Developing resources for high-quality applied research investigating the effect of female sex hormones on performance

Female athletes are substantially underrepresented in the sports science literature, with an acute scarcity of studies examining performance outcomes while appropriately controlling for menstrual status. This lack of high-quality research does a disservice to female athletes, as research conducted in men cannot be directly applied to women without consideration of sexual dimorphisms. As such, a correction of the sex- and gender-biases in the sport and exercise science (SES) literature is of primary importance. This thesis addresses dual aims: examining a range of methodologies and menstrual statuses to develop resources that support researchers in conducting high-quality applied SES research in female athletes, alongside examining the potential influence of ovarian hormones on performance.

Study 1 (chapter 3) examined sex differences in the responses to 24-hour manipulations in energy availability (EA) on substrate oxidation, metabolism, and performance, among 20 cyclists/triathletes [10 females using combined monophasic oral contraceptive pills (OCP) and 10 males]. Five different conditions of EA were implemented through a randomised control trial (RCT) in a Latin square design: low/high/higher EA (LEA/HEA/GEA) at 15/45/75 kcal·kg-1 FFM·day-1. Conditions of LEA and HEA were separately achieved by manipulations of either energy intake (EI) or exercise energy expenditure (EEE). The following day fasted peak fat oxidation (PFO) during cycling and two-hour postprandial metabolism were assessed, alongside several physical and cognitive performance tests. Among both sexes, the highest PFO occurred under LEA induced by exercise (p<0.01), while postprandial glucose (p<0.01) and insulin (p<0.05) responses were highest when LEA was induced by diet. Performance during a Wingate test, countermovement jump (CMJ), isometric mid-thigh pull (IMTP), and Stroop Test, did not differ with altered EA (p>0.05). Lastly, the response to EA manipulations did not differ between the sexes across any outcome measure.

Study 2 (chapter 4) employed an observational study design in a training camp environment. National Rugby League Indigenous Women’s Academy athletes [n=11 naturally menstruating (NM), n=13 using HC] completed performance tests [CMJ, squat jump (SJ), IMTP, 20 m sprint, power pass and Stroop Test] during phases 1,2 and 4 of a single menstrual cycle (MC), or during three weeks of hormonal contraceptive (HC) use. Menstrual status was confirmed through ovulation tests alongside serum oestrogen and progesterone concentrations. MC phase or HC use did not influence jump height, peak force, sprint time, distance thrown or the Stroop effect. However, there were small variations in kinetic and kinematic CMJ/SJ outputs. NM athletes produced greater mean concentric power in MC phase 4 than 1 [+0.41 W·kg-1 (+16.8%), p=0.021] during the CMJ, alongside greater impulse at 50 ms at MC phase 1 than 4 [+1.7 N·s (+4.7%), p=0.031] during the SJ, without differences between tests for HC users.

Study 3 (chapter 5) presents a novel observational study design among 37 cyclists/triathletes not using HC. Participants completed four separate virtual e-cycling races [19.5 km time trial (TT)] across a one-month period. At each race, individual hormonal concentrations were correlated to race completion time, with no relationships observed between either 17-β-oestradiol (r=-0.001, p=0.992) nor progesterone (r=-0.023, p=0.833) and TT time. Perceived negative symptoms at each race were also recorded. The total number of MC symptoms was positively correlated to a slower TT time [r=0.268 (95% CI 0.056 to 0.457), p=0.014], as was the number of GI symptoms of at least “moderate” severity pre-race (r=0.233 [95% CI 0.021 to 0.425], p=0.031), but not post-race (r=0.022, p=0.841).

Study 4 (chapter 6) collates the experiences of the female athletes (n=70) participating in all three studies (plus an additional 19 elite athletes), to inform future research and increase female participation rates. The majority (81%) had never participated in research before, with a perceived lack of opportunities as the primary barrier (93%). Participants rated an interest in the research outcome as the most important aspect influencing their decision to participate, followed by receiving personalised results and education. Most participants (87%) stated that they would apply the study findings to their sports involvement, and the majority (94%) indicated a willingness to participate in future studies. The research experience was also rated positively at a mean 77 out of 100.

This series of research studies has contributed numerous novel findings to the literature regarding the influence of the female sex hormones on athletic performance, alongside exploring the nuances of female research participation. Collectively, the findings of this thesis can be summarised as follows:

(1) The responses to acute (24 h), severe, LEA did not differ between sexes. Exercise-induced LEA influenced fasted substrate oxidation more than diet-induced LEA, while LEA did not impair strength/power, sprint capacity, or cognitive performance and so could be implemented by both male and female athletes in the immediate 24 h prior to competition. Future research may consider if sex differences in these responses might be observed across longer LEA time periods, or at a higher EA (less severe LEA dose), alongside examining the influence of fluctuations in oestrogen and progesterone on these findings by focussing on women not using HC.

(2) Performance across tests of explosive power and strength do not differ across a MC, or during active HC use. As such, evidence is currently insufficient to justify “menstrual phase- or status‐based” testing programs at a group to team-based level. There were small variations in kinetic and kinematic CMJ/SJ outputs in NM athletes, without differences between tests for HC users. However, it could not be determined if the observed alterations exceeded between-day variability. Further research is therefore required to fully understand the effects of oestradiol and progesterone on performance, alongside examining MC phases 2 and 3 which
were not captured in this study.

(3) Fluctuations in oestrogen and progesterone concentrations across a MC do not appear to affect real-world cycling performance, while perceived negative MC and GI symptoms may
relate to impaired performance. Therefore, it may be important to focus on the management of negative symptoms to mitigate performance decline. However, a standardised and validated questionnaire to assess the incidence and severity of MC-related symptoms does not currently exist and hence its development should be a priority. Further investigation is also required to understand if specific symptoms are driving an association with performance, and if this relationship persists into other activities beyond cycling.

(4) Female athletes are willing and interested in research participation, but the vast majority (93%) perceive a lack of opportunity as the main barrier to do so. The main motivations for female athletes to participate were an interest in the research outcomes and to receive personalised results. As such, it may be prudent to focus future recruitment efforts on emphasising these study aspects.

Overall, these outcomes demonstrate a lack of association between ovarian hormone fluctuations, either across a MC or with HC use, and the performance measures assessed, either in the laboratory setting as observed during Study 2 or a real-world race as measured during Study 3. As such, an individualised approach to MC monitoring/tracking, with a focus on individual reported symptoms, is likely to represent the current best-practice approach for athletes given the lack of consistent response at the group level. Meanwhile, the overarching aim of this thesis was to examine the practicalities of implementing high quality classification and control of menstrual status in the applied research setting. A range of resources have been developed to aid this pursuit, whilst the methodological decisions and practical learnings from each of the experimental studies are detailed to inform future high-quality research and ultimately facilitate a correction of the sex-bias in SES research

This work © 2025 by Eleanor Smith is licensed under Creative Commons Attribution 4.0 International (https://creativecommons.org/licenses/by/4.0/).