Work

Physiological response to exercise in the heat: Implications for risk mitigation and adaptation

Year: 2024

Type: article

Abstract: Purpose Recentfield studies of physical exertion in challenging environmentalconditions have reported dissociation between elevation in body coretemperature (Tc)and successful task completion. This prompted us to further examinephysiological mechanisms that might underlie variability in theresponse to exertional heat exposure. We hypothesized that, inresponse to exercise in the heat, systematic differences in centraland peripheral physiological variables would be apparent betweenparticipants who successfully completed the task, versus those whobecame hyperthermic or symptomatic.Methods 38healthy participants attempted a 120-min walk (5 km/h, 2%grade) in aclimate-controlled chamber (40⸰C,50%RH). At rest and at regular intervals during the walk, measures ofphysiological heat strain were assessed. Twenty-seven participantswere Completers, seven were stopped because their Tcexceeded 39⸰C(Hyperthermics), and four became Symptomatic (e.g. lightheaded,headache, dizzy)and did not complete the walk.Results Visceraladipose tissue was higher in those who became Hyperthermic, comparedto the Completers (437 ± 183vs 245 ± 268 g; p = 0.034),despite similar height and body mass. Hyperthermics also had higherheart rate (p = 0.009),and lower end-diastolic volume (p = 0.031),and stroke volume (p = 0.031)during the early stages of walking, compared to the Completers. Noneof theSymptomatics reached a Tc >39⸰C(symptoms occurred at 38.1 ± 0.4⸰C),and none of the Hyperthermics reported symptoms.Conclusions Duringexertional heat exposure, adiposity and exaggerated early-stagehemodynamic responses were related to Tcelevation, but hyperthermia was not related to the development ofsymptoms, and baseline parameters relating to body composition andfitness were not related to symptom development.

Source: Temperature

DOI: 10.1080/23328940.2024.2431402