What is the topic of this review? This review integrates a methodological audit of passive heat intervention (PHI) studies with a systematic review of physiological, perceptual, and performance markers of heat adaptation. Focus is placed on participant representation, menstrual status reporting, and how sex-specific considerations are incorporated into study design. What advances does it highlight? This review identifies opportunities to strengthen PHI research through improved female inclusion and clearer participant characterisation. It also consolidates evidence that PHI can elicit meaningful heat adaptation, supporting more inclusive and population-relevant approaches for maintaining health and wellbeing during heat exposure. Background: Passive heat interventions (PHI) 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, female participant representation within this literature remains unclear. This study integrated an audit of PHI research with a systematic review of selected heat-adaptation phenotypes to characterise current practices and identify methodological gaps. Methods: Using a standardised framework (Smith et al., 2022), searches of PubMed, Web of Science, ScienceDirect, SPORT Discus and Scopus were conducted. Included studies implemented PHI (≥3 days) and reported markers of heat adaptation. Results: Seventy-three studies (1,392 participants; 427 females) met inclusion criteria. Six studies recruited female-only participants, four conducted sex-based sub-analyses, and none were 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 Smith et al., (2022) 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 to –0.5°C), skin temperature (–0.4 to 0.1°C), heart rate (–2 to –11 b·min⁻¹), blood pressure (–2 to –5 mmHg), plasma volume (–1 to 22%) and sweat rate (0.1 to 0.4 L.h-1). Conclusion: PHI research is characterised by female underrepresentation and limited menstrual-status reporting, constraining confidence in how evidence reflect the broader population. Although PHI can modify heat-adaptation phenotype, these responses are derived largely from male participants. Sex-informed trials are needed to strengthen mechanistic understanding and translational application.
Mee et al. (Tue,) studied this question.