Myths and methodologies: Optimising experimental rigour in heat adaptation research: Menstrual status classification and scheduling approaches

Women remain underrepresented in thermal physiology research, particularly within studies examining physiological adaptation to hot environments. Among the limited research that includes female participants, few studies have appropriately classified menstrual status of their participants or rigorously accounted for ovarian hormone influences. Both endogenous and exogenous ovarian hormones have been demonstrated to influence thermoregulatory responses. Failing to control for these factors can confound interpretation; observed adaptations may reflect hormonal variation rather than true physiological adaptation. This methodological review offers guidance on incorporating ovarian hormone considerations into mechanistic heat adaptation studies, emphasising the highest standards of research rigour. We recognise applied research and real-world implementation may necessitate greater methodological flexibility. Part 1 presents a three-tiered approach (bronze-to-gold tier) to accurately classify menstrual status in female participants, enabling scalable implementation from low-cost, low-burden methods to higher-resource, high-rigour approaches. Part 2 offers guidance for experimental scheduling, including the potential benefits of standardising testing within defined menstrual phases, to minimise the confounding effects of endogenous and exogenous ovarian hormones. Crucially, given biological variability, this section also highlights the importance of transparent, detailed and consistent documentation of the testing timing relative to participants menstrual cycle or hormonal contraceptive use, regardless of approach, to enhance interpretation and reproducibility. By highlighting key methodological considerations, this review aims to promote methodological consistency and enhance the rigour of studies including women in heat adaptation research. Implementing these recommendations will support more valid comparisons across studies, facilitate meta-analyses and ultimately contribute to the development of evidence-based heat adaptation guidance for women.