This study assessed the accumulated oxygen deficit (AOD) during 50, 100, and 200 m front-crawl performances to compare the responses between sexes and analyse the effect of lean body mass (LBM). Twenty swimmers (16.2 ± 2.8 years, 61.6 ± 7.8 kg, and 48.8±11.2 kg LBM) performed 50, 100, and 200 m to determine accumulated oxygen uptake (V̇O2Ac). The swimmers also performed an incremental test from which five submaximal steps were selected to estimate the oxygen demand (V̇O2demand) from the V̇O2 vs velocity adjustment. V̇O2 was sampled using a gas analyser coupled with a respiratory snorkel. AOD was the difference between V̇O2demand and V̇O2Ac, and LBM was assessed by dual-energy absorptiometry. A two-way ANOVA evidenced an AOD increase with distance for both sexes: 19.7 ± 2.5 vs 24.9 ± 5.5, 29.8 ± 8.0 vs 36.5 ± 5.8, and 41.5 ± 9.4 vs 55.2 ± 11.9 ml×kg−1, respectively for 50, 100, and 200 m (with highest values for females, P < 0.01). Inverse correlations were observed between LBM and AOD for 50, 100, and 200 m (r = -0.60, -0.38 and − 0.49, P < 0.05). AOD increased from 50 to 200 m distances for both sexes. However, females presented higher AOD values, which probably relates to the effect of reduced LBM on increasing the rate of oxygen deficit (i.e., anaerobic energy demand).
Article
Sex-Specific Effect on Accumulated Oxygen Deficit During Short and Middle-Distance Swimming Performance
https://doi.org/10.21203/rs.3.rs-1439614/v1
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Pulmonary oxygen uptake
oxygen deficit estimate
lean body mass
swimming performance
sex
- AOD increasing from 50 to 200 m was higher for female than male swimmers in all trials when expressed per unit of body weight, which seemed to be an effect of the longest time to perform each trial for women.
- AOD decreased from 50 to 200 m when analysed in a common unit of time elapsed during trials, with females showing higher values than males only in 200 m.
- The observed inverse relationship between AOD and lean body mass suggests that the higher oxygen deficit for female than male swimmers while performing short and middle-distances races might be accounted for the gender-related differences in lean mass.
- The main message is that the AOD is higher in female swimmers when performing short and medium distances in swimming, with differences observed both at the beginning (10 and 30 s) of the long (200 m) and at the end of the short events (50 and 100 m), which can be explained by the differences in muscle mass between males and females in view of the observation of the inverse association between AOD and lean body mass.
The energy demand during ≤ 60 s competitive swimming (the 50 and 100 m events) is mainly supplied by anaerobic energy sources (60–80%), while the aerobic metabolism contributes decisively at efforts > 120 s (200 m and longer) (Zamparo et al., 2000; Hellard et al., 2018; Zacca et al., 2020; Almeida et al., 2020). Earlier researches on swimming anaerobic requirements have reported the total oxygen debt and the peak blood lactate concentrations ([La−]) in high-intensity performance at 15–18 LO2 and 12–18 mmol×L− 1 as the reference range of values (Holmér 1979; Vescovi et al., 2011). Furthermore, the latest studies that assessed energetics during high-intensity swimming bouts, particularly using the accumulated oxygen deficit (AOD) method, but not only, corroborated the evidence that anaerobic metabolism is a fundamental source of energy released during short- and middle-distances swimming performances (Peyrebrune et al., 2012; Zacca et al., 2020; Massini et al., 2021).
In fact, the 100, 200, and 400 m front crawl performed at 140, 127, and 108% of maximal oxygen uptake (V̇O2max) require a contribution of AOD achieving 45–50, 30–35 and 15–20% (respectively) of the total energy demand, which is however, lower for swimmers with a higher conditioning level (Troup et al., 1992; Fernandes et al., 2006). Complementarily, at the 30, 60, and 120–180 s swims (corresponding to the 50, 100, and 200 m events), AOD contributions attained 65–70, 50–55, and 30–35% of total energy demand (Ogita et al., 2003), which are AOD rates higher than those estimated for the 100 and 200 m trial performances (Reis et al., 2010), but aligned to the contribution reported for similar time performances in running (Ramsbottom et al., 1994; Spencer and Gastin, 2001; Duffield et al., 2005), as well as to the anaerobic contribution reported for the same distances in swimming (Zamparo et al., 2000; Figueiredo et al., 2011).
However, the eventual dissimilarities on male vs female AOD profiles have not yet been studied, precluding to match the anaerobic-specific training needs per sex. The available information is limited to the swimming economy profile (e.g., Fernandes et al., 2005) and maximal anaerobic capacity estimated through the maximal value of AOD, with values attaining 53.3 vs 42.7 ml×kg− 1 for male and female swimmers at 120 and 180 s exertions (corresponding to the 200 and 300 m events; Ogita et al., 1996). The difference between sexes is justified by the larger active muscle mass in males, but basic statements about sex-related differences affecting AOD values (like lean body mass) are still lacking.
Considering that AOD is assessed by subtracting the accumulated oxygen uptake (V̇O2Ac) from the predicted O2 demand (V̇O2demand) in exercises performed at intensities higher than that corresponding to V̇O2max (i.e., > iV̇O2max, Bangsbo et al., 1993), then the AOD sex-specific response at such supramaximal intensities might be an effect of the limited O2 supply among those with reduced lean body mass, therefore a reduced V̇O2Ac is expected for female swimmers. This preliminary speculation is supported by the statements that females have limited capacity to deliver O2 to the working muscles at maximal V̇O2 rates (Falz et al., 2019; Koons et al., 2019) and that blood volume and haemoglobin mass are closely related to lean body mass in young and healthy individuals (Falz et al., 2019), therefore such assumption as higher AOD values are expected for female swimmers during 50, 100, and 200 m front crawl, as a function of low lean body mass, allows us to hypothesise that lean body mass relates negatively to AOD.
In swimming, another factor affecting AOD is the effect of hydrodynamics on V̇O2 vs velocity slope (Fernandes et al., 2005; Zamparo et al., 2011), which is the key factor modifying V̇O2demand estimation between subjects and determining differences of AOD values in running and cycling (Noordhof et al., 2010). However, the hydrodynamics effect on V̇O2 vs the linear velocity relationship in swimming relates to conditioning level and not a sex-based characteristic (Fernandes et al., 2005, 2006), therefore the AOD sex-specific response (when observed) probably relies on the lower V̇O2Ac in female than male swimmers. To address the effect of sex on AOD at the 50, 100, and 200 m front crawl performances, the current study aimed to estimate and compare AOD between male and female swimmers at the total and common partial time elapsed (i.e., isotimes) and also determine the relationship between AOD and lean body mass in short and middle-distance events.
Table 1 displays the values of the variables obtained from the incremental protocol and the 50, 100, and 200 m maximal trials. The V̇O2peak relative to body weight did not differ between male and female swimmers (P = 0.34, g = 0.42 [small]), although a higher vV̇O2peak was observed in the males (P = 0.01, g = 1.18 [large]). The values of the constants (e.g., slope and intercept) for the V̇O2 vs velocity adjustment during the incremental protocol were similar between sexes (P = 0.36, g = 0.44 [small]) and P = 0.975, g = 0.01 [trivial], respectively). Complementarily, this adjustment showed a high linear coefficient (R2) (0.99 ± 0.006) for the steps encompassing the longest time (258.0 ± 20.7 s) and lowest exercise rate (63.4 ± 8.6%V̇O2peak) to the shortest time (208.4 ± 15.8 s) and highest exercise rate (91.2 ± 6.4%V̇O2peak). The 50, 100, and 200 m exertions were conducted at 128.3 ± 11.6 vs 126.3 ± 9.2, 114.2 ± 6.2 vs 117.3 ± 7.5, and 98.6 ± 5.9 vs 100.4 ± 6.0% of the vV̇O2peak for male and female swimmers, without differences between sexes (P = 0.42, η2p = 0.042 [small]).
| Men (n = 10) | Women (n = 10) | Total (n = 20) | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Mean ± SD | IC95% | SEM | Mean ± SD | IC95% | SEM | Mean ± SD | IC95% | SEM | |
| Step protocol | |||||||||
| V̇O2peak (ml×kg−1×min−1) | 58.8 ± 5.5 | 54.8–62.7 | 1.7 | 56.1 ± 6.7 | 51.1–60.9 | 2.1 | 57.4 ± 6.2 | 54.5–60.3 | 1.38 |
| vV̇O2peak (m×s−1) | 1.29 ± 0.07 | 1.24–1.34 | 0.02 | 1.21 ± 0.07 | 1.17–1.25 | 0.02 | 1.25 ± 0.08 | 1.21–1.29 | 0.02 |
| Slope (ml×kg− 1×m− 1) | 0.49±0.08 | 0.43–0.55 | 0.03 | 0.54±0.13 | 0.45–0.63 | 0.04 | 0.51±0.11 | 0.46–0.56 | 0.02 |
| Intercept (ml×kg− 1) | 12.6±4.6 | 9.3±15.9 | 1.45 | 12.6±2.9 | 10.5±14.7 | 0.92 | 12.6± 3.7 | 10.9±14.4 | 0.82 |
| 50 m | |||||||||
| Velocity (m×s− 1) | 1.66 ± 0.17*bc | 1.54–1.78 | 0.05 | 1.52 ± 0.08*bc | 1.46–1.57 | 0.03 | 1.59±0.15bc | 1.52–1.66 | 0.03 |
| AOD (L) | 1.37 ± 0.24bc | 1.19–1.54 | 0.08 | 1.33 ± 0.24bc | 1.16–1.50 | 0.07 | 1.35 ± 0.24bc | 1.24–1.46 | 0.05 |
| V̇O2Demand (L) | 2.07±0.24*bc | 1.90–2.25 | 0.08 | 1.81±0.26*bc | 1.62–1.99 | 0.08 | 1.94±0.28bc | 1.81–2.07 | 0.06 |
| V̇O2Ac (L) | 0.57±0.15*bc | 0.47–0.68 | 0.47 | 0.34±0.11*bc | 0.27–0.42 | 0.03 | 0.46±0.17bc | 0.38–0.54 | 0.04 |
| 100 m | |||||||||
| Velocity (m×s− 1) | 1.48 ± 0.12ac | 1.39–1.56 | 0.04 | 1.41 ± 0.07ac | 1.36–1.46 | 0.02 | 1.44±0.10ac | 1.40–1.49 | 0.02 |
| AOD (L) | 2.08 ± 0.67ac | 1.60–2.55 | 0.21 | 1.97 ± 0.29ac | 1.76–2.18 | 0.09 | 2.02 ± 0.50ac | 1.79–2.26 | 0.11 |
| V̇O2Demand (L) | 4.32±0.54*ac | 3.94–4.71 | 0.17 | 3.69±0.49*ac | 3.34–4.04 | 0.15 | 4.00±0.57ac | 3.73–4.28 | 0.13 |
| V̇O2Ac (L) | 2.04±0.32*ac | 1.81–2.27 | 0.10 | 1.52±0.28*ac | 1.32–1.72 | 0.09 | 1.78±0.40ac | 1.60–1.97 | 0.09 |
| 200 m | |||||||||
| Velocity (m×s− 1) | 1.27 ± 0.09 ab | 1.21–1.34 | 0.03 | 1.21 ± 0.08 ab | 1.15–1.26 | 0.02 | 1.25±0.09ab | 1.20–1.28 | 0.02 |
| AOD (L) | 2.87 ± 0.74ab | 2.34–3.40 | 0.24 | 2.99 ± 0.68ab | 2.50–3.48 | 0.22 | 2.93 ± 0.70ab | 2.60–3.26 | 0.17 |
| V̇O2Demand (L) | 9.00±1.12*ab | 8.20–9.80 | 0.35 | 7.60±1.07*ab | 6.83–8.36 | 0.34 | 8.30±1.28ab | 7.70–8.90 | 0.29 |
| V̇O2Ac (L) | 5.85±0.60*ab | 5.42–6.28 | 0.19 | 4.31±0.74*ab | 3.78–4.83 | 0.23 | 5.08±1.03ab | 4.60–5.56 | 0.23 |
Table 1: *** insert here***
Figure 1 illustrates the AOD profile at a given period of time and for the entire distance in 50, 100, and 200 m maximal front crawl trials. It is observed that there is a tendency to attain high AOD values as an effect of both the intensity and duration of the performances, i.e., AOD is greater at higher swimming speeds (50 and 100 m) due to the greater deficit at the beginning of the performance, but at long distances (200 m) there is greater accumulation with time. The effect of body mass on AOD values is depicted for each trial in Fig. 2 (Panel A), revealing differences (P = 0.04, η2p = 0.190 [large]) between: (i) distances, with AOD increasing from 50 to 100 m, 50 to 200 m, and 100 to 200 m in both male and female swimmers (all for P < 0.01); and (ii) sexes, with higher values for female swimmers in 50 m (P = 0.01), 100 m (P = 0.05), and 200 m (P = 0.01). The variability of the AOD estimates for the entire sample at 50, 100, and 200 m demonstrated low heterogeneity for the group (Table 1).
Figure 1: *** insert here***
Figure 2: *** insert here***
Inverse relations were observed between AOD and LBM for 50, 100, and 200 m trials (r = -0.60 [moderate], -0.38 [low] and − 0.49 [low], all for P ≤ 0.05), but when adjusted for sex no relationship was found. Since LBM values differed between male and female swimmers (IC95%: 52.9–62.9 vs 35.8–43.7 kg; P < 0.01), the previously observed correlation to AOD showed to be an effect of the differences in LBM between sexes.
Before controlled for sex, LBM inversely related with V̇O2demand in 50, 100, and 200 m trials (r = -0.56[moderate], -0.51 [moderate] and − 0.45 [low], P ≤ 0.05) and slope (r = -0.44[low], P = 0.03). After controlled for sex, LBM vs V̇O2demand relations at each distance (r = -0.51[moderate], -0.46 [low] and − 0.40 [low], respectively for the 50, 100, and 200 m, P ≤ 0.05) presented small reductions, while for LBM vs slope the correlation increased (r = -0.49 [low], P = 0.03). There were relationships between LBM and V̇O2Ac only when adjusted for sex (r = -0.41[low], -0.70 [high] and − 0.53 [moderate], respectively for the 50, 100, and 200 m, P ≤ 0.04).
By comparing AOD values at 10 (P = 0.81, η2p = 0.011 [medium]) and 30 s (P = 0.82, η2p = 0.011 [medium]) elapsed times during the 50, 100, and 200 m trials, it was possible to illustrate the effect of exercise intensity at each distance per sex (Fig. 2 Panel B and C). Both sexes reduced AOD values at 10 and 30 s from 50 to 100 m, 50 to 200 m, and 100 to 200 m (with P < 0.01 for all comparisons). No differences between sexes were observed at 10 and 30 s for 50 and 100 m trials. However, male swimmers presented lower values than females at 10 and 30 s in the 200 m (P = 0.02 at both isotimes).
The anaerobic energy contribution in short and middle-distance swimming is fundamental for higher level performances, but its analysis per sex remains unstudied. Thus, we have determined the AOD of male and female swimmers at the 50, 100, and 200 m front crawl distances, probably some of the most relevant events of the Olympic Games. The current study reported three unique findings: (i) absolute and relative AOD values increased from 50 to 200 m front crawl trials for both sexes, with female swimmers exhibiting higher values than males; (ii) AOD values at 10 and 30 s elapsed times in each distance-trial decreased for both sexes (concurrently with velocity reducing as distances increased), with higher values for female swimmers than males in the 200 m trial; and (iii) LBM and AOD values are inversely related for all distances, probably due to the differences in body composition between sexes.
Both groups showed time dependence for the AOD profile from 50 to 200 m front crawl trials, which is aligned to previous studies reporting AOD for swimming performances at 140, 127, and 108% V̇O2max (Troup et al., 1992) and for bouts lasting 30, 60, and 120 s (Ogita et al., 2003 and Peyrebrune et al., 2012). In these pioneer studies, conducted only with male swimmers, the AOD profile reaches its maximal hypothetical value of 3.2 LO2 when performing at 108% V̇O2max (Troup et al., 1992) or either during exhaustive trials performed at 100–110% vV̇O2max lasting 120–180 s (Ogita et al., 2003). In the current study, the mean absolute AOD values (in litres) for both sexes during the 200 m are close to the aforementioned maximal reference, and therefore, we evidenced that male and female swimmers only differed in AOD response when body mass differences are not taken in account.
Regarding the differences between sexes for AOD, only Ogita et al. (1996) reported the maximal AOD was higher for male (53–61 ml×kg− 1) than female swimmers (43–53 ml×kg− 1), and stated that AOD reaches its maximum value in swimming performances lasting 2–3 min, at a metabolic rate of 110% V̇O2peak. Although these results for maximum AOD values between sexes are unique in swimming, they are in line with the trend of values presented in other sports (Spencer and Gastin. 2001; Hill and Vingren, 2014; Weber et al., 2006). Despite the maximal AOD assessment is not in the scope of the current study, the AOD values for male and female swimmers during 200 m correspond to an overall energy demand approaching 107% V̇O2peak and 115% V̇O2peak (respectively), therefore the current data suggest that the 200 m might be an adjustable distance to demand the maximal AOD in female swimmers, while for males a longer distance at such metabolic rate would be advisable.
However, AOD increases over time, but its contribution to total V̇O2demand reduces as the period of swimming time is elongated, with values lower for male swimmers than females respectively in the 50 (65 vs 73%), 100 (47 vs 53%), and 200 m (32 vs 39%). These observed AOD rates of contribution are close to those for 30, 60, and 120–180 s reported by Ogita et al. (2003) and for 30 s tethered swimming bouts reported by Peyrebrune et al. (2012). Curiously, those rates for AOD contribution are also similar to those observed in cycling during 30, 60, and 120 s (60, 50, and 35%, respectively; Medbo and Tabata, 1989), and running the 400 (59% and 55%) and 800 m events (40 and 30%) for male and female participants (Duffield et al., 2005). Hence, these reports support the notion that the balance between AOD and V̇O2Ac in swimming is attained between 100 to 200 m, regardless of sex.
The results also showed that LBM related negatively to AOD (for each distance), V̇O2demand, and to the slope of V̇O2 vs velocity adjustment. While the LBM correlation to AOD reduced when controlled for sex-specific body composition, the V̇O2Ac, V̇O2demand, and the slope remained unchanged, enhanced, or became evidenced. These correlations suggest that swimmers with the greatest LBM can perform each distance with the highest oxidative energy release, which is supported by the lower V̇O2Ac and higher AOD for female swimmers when compared to males in each distance.
Studies relating muscle tissue mass to metabolic response also consider that the largest is the muscle mass engaged in exercise, the lowest is the intensity of fibre activation, reducing the glycolytic demand and increasing the oxidative energy supply (Beneke et al., 2001). Regarding sex-specific lean mass regionalisation, larger upper-limb muscle mass provides less peripheral restriction and higher O2 muscle extraction, increasing V̇O2Ac (Withers et al., 1991; Weber et al., 2006). Therefore, the current study corroborated the influence of muscle mass on AOD values, considering that sex-specific response is mandatorily lower among swimmers with greater LBM while performing trials at similar %vV̇O2peak during the same distance.
However, the findings that the maximal AOD values differed between males and females in running and cycling have been attributed to the specificity of sport demand and conditioning level, with reduced interference (4%) accounting for the sex difference regarding active muscle mass (Hill and Vingren, 2014). Nevertheless, the sex-specific amount of active muscle influences peak oxygen deficit in leg-cycling (Weyang et al., 1993). Furthermore, large muscle mass engagement also supports the findings that anaerobic capacity measured by the Wingate (30 s “all-out”) test with leg and arm ergometers differed between sexes only for upper-limbs, supporting the statement that body weight does not account for sex differences, exceptionally for body regions with distinct LBM distribution (Weber et al., 2006).
For the current study, both statements suggest that differences in body weight and LBM between sexes were associated with AOD increase in 50, 100, and 200 m. However, body composition differences between sexes neither constraints the absolute AOD values nor the rate of oxygen deficit (e.g., AOD measured at fixed elapsed times) during each bout, suggesting that female swimmers have higher AOD demand than males while performing supramaximal trials regardless of the distance and duration of the effort.
Regarding the slope, which is a rate relating V̇O2 to submaximal velocities, it is an index of the oxygen cost for the increment in exercise intensity (Green and Dawson, 1995; Pessôa Filho et al., 2017), which accounts for more than half of the variance in the AOD estimation (Medbo et al., 1988). In the current study, the difference between sexes for the slope was about 8.8%, with female swimmers showing higher values than males. The observed difference in slope between sexes might be considered not too large, when comparing with other studies in swimming that reported slopes differing from 13 to 25% between sexes (Fernandes et al., 2005; Pessôa Filho et al., 2017).
In general, male swimmers possess higher slope values than females when reported in absolute terms (i.e., ml×min− 1), which is a feature of high hydrodynamics drag during higher velocity for men (Fernandes et al., 2005). However, the current slope values were presented relative to body mass, and hence best aligned to the notion that higher cost for female swimmers might suggest a premature demand upon less economical fibre types while exercise intensity increases (Pessôa Filho et al., 2017), and therefore also aligned to the increased oxygen deficit and reduced exercise tolerance at such a high intensity condition (Weber et al., 2006). Notwithstanding, the effect of low LBM on O2 availability to muscles at high-intensity exercise (Falz et al., 2019) is also aligned to the notion of the earliest recruitment of fast-type fibres, and hence explains the inverse relationship of slope and V̇O2Ac with LBM observed in the current study. In addition, the difference between sexes regarding body fat content was also reported to have an effect on energy cost of running during middle-distance maximal performance (Hill, 1999).
A limitation could be related to the number of trials applied to the AOD assessment, which is not similar to the former AOD assessment. However, studies with similar procedures have been applied satisfactorily for submaximal steps during incremental tests for the assessment of AOD in swimming, running and kayaking (Reis et al., 2010; Duffield et al., 2005; Li et al., 2018). Also, the number of trials and the exercise intensities (e.g., %V̇O2peak) applied in the current study is in accordance with the recommendation to avoid the non-linearity of the slope and affect the robustness of the extrapolation of the V̇O2demand (Noordhof et al., 2010). The use of the New Aquatrainer® to measure the V̇O2Ac might be considered another limitation to reproduce physiological demand ecologically if considering the delays of the actual swimming velocity as an effect of turning and gliding constraints (Chaverri et al., 2016). However, the swimmer is enabled to stroke at a maximum rate when required, and therefore, task impairments with the New Aquatrainer® would not affect the muscle mass engagement, as well as the level of exertion while swimming (Ribeiro et al., 2016).
In conclusion male and female swimmers performed 50, 100, and 200 m with similar relative pacing above maximal aerobic velocity, but required different AOD values. The higher relative AOD values per unit of body weight in female rather than male swimmers might be explained by the sex-specific LBM content, since LBM has shown an inverse effect on all estimates for the assessment of AOD (i.e., V̇O2demand, V̇O2Ac, and slope). Although LBM plays a role in distinguishing the AOD response between sexes, future studies should better understand the influence of body composition on anaerobic conditioning after training planned to increase regional and total lean mass.
Subjects
Twenty swimmers (10 males and 10 females) volunteered to participate in the current study. Their main body characteristics were: 16.9±2.1 vs 15.5±3.1 years old, 179.5±7.3 vs 161.6±7.5 cm in height, 69.3±8.1 vs 54.4±6.8 kg of body mass, 12.2±3.1 vs 23.3±4.0% of body fat, and 57.9±7.0 vs 39.7±5.5 kg of lean body mass. The swimmers best front crawl performances at the 50, 100, and 200 m freestyle achieved 582±91 vs 533±62, 616±92 vs 530±72, and 607±93 vs 552±93 FINA points for male and female swimmers respectively. All participants (and their legal guardians when under 18 years old) signed an informed consent. This research was approved by the local Ethics Committee of São Paulo State University (CAEE: 54372516.3.0000.5398), which therefore supported that the procedures adhered to international and national laws for ethics principles in research practice with human participants.
Study design
After being familiarised with the experimental procedures, and after a standard low-moderate intensity warm-up (Zacca et al., 2019), the swimmers performed four testing sessions (separated by 24 h) in a 25 m indoor swimming pool (~28ºC water temperature and ~50% relative humidity) always at the same time of day. Firstly, they swum 50, 100, and 200 m maximal front crawl trials in randomised order, and afterwards performed an incremental intermittent protocol until exhaustion composed of 6 x 250 plus 1 x 200 m at 50, 60, 70, 80, 90, 95, and 100% of the velocity corresponding to the previous 200 m trial, with 30 to 60 s intervals between steps (Almeida et al., 2021). Participants avoided exhaustive training and caffeine/alcohol ingestion 24 h before the tests and were well fed and hydrated.
Measurements
The 50, 100, and 200 m trials and the incremental protocol used in-water starts and open turns (without underwater gliding), with the swimming speed of the incremental protocol steps being controlled visually through an underwater LED line (Pacer2SwimÒ, KulzerTEC, Aveiro, Portugal), previously applied to pace control in swimming (Zacca et al., 2019; Monteiro et al., 2020; Almeida et al., 2021). Gas exchange was sampled breath-by-breath using a gas analyser (K4b2® Cosmed, Rome, Italy) attached to a breathing snorkel (New AquaTrainer®, Cosmed, Rome, Italy), ensuring V̇O2 sampling accuracy (Ribeiro et al., 2016). Raw V̇O2 data were smoothed every three breaths, aligned for time, interpolated second-to-second and averaged every 30 s (Reis et al., 2012; Monteiro et al., 2020). V̇O2peak was considered as the higher moving average attained during the incremental protocol and its velocity (e.g., vV̇O2peak) corresponded to the step in which it was attained (Fernandes et al., 2005, 2006; Monteiro et al., 2020).
The V̇O2 vs velocity relationship during the incremental protocol was adjusted with a linear function (y = ax +b, where y is V̇O2, x is swimming velocity, a is the slope, and b is the intercept), a reliable procedure to estimate the V̇O2demand (Reis et al., 2010). For ensuring that each step lasted ~3-4 min, minimising extra V̇O2 occurrence and the non-linearity between V̇O2 response and velocity (Noordhof et al., 2010), only the five intermediate incremental protocol steps entered the model. This selection also aimed to elicit a V̇O2 demand close to an isocapnic condition to maintain V̇O2 aligned with the velocity increments (Pessôa Filho et al., 2017) and a 10-35 s V̇O2 kinetics time constant that is typical for low-moderate and heavy intensity domains (Almeida et al., 2020; Reis et al., 2012). The final V̇O2 response in each step was obtained by the last 30 s moving average value (Almeida et al., 2020).
The V̇O2Ac values over the 50, 100, and 200 m trials were obtained by integrating V̇O2 vs time response for each distance using Equation 1 (Almeida et al., 2020):
where t0 and tLim refer to each front crawl trial onset and final times. AOD was estimated by subtracting V̇O2Ac from V̇O2demand, considering 9% of O2 stores in blood and muscle (Medbo et al., 1988). From Equation 1, AOD was also calculated at 10 and 30 s isotimes for each 50, 100, and 200 m trial, considering t0 ® tLim10s and t0 ® tLim30s to determine V̇O2Ac over the first 10 and 30 s, respectively. V̇O2demand was estimated by extrapolation of the linear function between V̇O2 and velocity to the respective velocity at 50, 100, and 200 m trials, considering V̇O2baseline as a fixed intercept. The V̇O2demand for each isotime was estimated by limiting V̇O2 projection to 10 and 30 s elapsed during 50, 100, and 200 m trials. Blood was sampled (25 ml) during rest, at every interval of the incremental protocol (at 1, 3, 5 and 7 min of the recovery after each effort) for assessing [La-] values (using a YSL analyser, 2300 STAT, Yellow Springs). Dual-energy absorptiometry (DXA, HologicÒ, QDR Discovery WiÒ) was used to assess body composition, with APEXÒ software providing whole-body values for lean body mass (LBM, i.e., not including bone mineral content), and body fat percentage (%F).
Statistical Analysis
The Shapiro-Wilk and Mauchly tests verified data normality and sphericity. An independent t-test (2-tailed) compared sexes regarding body composition, V̇O2max, and vV̇O2max, with the corresponding effect size being calculated using Hedges g: <0.19 [trivial], 0.20–0.49 [small], 0.50–0.79 [medium], 0.80–1.29 [large], and >1.30 [very large] (Rosenthal, 1996). Two-way ANOVA (with Sidak as post-hoc) compared the effect of sex and exercise distances on AOD. The effect size was calculated using Partial eta squared (η2p), considering 0.0099 [small], 0.0588 [medium], and 0.1379 [large] (Cohen, 1988). The correlations between AOD, V̇O2demand, V̇O2Ac, slope, and lean mass were analysed by Pearson’s coefficient (r), with and without sex as a control variable, and classified as 0–0.29 [negligible], 0.3–0.49 [low], 0.5–0.69 [moderate], 0.7–0.89 [high], and 0.9–1.0 [very high] (Mukaka, 2012), with significance level being set at P ≤ 0.05.
Acknowledgements
The authors would like to express our gratitude to the swimmers for their time and effort and the swimming teams for making their infrastructures and staff available for the study. DMPF would like to thank São Paulo Research Foundation - FAPESP (PROCESS 2016/04544-3 and 2018/16706-3) for the partial financial support, and ME to the Foundation for Science and Technology, I.P. Grant/Award Number UIDB/04748/2020. AGM acknowledges the fellowship from Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES – Finance Code 001). The collaboration of T.A.F.A. was possible thanks to the scholarship granted from the Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES), in the scope of the Program CAPES-PrInt, process number 88887.310463/2018-00, Mobility number 88887.580265/2020-00.
Competing interest statement
The authors declare no competing interests.
Authors Contribution Statement
TAFA, JFR, FJBA and DMPF conceived and designed the research. DAM, AGM, TAFA and DMPF conducted the experiments. DAM, AGM, TAFA, JFR, MACE, FJBA, RJPF and DMPF reviewed and analysed the data. DAM, AGM, TAFA, JFR, MACE, FJBA, RJPF and DMPF wrote the first drafted of the manuscript and MACE, JFR, FJBA, RJPF and DMPF commented previous versions and wrote the final manuscript. All authors read and approved the manuscript.
Data availability
All data generated or analysed during this study are included in this published article, and in its supplementary information file.
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No competing interests reported.