RESEARCH ARTICLE
Oxygen uptake kinetics and energy system’s
contribution around maximal lactate steady
state swimming intensity
Jailton Grego´rio Pelarigo1,2,3,4☯*, Leandro Machado3,4‡, Ricardo Jorge Fernandes3,4‡,
Camila Coelho Greco5‡, João Paulo Vilas-Boas3,4☯
1 University Catholic Center of Quixada´–UNICATO´ LICA, Quixada´, Ceara´, Brazil, 2 Metropolitan College of
Grande Fortaleza–FAMETRO, Fortaleza, Ceara´, Brazil, 3 Centre of Research, Education, Innovation and
Intervention in Sport, Faculty of Sport, University of Porto, Porto, Portugal, 4 Porto Biomechanics Laboratory,
LABIOMEP, University of Porto, Porto, Portugal, 5 Human Performance Laboratory, Physical Education
Department, São Paulo State University, Rio Claro, São Paulo, Brazil
☯ These authors contributed equally to this work.
‡ These authors also contributed equally to this work.
* jailtongp@hotmail.com
Abstract
The purpose of this study was to examine the oxygen uptake ( _VO2) kinetics and the energy
systems’ contribution at 97.5, 100 and 102.5% of the maximal lactate steady state (MLSS)
swimming intensity. Ten elite female swimmers performed three-to-five 30 min submaximal
constant swimming bouts at imposed paces for the determination of the swimming velocity
(v) at 100%MLSS based on a 7 x 200 m intermittent incremental protocol until voluntary
exhaustion to find the v associated at the individual anaerobic threshold. _VO2 kinetics (cardi-
odynamic, primary and slow component phases) and the aerobic and anaerobic energy con-
tributions were assessed during the continuous exercises, which the former was studied for
the beginning and second phase of exercise. Subjects showed similar time delay (TD)
(mean = 11.5–14.3 s) and time constant (τp) (mean = 13.8–16.3 s) as a function of v, but
reduced amplitude of the primary component for 97.5% (35.7 ± 7.3 mL.kg.min-1) compared
to 100 and 102.5%MLSS (41.0 ± 7.0 and 41.3 ± 5.4 mL.kg.min-1, respectively), and τp
decreased (mean = 9.6–10.8 s) during the second phase of exercise. Despite the slow com-
ponent did not occur for all swimmers at all swim intensities, when observed it tended to
increase as a function of v. Moreover, the total energy contribution was almost exclusively
aerobic (98–99%) at 97.5, 100 and 102.5%MLSS. We suggest that well-trained endurance
swimmers with a fast TD and τp values may be able to adjust faster the physiological
requirements to minimize the amplitude of the slow component appearance, parameter
associated with the fatigue delay and increase in exhaustion time during performance, how-
ever, these fast adjustments were not able to control the progressive fatigue occurred
slightly above MLSS, and most of swimmers reached exhaustion before 30min swam.
PLOS ONE | DOI:10.1371/journal.pone.0167263
February 28, 2017
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OPEN ACCESS
Citation: Pelarigo JG, Machado L, Fernandes RJ,
Greco CC, Vilas-Boas JP (2017) Oxygen uptake
kinetics and energy system’s contribution around
maximal lactate steady state swimming intensity.
PLoS ONE 12(2): e0167263. doi:10.1371/journal.
pone.0167263
Editor: Juan Sastre, Universitat de Valencia, SPAIN
Received: February 16, 2016
Accepted: November 11, 2016
Published: February 28, 2017
Copyright: © 2017 Pelarigo 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 paper and its Supporting Information
files.
Funding: This investigation was supported by
grants of the Capes Foundation, Ministry of
Education of Brazil (BEX: 0536/10-5): JGP and
project PTDC/DES/101224/2008 (FCOMP-01-
0124-FEDER-009577): JPVB RF.
Competing interests: The authors have declared
that no competing interests exist.
Introduction
An important aspect of aerobic endurance performance is the ability to sustain the highest per-
centage of maximal oxygen uptake (% _VO2max) as long as possible. In this sense, coaches and
swimmers have used the % _VO2max in different submaximal intensities to control, prescribe
and improve sports training [1]. Additionally, scientists have shown that the _VO2 kinetics
analysis may help to understand the physiological adjustments produced over time by the ath-
letes in several sports, allowing them to maintain a high % _VO2max in a physiological steady-
state during aerobic endurance performance [2–4].
Meanwhile, the scientific community has mainly described the _VO2 kinetics in three differ-
ent intensity domains during continuous exercise. First, the moderate domain is described as
the exercise intensities in which a state steady for _VO2 is achieved within 3 min of constant
exercise [5]. Subsequently, the heavy domain is described as the exercise intensities in which
_VO2 slow component should be evident, causing a delay on the achievement of the _VO2
steady-state during exercise [2]. Last, the severe domain is described as the exercise intensities
in which _VO2 is elevated compared to rest values and continue to increase over time, leading
to attain the _VO2max [6, 7].
Maximal lactate steady state (MLSS) is considered one of the main relevant parameters for
prescription and improvement of aerobic endurance performance, once it has been assumed
as the limit intensity at which, during prolonged and submaximal exercise, the metabolic
energy is produced mainly by the aerobic metabolism of pyruvate and glycolysis [8, 9]. More-
over, MLSS is identified as the maximal intensity that can be maintained over time without the
lactate production exceeding removal more than 1 mmol.L-1, and considered gold-standard
method for the evaluation of aerobic capacity [10–12].
Once maximal velocity where a steady-state is found represents a fundamental physiologi-
cal border, subtle changes in this intensity could likely modify _VO2 kinetics response. For
instance, when the exercise is performed at intensities slightly below MLSS, a physiological
steady state is sustained for both blood lactate concentration [La-] and _VO2 as a function of
time [6, 7, 13]. On the other hand, at intensities above the MLSS, a significant increase in [La-]
and _VO2 is likely to be observed throughout time [3, 7, 8, 12], leading to fatigue and voluntary
exhaustion [3, 4, 14]. Moreover, the swimming MLSS determination needs a short time of
interruption for the blood collection during the 10th minute of exercise for the analysis of [La-
], and then, a resumption of exercise to complete the test. Thus, it seems to be fundamental to
examine the behavior of _VO2 kinetics not only the beginning of exercise, but too after the
resumption of exercise throughout exercise to better understanding of the entire process of the
swimmer physiological response along the exercise.
_VO2 kinetics has been studied in different sports over the last decades [2, 6, 15], and there
are relevant number of researches based on [La-] and gas exchange at intensities related to
MLSS [8, 13, 14]. However, no study has evaluated _VO2 kinetics at (and around) the MLSS
intensity. Thus, our purpose was to examine _VO2 kinetics and the energy systems’ contribu-
tion at 97.5, 100 and 102.5%MLSS in swimming. It was hypothesized that at 97.5%MLSS, _VO2
kinetics adjustments may not be so evident such as 100 and 102.5%MLSS. It was further
hypothesized that even at the 100%MLSS intensity, swimmers may also have to adjust _VO2
kinetics during the exercise, once this intensity would lead to voluntary exhaustion over time.
On the other hand, at the intensity of 102.5%MLSS, _VO2 kinetics may be compromised by
fatigue, requiring faster time adjustments for time delay and time constant, and higher _VO2
amplitudes either for primary or slow components compared to lower exercise intensities. We
Oxygen kinetics and aerobic endurance performance
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further intended to assess _VO2 kinetics of the second phase of exercise, starting after the collec-
tion of [La-] and resumption of exercise (from 10th min to the exercise end—final exercise),
hypothesizing that these parameters could be faster than without previous exercise. Moreover,
as MLSS may be maintained for long time period without continuous [La-] accumulation, as
well as a submaximal exercise, the energy supply should be mainly supported through the aer-
obic system for the swimming intensities of ± 2.5% around MLSS.
Material and methods
Ten elite female swimmers volunteered and gave written informed consent (or parent/guard-
ian when subjects were under 18yrs) to participate in the present study, which was approved
by the Ethics Committee of Faculty of Sport from the University of Porto and performed
according to the Declaration of Helsinki. The swimmers were (mean ± SD) 17.6 ± 1.9 years of
age, 1.70 ± 0.05 m height, 61.3 ± 5.8 kg body mass, 15.5 ± 2.9% body fat mass, and 54.9 ± 6.7
mL.kg.min-1 _VO2max, specialized in middle- and long-distance swimming events. The subjects
had, at the least, seven years of experience as competitive swimmers and their mean perfor-
mance over a 400m freestyle swim was 88.0 ± 3.4% of the short course word record.
The test sessions were performed in a 25 m indoor swimming pool. Air humidity was main-
tained nominally between 40–60%, and pool water temperature between 27–28˚C. Swimmers
were advised to refrain from intense training at least 24 h before the experimental sessions.
The tests were conducted within a seven day period, at the same time of the day (± 2 h), mini-
mizing the circadian rhythm effects. Previously to the test sessions, swimmers performed a
1000 m warm-up at low/moderate intensity. The tests were performed in front crawl, with in-
water starts and open turns, without relevant underwater glides. A 24 h interval was imposed
between all tests.
Initially, swimmers performed an intermittent incremental protocol until voluntary
exhaustion to find the velocity (v) corresponding to the individual anaerobic threshold
(IAnT). The distance covered in each step was 200 m, with v increases of 0.05 m.s-1 and 30 s
rest intervals between each swim [16]. According to these authors, the predetermined v of the
last step was defined as the currently best expected performance for the subjects’ 400 m front
crawl, and then used to define all the v steps for the incremental test. The IAnT was assessed
by the relationship between [La-] and v using a curve fitting method, and considered the inter-
ception point between linear and exponential regressions to determine the accurate v where
[La-] increased exponentially [16, 17].
Subsequently, each swimmer performed three-to-five 30 min submaximal constant swim-
ming bouts at imposed paces to determine the highest v where a MLSS was achieved (100%
MLSS). The first trial was performed at the v corresponding to IAnT; and, if a steady state or a
decrease in [La-] was observed, further subsequent trials with 2.5% higher velocities were per-
formed until no [La-] steady state could be maintained [14]. Following this study, if the first
trial resulted in a clearly identifiable increase of the [La-], and/or could not be sustained due to
exhaustion, further trials were conducted with reduced velocities. MLSS was defined as the
[La-] that increased by no more than 1 mmol.l-1 between the 10th and 30th min of the test [9].
Earlobe capillary blood samples (5 μL) were collected: (a) at rest and in the first 30 s after
each step of the incremental test, immediately after exhaustion, and at each 2 min of recovery
(until the [La-] recovery peak was found); and (b) at rest, 10 and 30th min (or voluntary
exhaustion) of each continuous bout (Lactate Pro, Arkray, Inc., Kyoto, Japan).
The v was set and maintained using a visual underwater pacer (GBK-Pacer, GBK Electron-
ics, Aveiro, Portugal), with lights located each 2.5 m apart by a light strip on the bottom of the
pool. Swimmers followed the flashing lights to maintain the predetermined velocities. and
Oxygen kinetics and aerobic endurance performance
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were instructed to keep their heads above each visual signal. Exhaustion was defined when the
swimmers remained 5 m behind the lights.
_VO2 was measured by a telemetric portable gas analyzer (K4b2, Cosmed, Italy) in both
tests, connected to the swimmer by a low hydrodynamic resistance respiratory snorkel and
valve system (New AquaTrainer1, Cosmed, Italy). This system has been previously validated
[18] and used in similar studies [15]. The device was calibrated for minute ventilation ( _VE)
with a calibrated syringe (3 L) and the O2 and CO2 analyzers with standard calibration gases
(16% O2 and 5% CO2) before each test. In all tests, _VO2 data were analyzed and errant breaths
occurred by swallow water and/or saliva, sighs and coughs were excluded. Afterwards, _VO2
values were measured in mean ± 3 SD and outside values were removed. Subsequently, the
breath-by-breath data were linearly interpolated to provide five-by-five s values, and smoothed
using three breath averages [15, 19]. Heart rate (HR) was monitored and registered continu-
ously by a HR monitor system (Polar Vantage NV, Polar electro Oy, Kempele, Finland) and
transferred in real time, through a telemetric signal, to the K4b2 device. The HR values were
also averaged every 5 s intervals.
The average _VO2 values were analyzed by a nonlinear least squares algorithm to fit the data
through MatLab 7.0 Software (MathWorks, Natick, MA). The mathematical model consisted
of two (cardiodynamic and primary components) or three (cardiodynamic, primary and slow
components) exponential models. An F-Test (p < 0.05) was used to evaluate whether the two
or three exponentials models provided the best fit to each data set.
_VO2 ðtÞ ¼ _VO2 baseline þ Ac ½1 using multivariate ANOVA and examined by the intensity and previous exercise effects. The v
and [La-] values were performed using the univariate ANOVA. All analyses were conducted
for repeated measures, complemented with the Bonferroni correction post-hoc test with a sig-
nificance level of p < 0.05.
Results
All swimmers performed 30 min when swimming at 97.5 and 100%MLSS, but eight swimmers
were not able to maintain the predetermined v during 30 min at 102.5%MLSS, reaching volun-
tary exhaustion at 19.3 ± 4.9 min. The average v and % _VO2max values were different in between
the three swim intensities, with 97.5%MLSS slowest and lowest, and 102.5%MLSS fastest and
highest (F2,18 = 2560.200, p < 0.001, p
2 = 0.996; F2,18 = 15.538, p < 0.001, p
2 = 0.633, respec-
tively) (Table 1). [La-] and HR values for the three swim intensities are also shown in Table 1
with a higher values at 102.5%MLSS compared to 97.5 and 100%MLSS for [La-] (F2,18 =
18.123, p < 0.001, p
2 = 0.668), and at 102.5%MLSS compared to 97.5%MLSS for HR (F2,18 =
7.222, p < 0.005, p
2 = 0.445).
_VO2 kinetics parameters are presented in Table 2. Ap tended to increase with the swimming
intensity (v) during the initial exercise, but differences were only noticed comparing 100 and
102.5%MLSS to 97.5%MLSS (F2,18 = 8.249, p < 0.05, p
2 = 0.478). Meanwhile, Ap was similar at
final exercise for the three swim conditions (F2,18 = 1.167, p = 0.334, p
2 = 0.115). On the other
hand, Ap decreased as a function of previous exercise for the three swims bouts. TDp, τp and
MRT were similar as function of v at initial exercise and final exercise during the three swim-
ming conditions. However, when analyzed the swim bouts as a function of previous exercise,
TDp decreased for the 97.5%MLSS, but the values remained similar for 100 and 102.5%MLSS;
τp decreased for all swim intensities, and MRT decreased for the 97.5 and 102.5%MLSS, but
remained similar for 100%MLSS.
The both measured _VO2baseline at initial exercise (F2,18 = 2.389, p = 0.120, p
2 = 0.210) and
final exercise (F2,18 = 1.034, p = 0.376, p
2 = 0.103) were similar in between the three swim con-
ditions, but _VO2baseline increased as a function of previous exercise (initial to final exercise) for
all continuous intensities (F1,9 = 68.311, p < 0.001, p
2 = 0.884). Ac was similar as a function of v
for both initial exercise (F2,18 = 0.134, p = 0.876, p
2 = 0.015) and final exercise (F2,18 = 1.974,
p = 0.168, p
2 = 0.180). Moreover, at 97.5%MLSS, Ac was lower comparing initial and final exer-
cise, but values remained similar for 100 and 102.5%MLSS.
As of _VO2 kinetics was observed for all tested swimming intensities and testing phases (ini-
tial and final exercise) only in two out of ten subjects. In one subject As was not observed. The
As was observed for 6 swimmers during initial exercise and 8 swimmers during final exercise
at 97.5%MLSS, for 6 swimmers during initial exercise and 7 swimmers during final exercise at
100%MLSS, and for 9 swimmers during initial exercise and 5 swimmers during final exercise
Table 1. Mean (SD) values of swimming velocity (v), blood lactate concentrations ([La-]), heart rate
(HR), and percentage of maximal oxygen uptake (%VO2max) are shown at 97.5, 100 and 102.5% of the
maximal lactate steady state (MLSS) (N = 10).
97.5%MLSS
100%MLSS
102.5%MLSS
v (m.s-1)
1.21 (0.07)
1.24 (0.07)1
1.27 (0.07)1,2
[La-] (mmol.L-1)
1.48 (0.39)
1.89 (0.77)
2.97 (0.87)1,2
HR (beats.min-1)
167.1 (15.0)
173.6 (9.7)
179.3 (9.2)1
% _VO2max (%)
78.9 (8.7)
84.7 (3.8)1
90.9 (4.6)1,2
1,2 Values different from 97.5 and 100%MLSS, respectively (p < 0.05).
doi:10.1371/journal.pone.0167263.t001
_
Oxygen kinetics and aerobic endurance performance
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at 102.5%MLSS. The As values are presented in Table 3. As tended to increase with swimming
intensity during initial exercise, but keeping constant during final exercise whatever the inten-
sity considered; however no statistical analysis was applied, once the occurrence of the As was
apparently chaotic among swimmers both considering swimming intensities and phases of
testing (initial and final exercise).
The relative energy contribution for each one of the three swim intensity bouts is shown in
Fig 1. The aerobic energy contribution decreased (F2,18 = 15.254, p < 0.001, p
2 = 0.629) and the
anaerobic energy increased (F2,18 = 15.254, p < 0.001, p
2 = 0.629) at 102.5%MLSS compared to
97.5 and 100%MLSS.
Discussion
The purposes of this study were to examine the _VO2 kinetics responses during constant-veloc-
ity swims at intensities of 97.5, 100 and 102.5%MLSS, the effect of previous exercise on the
parameters of _VO2 kinetics, and the contribution of the energetic systems at the three
Table 2. Mean (SD) values of VO2 kinetics parameters at velocities of 97.5, 100 and 102.5% of the maximal lactate steady state (MLSS) for the
beginning of exercise until the break of swim for blood collection (initial exercise), and the second phase of exercise, starting after blood collec-
tion (final exercise) (N = 10).
97.5%MLSS
100%MLSS
102.5%MLSS
Initial exercise
Final exercise
Initial exercise
Final exercise
Initial exercise
Final exercise
VO2 baseline (mL.kg-1.min-1)
7.2 (2.1)
16.0 (5.3)a
6.0 (1.0)
17.4 (5.7)a
6.4 (0.8)
18.8 (5.8)a
Ac (mL.kg-1.min-1)
16.4 (5.9)
10.4 (4.9)a
16.1 (7.1)
14.2 (5.4)
15.1 (6.5)
14.9 (5.7)
Ap (mL.kg-1.min-1)
35.7 (7.3)
26.3 (7.4)a
41.0 (7.0)1
28.3 (5.2)a
41.3 (5.4)1
29.8 (5.5)a
TDp (s)
14.3 (5.5)
12.0 (5.3)a
12.4 (8.1)
11.9 (4.9)
11.5 (6.8)
11.1 (4.7)
τp (s)
16.3 (5.4)
10.8 (4.7)a
13.8 (4.5)
9.7 (4.5)a
16.0 (5.8)
9.6 (5.3)a
MRT (s)
30.6 (5.2)
22.8 (5.4)a
26.2 (6.8)
21.6 (4.6)
27.4 (8.5)
20.7 (5.2)a
Statistical analyses were described by intensity and previous exercise effect.
1 Values different from 97.5%MLSS for initial exercise.
a Values different from initial exercise (p < 0.05).
doi:10.1371/journal.pone.0167263.t002
Table 3. Individual and mean (SD) values of the amplitude of slow component (As) at velocities of 97.5, 100 and 102.5% of the maximal lactate
steady state (MLSS) for the beginning of exercise until the break of swim for blood collection (initial exercise), and the second phase of exercise,
starting after blood collection (final exercise) (N = 10).
As (mL.kg-1.min-1)
97.5%MLSS
100%MLSS
102.5%MLSS
swimmer
Initial exercise
Final exercise
Initial exercise
Final exercise
Initial exercise
Final exercise
1
1.7
2.9
2.3
3.8
4.5
1.6
2
2.3
0.7
4.4
0
3.7
0
3
1.1
0
2.6
0
4.4
0
4
0
0
0
0
0
0
5
4.2
0.9
2.8
0.8
2.9
0
6
0
0.8
0
0.8
1.9
2.2
7
0
1.2
0
0.9
7.2
1.1
8
0
1.7
2.8
1.1
4.5
0
9
2.5
1.3
2.6
1.5
6.1
0.8
10
1.4
0
0
1.5
5.1
1.8
Mean (SD)
2.2 (1.1)
1.4 (0.8)
2.9 (0.8)
1.5 (1.1)
4.5 (1.6)
1.5 (0.6)
doi:10.1371/journal.pone.0167263.t003
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conditions. The main original findings were that increasing exercise intensity resulted in
greater primary amplitude of the _VO2 kinetics, in accordance with previous results in running
[22]. As demonstrated by other studies [23–25], the previous exercise may increase the ampli-
tude of the primary component and accelerate _VO2 kinetics (i.e., MRT) during the subsequent
exercise. There was a significant increase in the anaerobic contribution when swimming above
MLSS. However, the aerobic energetic system contribution corresponded to ~99% of the total
energy demand of the exercise in all exercise conditions analyzed in this study.
In sports science, _VO2 kinetics have added the understanding of physiological adjustments
over time [2–4], such as muscle metabolism and systemic oxygen transport [26]. Moreover,
one of the most relevant exercise intensities in swimming for aerobic training, prescription
and evaluation is the v at which MLSS is obtained, being considered the direct and gold-stan-
dard method for the evaluation of aerobic capacity [8, 10–12, 14]. Thus, both aspects ( _VO2
kinetics and MLSS) are decisive for the understanding of energy supply and oxidative metabo-
lism supporting muscular exercise. Therefore, our purpose was to examine the amplitude and
time adjustments of _VO2 kinetics during swims at intensities of 97.5, 100 and 102.5%MLSS,
exploring the effects of small prescriptions variations on swimming oxidative physiology.
The main findings were: (a) Ap tended to increase with swimming v for the initial phase of
exercise, despite differences were only noticed comparing 100 and 102.5%MLSS to 97.5%
MLSS. Meanwhile, Ap was similar at the final phase of exercise during the three swim condi-
tions. However, Ap decreased as a function of previous exercise for the three swim intensities;
(b) TDp, τp and MRT were similar irrespective of v both at initial and final exercise; (c) regard-
ing the effect of previous exercise comparing initial and final exercise for the three swimming
intensities, TDp decreased for the 97.5%MLSS, but was similar for 100 and 102.5%MLSS, τp
decreased for all swim intensities, and MRT decreased for the 97.5 and 102.5%MLSS, but was
similar for 100%MLSS; (d) although As was not evident for all swimmers during the three
swimming conditions, it tended to increase with intensity during initial exercise, remaining
constant during final exercise; (e) Ac was similar both for the initial and final exercise compar-
ing the three swim intensities, but was lower during final exercise compared to initial exercise
at 97.5%MLSS, and was similar at 100 and 102.5%MLSS; (f) aerobic and anaerobic energy con-
tributions were different at 102.5%MLSS compared to lower swim velocities; (g) at the three
Fig 1. Mean ± SD of aerobic and anaerobic energy relative contribution values at velocities corresponding to 97.5, 100
and 102.5% of the maximal lactate steady state (MLSS).
doi:10.1371/journal.pone.0167263.g001
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swim intensities, the aerobic contribution values were higher than 98% of the total energy
input.
The _VO2 values in the present study were directly measured breath-by-breath throughout
time for the three swim intensities. Subsequently, the _VO2 data were fitted through mathemat-
ical modelling as previously applied in swimming for maximal and submaximal exercises [15,
19, 27–30]. Some studies have reported _VO2 kinetics at intensities near the maximal v where a
steady state in swimming is found (MLSS) [27–29], however we are unaware of a study that
has evaluated and compared _VO2 kinetics at or around the MLSS in swimming. Most of previ-
ous studies reported in sports science [2, 15, 19, 27–31] have studied _VO2 kinetics at maximal
and submaximal intensities, demonstrating the fundamental role of _VO2 kinetics to under-
stand the physiological mechanisms underpinning the dynamics of the aerobic response at dif-
ferent exercise intensities. Thus, the understanding of the _VO2 kinetics throughout time may
aid the evaluation of aerobic capacity and prescription of specific training sets during these
fundamental training intensities around MLSS.
The 100%MLSS v values reported in this study are in accordance with those reported in
previous ones [13, 14, 32], in spite of the fact that most of the swimmers examined in the previ-
ous studies were male when compared with the female subjects of the present study. Despite
higher v values at a given relative intensity are expected to be higher for male than female
counterparts of similar training level [33], the sex similitude comparing our results with litera-
ture could likely be explained by a higher technical and biomechanical proficiency of our
female swimmers when compared to the male swimmers of the previous studies. Indeed, the
% _VO2max at 100%MLSS (85 ± 4%) observed in the present study for women is similar to previ-
ously reported data for men (86.1% _VO2peak) [34], suggesting similar levels of aerobic capacity
development, even the _VO2max= _VO2peak being higher in the previous study (mean = ~83 mL.
kg-1.min-1) when compared with our results (54.9 ± 6.7 mL.kg-1.min-1). Meanwhile, the mean
HR value at 100%MLSS was 174 ± 10 beats.min-1 in the present study, values which were simi-
lar to the previous reported in literature [32, 34], as expected by the comparable age of
samples.
Moreover, the [La-] at 100%MLSS (1.89 ± 0.77 mmol.L-1) in the present study were lower
when compared to swimming literature (2.8–3.3 mmol.L-1) [14, 34, 35]. These lower [La-] val-
ues may be explained by sex differences for similar levels of aerobic capacity development,
with expected lower values for women due to lower body mass and lean muscle mass com-
pared to men [36]. Furthermore, women have showed lower testosterone concentration com-
pared to men [37] during aerobic endurance exercise [33, 36], suggesting different metabolic
contributions between carbohydrates and fat during long-distance exercise [33, 38], and sup-
porting comparable lower [La-].
Since the early research on _VO2 kinetics [39] until up to date, the time constant (τ) has
been studied in sports science in the attempt to comprehend the physiological adjustments
during the non-steady state period at the beginning of exercise due to the increase of metabolic
demand. In the present study, the τp values were similar between intensity levels for the initial
exercise phase (mean = 15.4 ± 5.2 s) and final exercise phase (mean = 10.0 ± 4.7 s), but the val-
ues decreased with previous exercise for the three swim conditions. This is particularly relevant
for training practice, underlining the influence of previous exercise on the subsequent meta-
bolic dynamics. In all studied exercise intensities, the τp in the present study showed similar
values compared than those previously reported in swimming (~15–20 s) [27–29], cycling [40,
41], rowing [42], and running [43, 44]. Thus, those values reported for intensities up to and
above the MLSS seem to behave similarly as expected, based on the previous knowledge on the
Oxygen kinetics and aerobic endurance performance
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February 28, 2017
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_VO2 kinetics during different intensity domains for well-trained athletes. Indeed, a faster
attainment of a steady state and a reduction in the oxygen deficit are associated to the fatigue
delay and increase in exhaustion time, being well trained athletes able to perform at higher
intensities with lower requirements of anaerobic energy during the transition from rest to
exercise [5]. Hence, the lower τp values reported in this study when compared to previously
published ones regarding physiological adaptations induced by aerobic endurance training
confirm the highly endurance training status and specialization (endurance athletes) of our
swimmers [5, 44].
Partially in contrast with previous literature that showed the existence of the As at these
exercise intensities [2, 4, 5], in the present study it has shown to occur chaotically during the
three swimming conditions, with very diverse individual occurrence profiles; however, observ-
ing the sample data a tendency to As increase as a function of intensity was observed (2.2 ± 1.1,
2.9 ± 0.8 and 4.5 ± 1.6 mL.kg-1.min-1, respectively for 97.5, 100 and 102.5%MLSS), but only
during initial exercise, not during the final phase after metabolic adaptation already occurred.
Besides, only two swimmers showed As occurrence in all trials both at the initial and final exer-
cise phases, and one swimmer did not show any As during all the swimming efforts and phases.
It is worthy to emphasize the curiosity of that particular swimmer being a national record
holder (800 and 1500m) and the best endurance swimmer of the sample. These partially con-
tradictory findings could be explained, at least in part, by the specific physiological adaptations
occurred through the highly endurance training status for our swimmers, such as faster τp
[44], possible increase in the mitochondrial content of the cell [45], beyond also possible alter-
ations in the mitochondrial sensitivity to the respiration regulators [46], and the fact of these
endurance athletes might have mainly type I muscle fibers [45]. Thus, our endurance swim-
mers with fast _VO2 kinetics would be able to adjust faster the physiological requirements for
aerobic performance during the high intensity aerobic exercises, minimizing the As demand.
In addition, the appearance of the As is normally explained by a phenomena that may be atten-
uated in our very specialized sample, namely the recruitment of type II fibers with fatigue [47],
after which the magnitude of As has been correlated with the rise of [La-] [2, 45]. Thereby, the
absence of significant As in the present study may be likely explained by the high-level of
endurance training of the sample [48].
Moreover, to reinforce the predominance of aerobic energy system during the three swim
conditions around MLSS, the present study determined the total energy contribution at each
one of the studied exercise intensities. At all swimming intensities up to and above MLSS, the
aerobic energy contribution was higher than 98% of the total energy contribution; however
there were significant differences between the highest and the lower v regarding aerobic and
anaerobic energy contributions. This study was the first study to show the energy contribution
during intensities at and around MLSS directly measured breath-by-breath in swimming,
which highlights that even at intensities above MLSS; the total energy contribution was mainly
and almost exclusively controlled by the oxidative bioenergetics system.
Conclusions
The present study showed that well-trained endurance swimmers with a fast component of
_VO2 kinetics, i.e. an abrupt and fast increase in _VO2 response, and low [La-] may be able to
adjust faster the physiological requirements during intensities up to and slightly above MLSS
to minimize the appearance of the slow component of _VO2 and reduce the oxygen deficit,
both parameters are associated to the fatigue delay and the increase in exhaustion time, key
factors to endurance performance. however, these fast adjustments were not able to control
the progressive fatigue occurred slightly above MLSS, and most of swimmers reached
Oxygen kinetics and aerobic endurance performance
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February 28, 2017
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exhaustion before 30min swam. Moreover, the data shows that the aerobic energy contribution
at intensities up to and slightly above MLSS plays a fundamental role controlling almost exclu-
sively the required energy supply.
Supporting information
S1 File. Values of physiological parameters at 97.5, 100 and 102.5% of the maximal lactate
steady state (MLSS) (N = 10).
(PDF)
S2 File. Values of VO2 kinetics parameters at 97.5, 100 and 102.5% of the maximal lactate
steady state (MLSS) (N = 10).
(PDF)
Acknowledgments
This investigation was supported by grants of the Capes Foundation, Ministry of Education of
Brazil (BEX: 0536/10-5), and project PTDC/DES/101224/2008 (FCOMP-01-0124-FEDER-
009577).
Author Contributions
Conceptualization: JGP JPVB CCG RJF.
Data curation: JGP LM JPVB CCG RJF.
Formal analysis: JGP LM JPVB.
Funding acquisition: JPVB RJF.
Investigation: JGP JPVB CCG RJF LM.
Methodology: JGP JPVB LM CCG RJF.
Project administration: JGP JPVB RJF.
Resources: JGP RJF JPVB.
Software: LM JGP JPVB.
Supervision: JGP JPVB CCG RJF LM.
Validation: JGP LM JPVB CCG RJF.
Visualization: JGP JPVB CCG RJF LM.
Writing – original draft: JGP JPVB RJF CCG LM.
Writing – review & editing: JGP JPVB CCG RJF LM.
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Oxygen uptake kinetics and energy system's contribution around maximal lactate steady state swimming intensity.
Pelarigo, Jailton Gregório,Machado, Leandro,Fernandes, Ricardo Jorge,Greco, Camila Coelho,Vilas-Boas, João Paulo