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

Abstract

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% VO 2 max) 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.Published by Elsevier Ltd on behalf of Sports Medicine Australia. Practical implications• There are current methodological concerns in research studies surrounding the influence of body fat on thermoregulation during exercise in the heat • Future investigations need to make unbiased comparisons (i.e. control for confounding factors such as metabolic heat production, body mass, heat acclimatization, body surface area, etc.) between Hi-BF and Lo-BF to examine the independent influence of body fat on thermoregulation during exercise in the heat.

Reference Standard for Digital Infrared Thermography of the Surface Temperature of the Lower Limbs

“…This study has some limitations regarding various intrinsic or extrinsic factors that can influence surface temperature [ 38 , 39 ]. Firstly, the environment of the subjects was not entirely controlled during the DITI exam.…”

Limitations associated with thermoregulation and cardiovascular research assessing laborers performing work in the heat

“…It is well understood that occupational heat stress is a combination of environmental conditions, encapsulating PPE, and heavy physical exertion. This review used environmental conditions to distinguish hot environments as it has been used as a common indicator of heat stress in previously published systematic reviews 77,78 . However, it should be recognized that these inclusion criteria may have excluded studies that have experienced heat stress through physical activity or PPE only.…”

A Special Issue on Heat, Health, and Performance in Journal of Science and Medicine in Sport

“…This is an important consideration for prescription of exercise during training and during competitive events. Morrissey 21 The impact of obesity on thermoregulation during exercise in the heat: A systematic review and meta-analysis Further research is required to adequately determine whether or not obesity independently influences thermoregulation during exercise in the heat. It is recommended that future research continue to employ exercise prescription that accounts for differences in body surface area, body mass and workload.…”