Upper body sweat mapping provides evidence of relative sweat redistribution towards the periphery following hot-dry heat acclimation

Purpose: Produce a detailed upper-body sweat map and evaluate changes in gross and regional sweating rates (RSR) and distribution following heat acclimation (HA). Methods: Six male participants (25±4 yrs) completed six consecutive days of HA (45°C,20% rh) requiring 90 minutes of intermittent exercise to maintain a rectal temperature (Tre) increase of 1.4°C. RSR were measured at 55% (Intensity-1; I1) and 75% V̇O2max (Intensity-2; I2) on the upper-body pre- and post-HA using a modified absorbent technique. Results: By design, work rate increased from day one to six (n.s.) of HA, and heart rate (HR), Tre, and skin temperature (Tsk) were similar between days. Gross sweat loss (GSL) increased (656±77 to 708±80g.m-2 .h-1 ; P<0.001) from day one to six. During pre- and post-acclimation experiments, relative workloads were similar for both intensities (Pre-I1 54±3, Post-I1 57±5 %VO2max; Pre-I2 73±4, Post-I2 76±7 %VO2max). GSL was significantly higher post-HA (Pre 449±90 g.m-2 .h-1 , Post 546 g.m-2 .h-1 ; P<0.01). Highest RSR were observed on the central back both pre and post acclimation at I1 (pre 854±269 post 1178±402g.m 2 .h-1 ) and I2 (pre 1221±351 post 1772±396 g.m-2 .h-1 ). Absolute RSR increased significantly in 12 (I1) to 14 (I2) of the 17 regions. Ratio data indicated significant relative RSR redistribution following HA, with the relative back contribution to whole-body sweat loss decreasing, chest staying the same and the arms increasing. Conclusions: Hot-dry HA significantly increased GSL in aerobically trained males at I2 only. Absolute RSR significantly increased in I1 and I2, with a preferential relative redistribution towards the periphery of the upper body.