Heat Tolerance Testing: Association Between Heat Intolerance and Anthropometric and Fitness Measurements

Abstract

This study investigated associations between heat intolerance, as determined by performance on a heat tolerance test (HTT), and anthropometric measurements (body surface-to-mass ratio, percent body fat, body mass index, and waist circumference) and cardiorespiratory fitness (maximal oxygen uptake [VO2max]). Relationships between predictive variables and specific physiological measurements recorded during the HTT were examined. A total of 34 male and 12 female participants, recruited from the military community, underwent anthropometric measurements, a maximal aerobic exercise test, and a standardized HTT, which consisted of walking on a treadmill at 5 km/h at 2% grade for 120 minutes at 40°C and 40% relative humidity. VO2max negatively correlated with maximum core temperature (r = -0.30, p < 0.05) and heart rate (HR) (r = -0.48, p < 0.01) although percent body fat showed a positive correlation with maximum HR (r = 0.36, p < 0.05). VO2max was the only independent attribute that significantly influenced both the maximum HR and core temperature attained during HTT. Logistic regression analyses indicated that VO2max was the only independent parameter (OR = 0.89, p = 0.026) that significantly contributed to overall HTT performance. Low cardiorespiratory fitness was associated with heat intolerance, as defined by HTT performance, and can be addressed as a preventative measure for exertional heat illness. This study provides further evidence that the HTT can be an effective tool for assessment of thermoregulatory patterns.

Thermal stress, human performance, and physical employment standards

“…The HTT has been in use by the IDF since 1983 and the investigators have suggested that it is useful and effective for identifying heat intolerance (Kazman et al 2013;Lisman et al 2014;Moran et al 2007). Soldiers who passed the HTT and fully resumed duty reportedly did not suffer a subsequent bout of heat injury (Epstein and Heled 2013;McDermott et al 2007).…”

“…Several researchers also recommend using the HTT to assist in return-to-duty/play decisions for post heat-illness individuals (Kazman et al 2013;McDermott et al 2007;O'Connor et al 2007). Yet, the United States military does not adopt the HTT for this purpose (Kazman et al 2013;Lisman et al 2014). The validity of the HTT has also been questioned (Johnson et al 2013;O'Connor et al 2010).…”

“…For example, it is unclear whether the HTT can predict the occurrence of future heat-related illnesses (O'Connor et al 2010). Furthermore, the standards used in the HTT may be biased against females (Druyan et al 2012;Lisman et al 2014). Compared with males, females were more likely to exceed the upper limits of heat tolerance set in the HTT and be deemed as heat intolerant, perhaps because of sex differences in physiologic make-up and thermoregulatory patterns (Druyan et al 2012;Lisman et al 2014).…”

“…Furthermore, the standards used in the HTT may be biased against females (Druyan et al 2012;Lisman et al 2014). Compared with males, females were more likely to exceed the upper limits of heat tolerance set in the HTT and be deemed as heat intolerant, perhaps because of sex differences in physiologic make-up and thermoregulatory patterns (Druyan et al 2012;Lisman et al 2014). The issue of whether the standards should be modified for females is pertinent as more females are entering the military (Druyan et al 2012).…”

Protective clothing ensembles and physical employment standards

“…Further, the test really does not assess "tolerance" as the cardiovascular and core temperature responses represent a compensable or plateau response to the exercise and heat stress. Those that are identified as "intolerant" have a lower level of aerobic fitness and higher body fatness (Lisman et al 2014), and many would probably not be successful during the current PES testing. Instead, the heat tolerance test should create an uncompensable condition, which is more typically associated with wearing PCE, where core temperature and heart rate would continue to increase with continued exposure to the exercise and hot conditions.…”