ECSS Paris 2023: CP-PN18
INTRODUCTION: Cardiac autonomic regulation, commonly indexed by heart rate variability (HRV), is frequently hypothesized to fluctuate systematically across the menstrual cycle. Empirical findings, however, remain inconsistent, likely due to sparse phase-based sampling and limited consideration of interindividual variability. The aim was to examine cyclic HRV trajectories employing dense longitudinal monitoring and phase-aligned cycle time scaling (PACTS) to distinguish population-level from individual-specific patterns and to evaluate the role of daily subjective well-being. METHODS: Daily HRV using smartphone photoplethysmography and well-being data were collected across and up to four menstrual cycles in 21 naturally cycling women. Cycle time was aligned using PACTS, with ovulation set to 0 and follicular and luteal phases rescaled to a common −1 to +1 interval. Short-term HRV was indexed using vagally-mediated log-transformed RMSSD, and coefficient of variation (CV) of ln(RMSSD), computed from a centered 3-day rolling window. Non-linear cyclic trajectories were analyzed using cyclic generalized additive mixed models (GAMMs), separating population-level smooths from participant-specific cyclic deviations. Associations between daily well-being (sleep, stress, fatigue, pain) and HRV were examined using linear mixed-effects models distinguishing within-person from between-person effects. RESULTS: For ln(RMSSD) (n=1213), the population-level cyclic smooth over PACTS time was flat and non-significant (s(t_pacts): edf≈0, p=0.483), whereas participant-specific cyclic deviations were significant (ti(t_pacts, ID): edf=20.47, p=0.013), indicating pronounced interindividual heterogeneity despite a stable average trajectory (adjusted R²=0.443). Comparable results were observed for CV ln(RMSSD) (n=1110), with no significant population-level cyclic pattern (edf=0.007, p=0.067) but strong individual-specific cyclic variability (edf=54.52, p<0.001; adjusted R²=0.349). Within-person analyses showed that worse daily sleep, higher stress, and greater fatigue were associated with lower ln(RMSSD) (all p≤0.003), whereas between-person differences were not related to mean ln(RMSSD). Further, within-person increases in stress and pain were associated with modest increases in CV ln(RMSSD) (both p=0.030). CONCLUSION: When menstrual cycle timing is precisely aligned to ovulation, vagally-mediated HRV does not exhibit a consistent population-level rhythm. Instead, HRV dynamics are highly individual and strongly modulated by day-to-day fluctuations in subjective well-being. Previously reported inconsistencies in menstrual cycle effects on HRV may therefore reflect unmodeled interindividual variability and short-term contextual influences rather than weak or absent physiological effects.
Read CV Marcelle SchaffarczykECSS Paris 2023: CP-PN18
INTRODUCTION: Low energy availability (LEA) has been recognized as a challenge for physically active and athletic individuals [1] as well as military service personnel [2]. LEA is defined as a mismatch between dietary energy intake to cover energy expenditure due to physical activity and/or exercise that results in a decrease in energy availability (EA) for physiological processes that maintain athlete health and support training adaptations [3]. A relatively common sign of LEA in females not using hormonal contraceptives (HC) is hormonal dysfunction manifested as menstrual disturbances that can range from subclinical disturbances such as anovulation or an “inadequate” luteal phase to clinically more concerning oligomenorrhea/amenorrhea, which is recognized as a severe primary indicator/primary indicator of relative energy deficiency in sport (REDs). Several other hormonal indicators of LEA/REDs have been identified including: sub-clinically or clinically low total or free T3, sub-clinically or clinically low IGF-1, and elevated resting or 24-hour urine cortisol [4]. Approximately half of the female athletic population and approximately two-thirds of female military service personnel [5,6] are HC users. HC use may alter hormonal milieu beyond their intended target of reproductive hormones. Importantly, HC users are not immune to problems associated with under-fueling, overtraining, and psychological stress but the hormonal cycles of HC users may be masked rendering this severe primary indicator/ primary indicator of REDs unusable in this population. METHODS: Cross-sectional data from the NoREDS (Athletic Performance and Nutrition) three-year follow-up study, comprising 146 national- to international-level female athletes was analyzed. RESULTS: IGF-1 concentrations were lower in HC users than in naturally menstruating females, cortisol levels were higher in HC users than in in naturally menstruating females, and that triiodothyronine (T3) concentrations were higher in HC users than in naturally menstruating females. CONCLUSION: These results combined with published longitudinal data indicating similar trends and confirmed LEA in naturally menstruating females, combined HC users and progestin-only HC users [7] have led to the hypothesis that HC use and LEA both independently and synergistically alter hormone concentrations. Increasing knowledge regarding the effect of hormonal contraceptives on exercise performance and indicators associated with LEA and REDs is essential. Many women need/desire hormonal contraceptives to support their menstrual health and overall health thus considering this population (and sub-populations) in their research has relevance for sport and exercise, performance and aspects of well-being. 1. Logue et al. (2018) SportsMed. 2. O’Leary et al. (2020) FrontNutr 3. Loucks et al. (2011). JSportsSci. 4. Stellingwerff et al. (2023) BrJSportsMed. 5. Witkop et al. (2017) Contraception. 6. Myers et al. (2024) BMJMilHealth. 7. Mikkonen et al. (2025) EurJSport Sci
Read CV Ritva MikkonenECSS Paris 2023: CP-PN18
INTRODUCTION: Hormonal contraceptives, commonly used by female athletes and servicewomen, contain synthetic oestradiol and/or progestogens that influence endogenous oestradiol and androgens; these hormones have widespread effects on neuromuscular and musculotendon function. This study compared neuromuscular function and musculotendon properties in physically active women using different hormonal contraceptive methods. METHODS: Participants were 66 women (aged 18-38 y) who were naturally menstruating (MC) (n = 20) or using the combined oral contraceptive pill (COCP) (n = 17), a progestogen-only contraceptive (POC) (n = 14), or the intra-uterine system (IUS) (n = 15). Body composition was determined by DXA and current physical activity recorded by questionnaire. Experimental testing was completed at ovulation (confirmed by urinary luteinising hormone) for MC, at the end of the active pill phase (day 21) for COCP, and at a time of convenience for POC and IUS. Fasted circulating concentrations of oestradiol, testosterone, sex hormone binding globulin (SHBG), androstenedione, dehydroepiandrosterone-sulfate (DHEA-S), and insulin-like growth factor-I (IGF-I) were measured. Knee extensor isometric, and knee extensor and flexor isokinetic (60 and 180°·s-1), peak torque were measured using isokinetic dynamometry. Lower limb muscle and tendon stiffness, tone, and elasticity were measured using digital palpation. A one-way ANCOVA compared groups controlling for age, body mass, and physical activity. RESULTS: There were no between-group differences in demographics, body composition, or physical activity. IGF-I and DHEA-S did not differ between groups (p ≥ 0.089). Oestradiol was higher in MC than COCP and POC (p ≤ 0.032) but not different to IUS (p = 0.334). Oestradiol was higher in POC and IUS (p < 0.001) than COCP but POC and IUS were not different (p = 0.334). Testosterone was higher in IUS than COCP (p = 0.005) but was not different between other groups (p ≥ 0.061). SHBG was lower in MC than COCP (p < 0.001) but MC was not different to POC or IUS (p ≥ 0.143). SHBG was higher in COCP than POC and IUS (p < 0.001) but POC and IUS were not different (p = 0.903). Free androgen index was higher in MC and POC than COCP (p < 0.001) but MC and POC were not different (p = 0.435). Free androgen index was higher in IUS than MC and COCP (p ≤ 0.048) but not different between IUS and POC (p = 0.435). Androstenedione was higher in MC than COCP (p < 0.001) but MC was not different to POC or IUS (p ≥ 0.058). Androstenedione was higher in POC and IUS (p ≤ 0.006) than COCP but POC and IUS were not different (p = 0.363). Peak knee extensor torque, peak knee flexor torque, and lower limb musculotendon elasticity, stiffness, and tone did not differ between groups (p ≥ 0.077). CONCLUSION: Hormonal contraceptives may influence circulating androgens, but it is unlikely these androgens exert measurable effects on lean mass, neuromuscular function, or musculotendon properties.
Read CV Erin RobertsonECSS Paris 2023: CP-PN18