Passive heat intervention research in women: systematic review and audit of female representation

Passive heat interventions (PHIs) are non‐exercise heat‐acclimation strategies that improve physiological markers associated with heat tolerance and reduce vulnerability to heat‐related illness, when exercise is not feasible. However, representation of female participants within this literature remains unclear. In this study, we integrated an audit of PHI research with a systematic review of selected heat‐adaptation phenotypes to characterize current practices and identify methodological gaps. Using a standardized framework, searches of PubMed, Web of Science, ScienceDirect, SPORT Discus and Scopus were conducted. Included studies implemented PHIs (≥3 days) and reported markers of heat adaptation. Seventy‐three studies (1392 participants; 427 females) met inclusion criteria. Six studies recruited only female participants, four conducted sex‐based subanalyses, and none was designed to examine sex differences. No study achieved gold classification menstrual status reporting, with most classified as ungraded (n = 16) or unclassified (n = 22), using the standardized framework. Participants were predominantly sedentary, recreationally active or trained, with ∼49% representing clinical populations. The systematic review showed PHI‐associated heat‐adaptation outcomes, including changes in core temperature (0.0°C to −0.5°C), skin temperature (−0.4°C to 0.1°C), heart rate (−2 to −11 beats min−1), blood pressure (−2 to −5 mmHg), plasma volume (−1% to 22%) and sweat rate (0.1 to 0.4 L h−1). PHI research is characterized by female underrepresentation and limited menstrual status reporting, constraining confidence in how evidence reflects the broader population. Although PHIs can modify the heat‐adaptation phenotype, these responses are derived largely from male participants. Sex‐informed trials are needed to strengthen mechanistic understanding and translational application.