The core temperature of females follows a rhythm set by fluctuating reproductive hormones across the menstrual cycle. The onset and effectiveness of heat loss pathways have also been shown to reflect these changes observed in core temperature. Research suggests that female athletes competing in hot ambient conditions may experience a more severe performance impairment in the later-half of their menstrual cycle due to this unique relationship between the concentration of hormones, core temperature and heat loss mechanisms. Despite more female athletes competing for podium positions than in any previous decade and a pressing need for female-specific evidence, our current knowledge surrounding the female reproductive system and its influences on thermoregulatory responses is limited. Much of the available research reports conflicting or inconclusive results or are limited by the complex methodological complications associated with fluctuating female hormones. The first investigation (Chapter 3) aimed to quantify the representation of female participants in exercise thermoregulation research over the past decade to offer perspective on the volume of novel literature directly applicable to female populations. This was conducted through a review of original exercise thermoregulatory studies published in three major Sports Medicine databases (PubMed, Medline and SPORTDiscus) between 2010 and 2019. Articles were screened to determine the number of female and/or male participants in the study. The review highlights the underrepresentation of female participants in the exercise thermoregulation literature over the past decade. Rather than studied independently, females have been typically studied alongside males, yet remain underrepresented, with the median sample size of female and male subgroups found to be six and 10, respectively. While there was an improvement in the proportion of females in the literature between 2010 and 2019, this was explained by a reduction in the proportion of studies with only males, rather than an increase in the recruitment of females. To improve the quality of future investigations and facilitate increased knowledge in female exercise thermoregulation research, methodological consistency, multi-phase testing and appropriate study planning, design and analysis are recommended. This being said, despite our own efforts to plan, design and analyse the subsequent experimental study as per these recommendations, we too experienced firsthand the challenges of studying female cohorts and were limited by a small sample size (n = 6). While further investigation on the overall topic of female thermoregulation is required, of considerable interest is the potential effects of the menstrual cycle on autonomic and behavioural heat loss responses and subsequently performance while in hot conditions. Given the increasing number of females involved in women`s professional sport, building a more comprehensive understanding of how hormonal shifts alter performance in thermally challenging environments would be of substantial benefit. Hence, the second study (Chapter 4) was conducted to examine the effect of hormonal variations on cycling performance and pacing in hot, humid conditions. Eight trained eumenorrheic cyclists completed two self-paced time trials in simulated hot, humid conditions (31.0 °C, 58% relative humidity). Trials were conducted in the early-follicular (EF) and mid-luteal (ML) phases of the menstrual cycle. The 22.1 km undulating course replicated the women`s individual road cycling time trial event at the Tokyo 2021 Olympic Games. The environmental conditions were also equivalent to the mean peak temperature expected for the Tokyo Games. Data from six participants were included in the analysis. The key findings of the study were: 1) completion time was not statistically different, and not statistically equivalent, between the phases (E = -66.3 seconds; p = .24); 2) rectal temperature was statistically higher in the ML phase than in the EF phase, at baseline (E = 0.28 °C; p = .59) and throughout the time trial (E = 0.32 °C; p = <.001); and 3) power output during the time trial was not statistically different between phases (E = -8.37 watts; p = .20), indicating pacing behaviour was similar between the phases. Thus, the original hypothesis, that performance would be impaired in the ML phase due to the high core temperature observed in this phase, was not supported. However, as the results neither support that performance was different or support that performance was the same between the menstrual phases, the results do not negate that performance is influenced by the menstrual cycle and thus remain inconclusive. In summary, the findings of this thesis have highlighted the underrepresentation of females in modern exercise thermophysiology research. The review provided an account of the challenges of testing females, especially with regards to the menstrual cycle, but also justified the need for further research to improve knowledge and inform evidence-based practice that is relevant to female populations. The findings from the experimental study, albeit limited by the small sample size, were not conclusive and as such were unable to confirm or refute the original hypothesis. The variability seen in performance outcomes has prompted questions on whether alterations in performance regulated by progesterone and oestrogen may not occur uniformly within menstrual phases. The inconsistent reproductive hormone concentrations within and between individuals is a possible cause of this variability.
© Copyright 2020 Veröffentlicht von Queensland University of Technology. Alle Rechte vorbehalten.