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

Abstract

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.