When Should a Heat-Tolerance Test Be Scheduled After Clinical Recovery From an Exertional Heat Illness?

Abstract

Objective Researchers have produced a hypothesis of transient heat intolerance (HI) after exertional heat stroke (EHS). Based on this hypothesis, heat-tolerance testing (HTT) has been postponed until weeks 6 to 8 after EHS and other types of exertional heat illness (EHI). We compared the HTT results of participants after either EHS or other EHI who were tested earlier (≤6-week group) versus those who were tested later (>6-week group) to verify the hypothesis. Design Cohort study. Setting Data obtained from records of military athletes who experienced EHS or EHI. Patients or Other Participants All participants who underwent HTT after EHI or EHS experienced between 2014 and 2018 and for whom complete data regarding the severity of the event (rectal temperature, neurologic symptoms, and laboratory results) and HTT results were available were included. Participants with suspected EHS and those with other EHIs were evaluated separately. Main Outcome Measure(s) The percentages of participants with HI and mean probability of heat tolerance were compared between those tested within 6 weeks of the event and those tested later. Results A total of 186 participants were included in this study (EHS: 12 in the <6-week group, 9 in the >6-week group; EHI: 94 in the <6-week group, 71 in the >6-week group). In the EHS group, the percentages with HI (33% versus 44%, P = .67) and mean probability of heat tolerance (0.82 versus 0.82, P = .98) did not differ. In the EHI group, participants who were tested after 6 weeks had a greater chance of being diagnosed with HI (38% versus 21.3%, P < .02) Conclusions The HTT results were similar between participants with EHS who were tested early (<6 weeks) and those tested late (>6 weeks). Further investigation of heat-tolerance changes in larger cohorts of patients after EHS is required to verify the theory of transient HI.

Individual Anthropometric, Aerobic Capacity and Demographic Characteristics as Predictors of Heat Intolerance in Military Populations

“…However, individuals vary in their ability to tolerate heat stress and the inability to maintain thermal balance while exercising in a hot environment is known as heat intolerance [ 5 , 6 , 7 ]. Previous studies have reported that heat intolerance may be a by-product of inherent impaired thermoregulatory mechanisms or may occur as a direct result of exertional heat stroke (EHS) [ 8 , 9 ].…”

Haematological, Biochemical and Hormonal Biomarkers of Heat Intolerance in Military Personnel

“…On the other hand, severe heat exposure and exhausting physical activity have a suppressant effect causing a temporary increase in susceptibility to infections and EHS [32]. Given that EHS may precede or accompany heat intolerance, it is essential to identify the biomarkers predictive of heat intolerance [14,33]. In the current study, there are significant differences in the baseline and post-test values for ALT, creatine kinase, creatinine and cortisol among the heat-intolerant group compared to the heat-tolerant group.…”

Current Clinical Concepts: Heat Tolerance Testing

“…An important and frequently overlooked factor to consider with HTT is the fitness level of the individual. Most studies have only assessed HTT in well-trained athletes (including tactical), 4,8,21 even though individuals with lower physical fitness are at the greatest risk for EHS.…”

“…30 Therefore, increased time between HTT trials or time spent in recovery from an EHS may result in loss of any potential heat acclimation or training adaptations already achieved. Additionally, while most research on HTT involves males, 4,8,21 emerging evidence suggests sex-dependent factors influence thermoregulation in general and heat acclimation adaptations specifically. As such, future HTT interpretations should consider potential sex and menstrual cycle phase differences.…”

“…Furthermore, the lack of clear indication marking recovery from, and potential reoccurrence of, an EHS presents a gap in the current clinical decision making process, creating a potential role for heat tolerance testing (HTT). Emerging HTT protocols and variables considered in the interpretation of the test require further consensus 2,4 to validate the critical role HTT can play in guiding RTA, tracking fitness, and monitoring heat acclimation progress. 3 Traditionally, HTT has been performed following an EHS to determine an individual's ability to respond to heat in a thermally stressful environment, or heat tolerance, and is considered a functional measure for return to activity.…”