Heat tolerance testing: Association between heat intolerance and anthropometric and fitness measurements

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 [VO_2max]). 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 40ºC and 40% relative humidity. VO_2max 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). VO_2max was the only independent attribute that significantly influenced both the maximum HR and core temperature attained during HTT. Logistic regression analyses indicated that VO_2max 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.