No clear influence of menstrual cycle phase or hormonal contraceptive use on heat acclimation adaptations: A systematic review and meta-analysis

Heat acclimation (HA) involves repeated heat exposures that induce physiological adaptations to improve heat tolerance and performance. However, female-specific physiological factors, including endogenous and exogenous hormonal fluctuations, are rarely considered in HA research. This study examined whether menstrual cycle phase and hormonal contraceptive use influence the magnitude of heat adaptation and evaluated the effectiveness of HA protocols in females. PubMed and SPORTDiscus were searched in March 2025 and April 2026. Pre- and post-HA mean ± SD values for relevant outcomes were extracted to calculate Hedges’ g effect sizes with 95% confidence intervals. Random-effects models were used to estimate pooled effects. Studies were categorized by menstrual cycle phase (follicular and luteal), hormonal status (naturally menstruating and hormonal contraceptive users), reporting type (pooled or separate phases), and HA protocol type (isothermal or fixed work rate). Seven studies were included. Most assessed HA within a single menstrual phase; therefore, findings primarily represent between-subject responses rather than direct comparisons of hormonal effects. No consistent differences were observed between menstrual cycle phases or hormonal contraceptive users. HA protocol type influenced only the exercising heart rate, with fixed-work-rate protocols producing greater reductions than isothermal protocols. Current evidence does not demonstrate a clear influence of menstrual cycle phase or hormonal contraceptive use on physiological adaptations to HA. Adaptations appear to be more strongly influenced by HA protocol characteristics. However, conclusions remain limited by small sample sizes, inconsistent menstrual cycle verification, and the predominance of between-subject study designs, highlighting the need for well-controlled longitudinal research in females.