Abstract
end to outperform female athletes in several endurance sports. Maximum cardiac output can be estimated by maximal oxygen consumption ( VO2max ), and it has been estab- lished that men present VO2max values about 20% higher than women. Although sex differences in VO2max have already been well studied, few studies have assessed sex differences with regard to muscle oxidative capacity. The aim of this study was to compare aerobic muscle quality, accessed by VO2max and adjusted by lower limb lean mass, between male
it has been estab- lished that men present VO2max values about 20% higher than women. Although sex differences in VO2max have already been well studied, few studies have assessed sex differences with regard to muscle oxidative capacity. The aim of this study was to compare aerobic muscle quality, accessed by VO2max and adjusted by lower limb lean mass, between male and female amateur triathletes. The study also aimed to compare sex differences according to VO2submaximal values assessed at ventilatory thresholds. A total of 57 participants (23 women and 34 men), who had been training for Olympic-distance triathlon races, underwent body composition evaluation by dual-energy X-ray absorptiometry and performed a cardiorespiratory maximal test on a treadmill. Male athletes had signi cantly higher VO2max, both absolutely and when adjusted to body mass. Conversely, when VO2max was adjusted for lean mass, there was no signi cant difference between sexes. The same was observed at submaximal exercise intensities. In conclusion, differences in VO2max adjusted to body mass but not lean mass may explain, at least in part, sex differences in performance in triathlons, marathons, cycling, and other endurance sports. Keywords:ventilatory threshold; VO2max; triathlon; respiratory compensation point; women 1. Introduction Triathlon is an endurance sport that consists of a sequential swim, cycle, and run over a variety of possible race distances, from the sprint triathlon (750 m swimming, 20 km cycling, and 5 km running) to ironman distance (3800 m swimming, 180 km cycling, and 42 kmrunning) [1]. In this sport, good performance relies on the ability to sustain a high rate of energy expenditure for prolonged periods, which fundamentally depends on the ability to resynthesize ATP via aerobic metabolism [2]. It is well known that male athletes present better aerobic performance than female athletes in several endurance sports, such as swimming [36], cycling [7,8], running [9], and triathlon races over different distances [10,11]. However, with the increase in women's Healthcare2023,11, 1502.
Healthcare2023,11, 1502 2 of 9 participation in amateur and elite long-distance sports during the last three decades, the sex differences in performance seem to be decreasing [12,13]. This seems to be associated with improvements in women's performance over the last few decades [1416]. Among the determinant factors of successful aerobic metabolism and consequently long-distance event performance, is the maximal capacity to uptake, transport, and utilize oxygen, which is called maximal oxygen consumption ( VO2max ) [17]. VO2max is measured in liters per minute (L/min); therefore, this measurement re ects the maximum amount of oxygen that an individual is capable of consuming per unit of time. However, to be able to compare individuals of different body mass, VO2max is also expressed as a body mass-adjusted rate (mL/min/kg) [18,19]. VO2max is determined by the product of maximal cardiac output and the maximal arterio-venousO2content difference, VO2= Q (a ¯v O2diff) [20]. Although VO2max could be limited by either of these factors, it is accepted that in the exercising human, it is limited by the cardiovascular ability to deliver oxygen, in other words, by maximum cardiac output [17,21], and not by skeletal muscle O2extraction [17]. In this context, there is also a consensus in the literature that female athletes exhibit relatively lower VO2max (mL/min/kg) values than males when cycling orrunning [10,11] . This has often been attributed to central factors, such as a smaller heart and lower hemoglobin mass in females, limiting women's capacity to deliver oxygen to skeletal muscle [20,22]. Overall, VO2maxvalues are approximately 20% lower in women than in men [23]. Although the male advantage in long distance events has been attributed to the sex difference in VO2max [24], the degree of difference in triathlon performance between women and men seems to be smaller than the difference in VO2max . The current estimate is that women are approximately 12%18% slower than men, depending on the level of competition and triathlon distance [12,13]. Therefore, other physiological factors seem to affect performance signi cantly. The ability of skeletal muscle to extract oxygen does not affect VO2max but is critical to determining the percent of
be smaller than the difference in VO2max . The current estimate is that women are approximately 12%18% slower than men, depending on the level of competition and triathlon distance [12,13]. Therefore, other physiological factors seem to affect performance signi cantly. The ability of skeletal muscle to extract oxygen does not affect VO2max but is critical to determining the percent of VO2max that can be maintained during exercise [17]. In this context, sex differences in performance arising from large differences in VO2max could be mitigated if females are able to maintain a higher percentage of their VO2max for long periods of time [10]. However, sex differences related to the ability of skeletal muscle to extract oxygen are much less studied than cardiac or pulmonary factors. An interesting variable from which more could be inferred about this aerobic muscle quality is VO2max adjusted by skeletal muscle mass [25,26]. This variable is less studied than non-adjusted VO2max (L/min or mL/min/kg), possibly because it is dif cult to adequately assess. Lean mass can be reliably determined by magnetic resonance imaging or dual-energy X-ray absorptiometry (DXA), but the necessary equipment is not very accessible due to its high cost. To the best of our knowledge, there are few scienti c reports comparing aerobic muscle quality between sexes, as assessed by VO2max adjusted by lean mass. Those that do exist show controversial results, probably resulting from the different methodologies and different participant characteristics [27]. Therefore, the aim of the present study was to compare aerobic muscle quality, assessed by VO2max adjusted by lower limb lean mass, between male and female amateur triathletes. The study also aimed to compare sex differences in VO2submaximal values assessed at ventilatory thresholds. Moreover, the study aimed to compare male and female triathletes according to their body composition. We hypothesized that the sex differences in absolute and body mass-adjusted VO2max is higher than the sex difference in lean mass-adjusted VO2max. 2. Materials and Methods 2.1. Ethical Approval All experimental procedures were approved by the Human Research Ethics Commit- tee of Federal University of São Paulo (approval number 0973/2021) and conformed to the
triathletes according to their body composition. We hypothesized that the sex differences in absolute and body mass-adjusted VO2max is higher than the sex difference in lean mass-adjusted VO2max. 2. Materials and Methods 2.1. Ethical Approval All experimental procedures were approved by the Human Research Ethics Commit- tee of Federal University of São Paulo (approval number 0973/2021) and conformed to the
Healthcare2023,11, 1502 3 of 9 principles outlined in the Declaration of Helsinki. All participants voluntarily gave their informed consent to participate in the study after receiving instructions about the experi- mental procedures, their possible risks and bene ts, and a guarantee of anonymity rights. 2.2. Participants Fifty-seven amateur triathletes (23 women and 34 men) who had been training for Olympic-distance triathlon races (1500 m swim, 40 km cycle, and 10 km run) participated in the study. Participant recruitment was carried out through social networks and direct contact with trainers and sports consultants. The inclusion criteria to participate in the study included having participated in at least one Olympic-distance triathlon race with at least one year of triathlon training. The exclusion criteria included having no medical approval for maximal effort testing, pregnancy, acute pain in the lower limbs, edema, and taking any medicine known to affect physical performance, such as anabolic steroids, betablockers, and antidepressants. The descriptive characteristics of the participants are presented in Table. There was no signi cant difference in age between male and female athletes who participated in the study. Table 1.Characteristics of the participants.Women (n = 23) Men (n = 34) p-Value Effect Size (d) CI for Effect Size Power Age (years) 42.0 7.3 38.9 6.9 0.106 0.44 0.01 to 0.89 0.486 BM (kg) 58.1 6.6 74.9 9.1 <0.001 1.94 1.00 to 2.90 1.000 Height (cm) 163.7 5.7 175.4 6.7 <0.001 1.85 0.96 to 2.70 0.999 Values are expressed as mean SD. Abbreviations: BM = body mass in kg; d = effect size; power = (1 b); CI = con dence interval. 2.3. Study Design After a detailed explanation of the experimental protocol, including risks and bene ts, the participants read and signed the informed consent form. All tests were performed from January to February 2022. Athletes were asked to eat a light meal no later than 2 h prior to the tests and to drink no coffee, tea, or other caffeinated beverages on the day of the laboratory visit. All tests were performed in the morning to avoid circadian rhythm in uences. All participants attended the
All tests were performed from January to February 2022. Athletes were asked to eat a light meal no later than 2 h prior to the tests and to drink no coffee, tea, or other caffeinated beverages on the day of the laboratory visit. All tests were performed in the morning to avoid circadian rhythm in uences. All participants attended the laboratory for 1 day, during which they answered a questionnaire about their training routine, were submitted to anthropometric and body composition measurements, and underwent a cardiorespiratory maximal test on a treadmill. 2.4. Assessments 2.4.1. Questionaries The questionnaire included four open questions about the participants training habits: How many hours per week do you train by cycling? How many hours per week do you train by running? How many hours per week do you train by swimming? How long have you been doing triathlon training? 2.4.2. Body Composition and Anthropometry Body composition was assessed by DXA (Lunar DPX, Wisconsin, USA, software version 12.3 ). This method provides a rapid and non-invasive assessment of fat mass (FM) and fat-free mass (FFM) with a minimum radiation dose [28], which is the reference method in clinical research. Skeletal muscle mass was estimated as bone-free lean tissue measured in kilograms [29]. All tests were performed by the same examiner, with the subjects in a supine posi- tion and wearing comfortable clothes without metal pieces, centrally aligned with 10 cm between the feet and 5 cm between the hands and trunk.
Healthcare2023,11, 1502 4 of 9 2.4.3. Cardiorespiratory Incremental Maximal Test on a Treadmil All participants performed a cardiorespiratory maximal test on a treadmill (Inbrasport, ATL, Porto Alegre, Brazil) to identify VO2max, ventilatory threshold (VT), respiratory compensation point (RCP), and maximal aerobic speed (MAS) using a computer-based metabolic analyzer (Quark, Cosmed, Italy). Before each test, volume and gas calibration were completed according to the manufacturer's guidelines. The test began with a four- minute warm-up period at 9 km/h for women and 10 km/h for men; speed was then increased at a rate of 1 km/h every minute until exhaustion [30]. A 1% grade was main- tained during the entire test to simulate the energetic cost of outdoor running [31]. The entire test lasted 812 min for all participants. The heart rate was recorded throughout the test by a monitor (Ambit 2S, Suunto, Finland). Perceived exertion was reported by the participant at the end of each treadmill speed interval and rated using the Borg scale [32]. Expired gases were measured breath-by-breath, and all measured data were averaged over 20 seconds for analysis. VO2max was identi ed as a VO2plateau, i.e., an increase in VO2of less than 2.1 mL/kg/min between two or more consecutive speed stages, and all participants met this criterion by the end of the test. VO2max was measured in absolute values (L/min), and VO2max adjusted for total body mass (mL/min/kgBM) and lower limb lean mass (mL/min/kgLM) was calculated [33]. MAS was de ned as the minimum speed required to elicit VO2max during the cardiorespiratory incremental maximaltest [34] . VT was determined by the in ection in the ventilation curve, representing an increase in the ventilatory equivalent for oxygen without an increase in the ventilatory equivalent for carbon dioxide and an increase in the partial pressure of exhaled oxygen with no change in the partial pressure of exhaled carbon dioxide. RCP was determined by the in ection in the ventilation curve, representing an increase in the ventilatory equivalent for oxygen and the ventilatory equivalent for carbon dioxide and an increase in the partial pressure of exhaled oxygen with a decrease in
increase in the partial pressure of exhaled oxygen with no change in the partial pressure of exhaled carbon dioxide. RCP was determined by the in ection in the ventilation curve, representing an increase in the ventilatory equivalent for oxygen and the ventilatory equivalent for carbon dioxide and an increase in the partial pressure of exhaled oxygen with a decrease in the partial pressure of exhaled carbon dioxide [35]. Two experienced investigators identi ed the VT and RCP, but in case of discordance, a third investigator was asked. 2.5. Statistical Analysis The data were presented as means with standard deviations. All variables presented a normal distribution and homogeneous variability according to the Shapiro-Wilk test and Levene's test, respectively. Student's t-test was used to compare mean values between male and female participants. SPSS version 21.0 (SPSS, Inc., Chicago, IL, USA) was used to perform the analysis. G*Power version 3.1.9.2 (Franz, Universität Kiel, Germany) was used to determine the sample size and analyze the test power level. A sample size calculation on the VO2max adjusted by lean mass using data from a pilot study (n = 10) showed that fty athletes (twenty- ve of each sex) were needed to detect a relevant difference with 80% power and a signi cance level of 5%. Lean mass- adjusted VO2max in this pilot study was200 5mL/min/kgLM for male athletes and 192 15mL/min/kgLM for female athletes. For power level calculation, at-test family was selected, and mean values, standard deviations, and effect sizes (Cohen's d) were included in the calculation. The measure of the effect size for differences between sexes was determined by calculating the mean difference between the two sexes, then dividing the result by the pooled standard deviation. The magnitude of effect sizes was judged;d<0.2 was considered no effect,0.2 d< 0.5was considered a small effect size,0.5 d< 0.8 represented a medium effect size, andd 0.8was considered a large effect size [36]. The level of signi cance was set atp<0.05. 3. Results With regards to swimming, cycling, and running training hours per week, male and female athletes did not differ signi cantly (Table).
considered no effect,0.2 d< 0.5was considered a small effect size,0.5 d< 0.8 represented a medium effect size, andd 0.8was considered a large effect size [36]. The level of signi cance was set atp<0.05. 3. Results With regards to swimming, cycling, and running training hours per week, male and female athletes did not differ signi cantly (Table).
Healthcare2023,11, 1502 5 of 9 Table 2.Triathlon training hours per week. Women (n = 23) Men (n = 34) p-Value Effect Size (d) CI for Effect Size Power Swimming (hours/week) 3.3 1.3 3.0 1.1 0.319 0.271 0.19 to 0.73 0.257 Cycling (hours/week) 5.8 1.2 5.0 1.7 0.058 0.522 0.07 to 0.98 0.604 Running (hours/week) 4.0 1.0 3.7 1.1 0.269 0.301 0.15 to 0.75 0.293 Values are expressed as mean SD. Abbreviations: power = (1 b); d = effect size; CI = con dence interval. The absolute VO2max, body mass-adjusted VO2max, lean mass-adjusted VO2max, and speed reached at maximal intensity and ventilatory thresholds are presented in (Table). Comparing the maximal values, absolute (L/min) and body mass-adjusted (mL/min/kgBM) VO2max values than the female group. Regarding MAS, the male athletes also reached higher speeds than the female athletes (Table). Conversely, when the VO2max values were adjusted for lean mass (mL/min/kgLM), there was no signi cant difference between sexes (Table). Comparing the values reached at ventilatory thresholds, strated signi cantly higher values than female athletes for absolute and body mass-adjusted VO2at submaximal exercise intensities and higher speeds measured at VT and RCP. How- ever, VO2adjusted for lower limb lean mass was not signi cantly different between sexes in both VT and RCP). Fat mass (%) and lean mass (kg) were also presented in (Table). Male athletes presented higher lean mass and lower fat mass than the female athletes. Table 3.Descriptive characteristics of the participants. Women (n = 23) Men (n = 34) p-Value Effect Size (d) CI for Effect Size Power Maximal exercise intensity VO2max(L min 1 ) 2.97 0.35 4.42 0.50 <0.001 3.240 1.7 to 4.8 0.999 VO2max(mL min 1 kgBM 1 ) 50.86 6.93 59.67 5.81 <0.001 1.403 0.7 to 2.1 0.999 VO2max(mL min 1 kgLM 1 ) 188.70 18.75 194.66 17.24 0.222 0.333 0.1 to 0.8 0.332 MAS (km h 1 ) 15.04 1.74 17.88 1.45 <0.001 1.802 0.6 to 4.2 0.999 Submaximal exercise intensityVT VO2(L min 1 ) 2.28 0.36 3.29 0.38 <0.001 2.670 1.4 to 3.9 0.999 VT VO2(mL min 1 kgBM 1 ) 39.40 6.17 44.59 4.80 <0.001
VO2max(mL min 1 kgLM 1 ) 188.70 18.75 194.66 17.24 0.222 0.333 0.1 to 0.8 0.332 MAS (km h 1 ) 15.04 1.74 17.88 1.45 <0.001 1.802 0.6 to 4.2 0.999 Submaximal exercise intensityVT VO2(L min 1 ) 2.28 0.36 3.29 0.38 <0.001 2.670 1.4 to 3.9 0.999 VT VO2(mL min 1 kgBM 1 ) 39.40 6.17 44.59 4.80 <0.001 0.963 0.3 to 2.1 0.963 VT VO2(mL min 1 kgLM 1 ) 145.73 16.15 145.61 13.01 0.975 0.008 0.1 to 0.1 0.053 VT speed (km h 1 ) 10.78 1.51 12.44 1.40 <0.001 1.150 0.7 to 1.6 0.994 Submaximal exercise intensityRCP VO2(L min 1 ) 2.68 0.36 3.85 0.43 <0.001 2.87 1.5 to 4.2 0.999 RCP VO2(mL min 1 kgBM 1 ) 46.24 6.33 52.34 5.96 <0.001 0.997 0.6 to 1.4 0.976 RCP VO2(mL min 1 kgLM 1 ) 171.28 16.34 170.72 15.14 0.894 0.036 0.4 to 0.4 0.064 Speed RCP (km h 1 ) 12.78 1.48 14.82 1.49 <0.001 1.376 0.8 to 1.8 0.999 Body composition Lean mass (kg) 43.1 5.4 59.2 6.0 <0.001 2.778 1.4 to 4.1 0.999 Fat mass (%) 21.9 8.6 16.2 5.3 0.003 0.843 0.4 to 1.3 0.949 Values are expressed as mean SD. Power = (1 b); VO2max = maximal oxygen uptake; BM = body mass; LM = lean mass of lower limbs;MAS = Maximum aerobic speed; VT = ventilatory threshold; RCP = respira- tory compensation point. 4. Discussion It is well known that VO2max are higher in male athletes than in female athletes, and this is thought to drive the sex difference in endurance sport performance. However, there is no consensus on sex differences regarding muscular aerobic capacity. Therefore, the main aim of the present study was to compare the aerobic muscle capacity, assessed by VO2max adjusted to lower limb lean mass rather than absolute or body mass-adjusted VO2max, between male and female triathletes. The main ndings of the present study were (i) adjusted to lower limb lean mass, VO2max was no different between sexes; (ii) absolute and body mass-adjusted VO2max
Description
This study compares aerobic muscle quality between male and female amateur triathletes.