Steady‐state local sweat rate is determined by the evaporation required for heat balance relative to body surface area (1104.9)

Abstract

Recent evidence suggests whole‐body sweat rate (WBSR, g·min–1) is determined by the absolute evaporation required for heat balance (Ereq, W). However, since differences in body surface area (BSA) should theoretically modify local sweat rate (LSR, mg·cm–2·min–1) for a given absolute Ereq, we hypothesized that LSR is determined by Ereq relative to BSA (W·m–2) rather than absolute Ereq (W). Sixteen males of large (L: 2.12±0.09 m2, n=8) and small (S: 1.80±0.09 m2, n=8) BSA cycled in 25°C at workloads eliciting Ereq of 340 and 400 W, and 165 and 190 W·m–2. Heat production was estimated via indirect calorimetry. WBSR was estimated from changes in body mass between 45 and 60 min, and LSR was taken as the mean of back and forearm ventilated capsule measurements from 45‐60 min. WBSR was similar between groups at 340 and 400 W (p蠅0.54), but LSR was greater at 400 W (p=0.03), and 340 W (p=0.07), in S. At 165 and 190 W·m–2, no differences in LSR were evident (p蠅0.86), while WBSR was greater in L at 165 W·m–2 (p=0.01) but not at 190 W·m–2 (p=0.13). Differences in BSA modify LSR for a given absolute Ereq, while the prescription of Ereq in W·m–2 results in similar LSR irrespective of BSA.Grant Funding Source: Supported by a NSERC Discovery Grant (O. Jay)