Biological variation of local sweating measures during exercise‐heat stress in heat acclimated humans

Abstract

Local sweat rate (SR) and sweat onset time (SO) can be altered by numerous factors, but the importance of the effect magnitude is uncertain due to poorly characterized components of biological variation in thermoregulatory sweating. Purpose to determine the analytical variation (CVa), individual variation (CVi), group variation (CVg) and bilateral differences of local SR and SO. After completing a heat acclimation program, 2 women and 8 men (26 ± 9 yrs; 79 ± 12 kg) walked (645 watts) on 3 separate occasions, for 30 min in 40°C, 20% rh, while local SR and SO were measured via dew point hygrometry. Hydration and diurnal effects were carefully controlled. SR (2.14 ± 0.72 vs. 2.02 ± 0.79 vs. 2.31 ± 0.72 mg/cm2/min, p=0.19) and SO (10.04 ± 2.97 vs. 9.87 ± 3.44 vs. 10.47 ± 2.54 min, p=0.82) were not different among days. SR (2.14 ± 0.72 vs. 2.16 ± 0.71 mg/cm2/min, p=0.56) and SO (10. 47 ± 2.54 vs.10.83 ± 2.48 min, p=0.09) were not different between arms. CVa of ≤5% is considered optimum for laboratory analytics. CVa, CVi and CVg were 2.4%, 18.8% and 56.4% for SR and 0%, 9.6% and 41% for SO, respectively. Data suggests that ventilated capsules have low imprecision. In heat acclimated humans, both SR and SO measures appear interchangeable between arms. Lower variation within SO suggests greater sensitivity vs. SR when studying factors that potentially affect sweating. Opinions should not to be construed as official views of the Army or DoD.