart failure: An evidence-based review. Heart Fail Rev. 2008; 13(2): 245–269. https://doi.
org/10.1007/s10741-007-9067-5 PMID: 17987381
14.
Chlif M, Chaouachi A, Ahmaidi S. Effect of aerobic exercise training on ventilatory efficiency and respi-
ratory drive in obese subjects. Respir Care. 2017; 62(7): 936–946. https://doi.org/10.4187/respcare.
04923 PMID: 28442632
15.
Koch B, Scha¨per C, Ittermann T, Spielhagen T, Do¨rr M, Vo¨lzke H, et al. Reference values for cardiopul-
monary exercise testing in healthy volunteers: The SHIP study. Eur Respir J. 2009; 33(2): 389–397.
https://doi.org/10.1183/09031936.00074208 PMID: 18768575
16.
Brown SJ, Brown JA. Heart rate variability and ventilatory efficiency. Int J Sports Med. 2009; 30(7):
496–502. https://doi.org/10.1055/s-0028-1112146 PMID: 19301223
17.
Baba R, Nagashima M, Goto M, Nagano Y, Yokota M, Tauchi N, et al. Oxygen uptake efficiency slope:
a new index of cardiorespiratory functional reserve derived from the relationship between oxygen con-
sumption and minute ventilation during incremental exercise. J Am Coll Cardiol. 1996; 59: 55–62.
18.
Drinkard B, Roberts MD, Ranzenhofer LM, Han JC, Yanoff LB, Merke DP, et al. Oxygen uptake effi-
ciency slope as a determinant of fitness in overweight adolescents. Med Sci Sports Exerc. 2007; 39:
1811–1816. https://doi.org/10.1249/mss.0b013e31812e52b3 PMID: 17909409
19.
Arena R, Brubaker P, Moore B, Kitzman D. The oxygen uptake efficiency slope is reduced in older
patients with heart failure and a normal ejection fraction. Int J Cardiol. 2010; 144: 101–102. https://doi.
org/10.1016/j.ijcard.2008.12.143 PMID: 19174312
Ventilatory efficiency in resistance exercises at lactate threshold intensity
PLOS ONE | https://doi.org/10.1371/journal.pone.0216824
May 21, 2019
16 / 18
20.
Van Laethem C, Goethals M, Verstreken S, Walravens M, Wellens F, De Proft M, et al. Response of the
oxygen uptake efficiency slope to orthotopic heart transplantation: lack of correlation with changes in
central hemodynamic parameters and resting lung function. J Heart Lung Transplant. 2007; 26(9):
921–926. https://doi.org/10.1016/j.healun.2007.06.001 PMID: 17845931
21.
Van Laethem C, Van De Veire N, De Backer G, Bihija S, Seghers T, Cambier D, el al. Response of the
oxygen uptake efficiency slope to exercise training in patients with chronic heart failure. Eur J Heart
Fail. 2007; 9: 625–629. https://doi.org/10.1016/j.ejheart.2007.01.007 PMID: 17347033
22.
Myers J, Arena R, Dewey F, Bensimhon D, Abella J, Hsu L, et al. A cardiopulmonary exercise testing
score for predicting outcomes in patients with heart failure. Am Heart J. 2008; 156: 1177–1183. https://
doi.org/10.1016/j.ahj.2008.07.010 PMID: 19033016
23.
Saengsuwan J, Nef T, Laubacher M, Hunt KJ. Submaximal cardiopulmonary thresholds on a robotics-
assisted tilt table, a cycle and a treadmill: a comparative analysis. Biomed Eng Online. 2015; 14(1):
104. https://doi.org/10.1186/s12938-015-0099-0 PMID: 26555762
24.
Sun XG, Hansen JE, Stringer WW, Ward SA. Oxygen uptake efficiency plateau: Physiology and refer-
ence values. Eur J Appl Physiol. 2012; 112(3): 919–928. https://doi.org/10.1007/s00421-011-2030-0
PMID: 21695524
25.
Davis JA, Tyminski TA, Soriano AC, Dorado S, Costello KB, Sorrentino KM, Pham PH. Exercise test
mode dependency for ventilatory efficiency in women but not men. Clin Physiol Funct Imaging. 2006;
26(2): 72–78. https://doi.org/10.1111/j.1475-097X.2006.00657.x PMID: 16494595
26.
Salazar-Martı´nez E, de Matos TR, Arrans P, Santalla A, Orellana JN. Ventilatory efficiency response is
unaffected by fitness level, ergometer type, age or body mass index in male athletes. Biol Sport. 2018;
35(4): 393–398 https://doi.org/10.5114/biolsport.2018.78060 PMID: 30765925
27.
Hoshimoto-Iwamoto M, Koike A, Nagayama O, Tajima A, Uejima T, Adachi H, et al. Determination of
the VE/VCO2 slope from a constant work-rate exercise test in cardiac patients. J Physiol Sci. 2008; 58
(4): 291–295. https://doi.org/10.2170/physiolsci.RP006108 PMID: 18647443
28.
Form P, Reviewing P, Sheet C. Comparative determination of ventilatory efficiency from constant load
and incremental exercise testing. Cell Mol Biol Res. 1995; 41(3): 207–216.
29.
Garnacho-Castaño MV, Domı´nguez Herrera R, Ruiz Solano P, Mate´-Muñoz JL. Acute physiological
and mechanical responses during resistance exercise executed at the lactate threshold workload. J
Strength Cond Res. 2015; 29(10): 2867–2873. https://doi.org/10.1519/JSC.0000000000000956 PMID:
25844868
30.
Hartmann H, Wirth K, Klusemann M. Analysis of the load on the knee joint and vertebral column with
changes in squatting depth and weight load. Sports Med. 2013; 43(10): 993–1008. https://doi.org/10.
1007/s40279-013-0073-6 PMID: 23821469
31.
Orr GW, Green HJ, Hughson RL, Bennett GW. A computer linear regression model to determine venti-
latory anaerobic threshold. J Appl Physiol 1982; 52: 1349–1352 https://doi.org/10.1152/jappl.1982.52.
5.1349 PMID: 7096157
32.
Wasserman K, Mcllroy MB. Detecting the threshold of anaerobic metabolism in cardiac patients during
exercise. Am J Cardiol 1964; 14: 844–852 PMID: 14232808
33.
de Sousa NMF, Magosso RF, Pereira GB, Leite RD, Arakelian VM, Montagnolli AN, Andrade S, Baldis-
sera V. The measurement of lactate threshold in resistance exercise: a comparison of methods. Clin
Physiol Funct Imaging. 2011; 31(5): 376–381. https://doi.org/10.1111/j.1475-097X.2011.01027.x
PMID: 21771257
34.
Domı´nguez R, Garnacho-Castaño MV, Cuenca E, Garcı´a-Ferna´ndez P, Muñoz-Gonza´lez A, de Jesu´s
F, et al. Effects of Beetroot Juice Supplementation on a 30-s High-Intensity Inertial Cycle Ergometer
Test. Nutrients. 2017; 9(12):1360.
35.
Weltman A, Snead D, Stein P, Seip R, Schurrer R, Rutt R, et al. Reliability and validity of a continuous
incremental treadmill protocol for the determination of lactate threshold, fixed blood lactate concentra-
tions, and VO2max. Int J Sports Med. 1990; 11: 26–32. https://doi.org/10.1055/s-2007-1024757 PMID:
2318561
36.
Cohen J. A power primer. Psychol Bull. 1992; 112(1):155–9 PMID: 19565683
37.
Petrofsky JS, Phillips CA, Sawka MN, Hanpeter D, Stafford D. Blood flow and metabolism during iso-
metric contractions in cat skeletal muscle. J Appl Physiol 1981; 50: 493–502. https://doi.org/10.1152/
jappl.1981.50.3.493 PMID: 7251439
38.
Abrantes C, Sampaio J, Reis V, Sousa N, Duarte J. Physiological responses to treadmill and cycle exer-
cise. Int J Sports Med. 2012; 33: 26–30. https://doi.org/10.1055/s-0031-1285928 PMID: 22052028
39.
Akkerman M, van Brussel M, Hulzebos E, Vanhees L, Helders PJ, Takken T. The oxygen uptake effi-
ciency slope: what do we know?. J Cardiopulm Rehabil Prev. 2010; 30(6): 357–373. https://doi.org/10.
1097/HCR.0b013e3181ebf316 PMID: 20724931
Ventilatory efficiency in resistance exercises at lactate threshold intensity
PLOS ONE | https://doi.org/10.1371/journal.pone.0216824
May 21, 2019
17 / 18
40.
Davis JA, Sorrentino KM, Ninness EM, Pham PH, Dorado S, Costello KB. Test–retest reliability for two
indices of ventilatory efficiency measured during cardiopulmonary exercise testing in healthy men and
women. Clin Physiol Funct Imaging. 2006; 26(3): 191–196. https://doi.org/10.1111/j.1475-097X.2006.
00674.x PMID: 16640516
41.
Chua TP, Ponikowski P, Harrington D, Anker S, Webb-Peploe K, Clark AL, et al. Clinical correlates and
prognostic significance of the ventilatory response to exercise in chronic heart failure. J Am Coll Cardiol.
1997; 29: 1585–1590. PMID: 9180123
42.
Guerrero L, Naranjo J, Carranza MD. Influence of gender on ventilatory efficiency during exercise in
young children. J Sports Sci. 2008; 26: 1455–1457. https://doi.org/10.1080/02640410802255771
PMID: 18923953
43.
Mourot L, Perrey S, Tordi N, Rouillon JD. Evaluation of fitness level by the oxygen uptake efficiency
slope after a short-term intermittent endurance training. Int J Sports Med. 2004; 25(2): 85–91. https://
doi.org/10.1055/s-2004-819943 PMID: 14986189
44.
Keller-Ross ML, Johnson BD, Carter RE, Joyner MJ, Eisenach JH, Curry TB, et al. Improved ventilatory
efficiency with locomotor muscle afferent inhibition is strongly associated with leg composition in heart
failure. Int J Cardiol. 2016; 202: 159–166. https://doi.org/10.1016/j.ijcard.2015.08.212 PMID: 26397403
45.
Arena R, Myers J, Aslam SS, Varughese EB, Peberdy MA. Peak VO2 and VE/VCO2 slope in patients
with heart failure: a prognostic comparison. Am Heart J. 2004; 147: 354–60. https://doi.org/10.1016/j.
ahj.2003.07.014 PMID: 14760336
46.
Cohn JN, Rector TS. Prognosis of congestive heart failure and predictors of mortality. Am J Cardiol.
1988; 62: 25A–30A. PMID: 3389302
47.
Brown JC, Harhay MO, Harhay MN. Sarcopenia and mortality among a population-based sample of
community-dwelling older adults. J Cachexia Sarcopenia Muscle 2016; 7(3): 290–298. https://doi.org/
10.1002/jcsm.12073 PMID: 27239410
48.
Nolte K, Schwarz S, Gelbrich G, Mensching S, Siegmund F, Wachter R, et al. Effects of long-term
endurance and resistance training on diastolic function, exercise capacity, and quality of life in asymp-
tomatic diastolic dysfunction vs. heart failure with preserved ejection fraction. ESC heart failure. 2014;
1(1): 59–74. https://doi.org/10.1002/ehf2.12007 PMID: 28834666
49.
Garnacho-Castaño MV, Albesa-Albiol L, Serra-Paya´ N, Gomis Bataller M, Felı´u-Ruano R, Guirao Cano
L, Pleguezuelos Cobo E, Mate´-Muñoz JL. The slow component of oxygen uptake and efficiency in resis-
tance exercises: A comparison with endurance exercises. Front Physiol. 2019; 10: 357. https://doi.org/
10.3389/fphys.2019.00357 PMID: 31019469
50.
Binder RK, Wonisch M, Corra U, Cohen-Solal A, Vanhees L, Saner H, Schmid JP. Methodological
approach to the first and second lactate threshold in incremental cardiopulmonary exercise testing. Eur
J Cardiovasc Prev Rehabil. 2008; 15(6): 726–734. https://doi.org/10.1097/HJR.0b013e328304fed4
PMID: 19050438
51.
Orr JL, Williamson P, Anderson W, Ross R, McCafferty S, Fettes P. Cardiopulmonary exercise testing:
arm crank vs cycle ergometry. Anesth. 2013: 68(5): 497–501.
52.
Thomas TR, Ziogas G, Smith T, Zhang Q, Londeree BR. Physiological and perceived exertion
responses to six modes of submaximal exercise. Res Q Exerc Sport. 1995; 66: 239–246. https://doi.
org/10.1080/02701367.1995.10608838 PMID: 7481085
Ventilatory efficiency in resistance exercises at lactate threshold intensity
PLOS ONE | https://doi.org/10.1371/journal.pone.0216824
May 21, 2019
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Ventilatory efficiency during constant-load test at lactate threshold intensity: Endurance versus resistance exercises.
Albesa-Albiol, Lluis,Serra-Payá, Noemí,Garnacho-Castaño, María Ana,Guirao Cano, Lluis,Pleguezuelos Cobo, Eulogio,Maté-Muñoz, José Luis,Garnacho-Castaño, Manuel V