The impact of body fat on thermoregulation during exercise in the heat: A systematic review and meta-analysis

Objectives We performed a systematic review and meta-analysis to examine the effect of body fat on thermoregulatory responses to exercise in the heat. Design Systematic Review and Meta-analysis. Methods We systematically searched databases (N = 8) for studies that included: healthy participants; an aerobic exercise intervention under heat stress; a measure of body fat by a high and low body fat group; pre- and post-exercise internal temperature, and/or post-exercise mean skin temperature and whole body sweat loss. Criteria to distinguish high body fat and low body fat were determined by each qualifying study. Out of 1222 potential studies, 10 qualified. Robust variance estimation models were utilized to determine the pooled effect size (ES, 95% CI) for interventions that performed unbias comparisons between groups. Results Participants (n = 211) were mostly male (70%) and young (19.3 ± 7.1 years) with a maximal oxygen consumption of 50.42 ± 9.3 ml∙kg-1∙min-1 by high body fat (36.7 ± 11.8%) and low body fat (17.8 ± 5.7%). Exercise duration was between 30 and 60 min at moderate-high intensity (44.1-71.4% VO2max) at 28-40.3 °C and 26-50% humidity. Of the 7 interventions that normalized metabolic heat production to body mass and 5 interventions that normalized to external workload, there were no differences in any of the three outcome variables between groups. Conclusions Many of the included studies did not control for confounding factors that may affect the relationship between body fat and thermoregulation during exercise in the heat such as metabolic heat production and body mass. Given the small number of interventions included, future work must make unbiased comparisons to appropriately assess the independent influence of body fat.