Comparison of lower- vs. upper-body cooling during arm exercise in hot conditions.

Introduction: Studies examining cooling strategies and exercise have generally employed lower-body exercise despite the fact that arm exercise is an important mode for many industrial tasks and disabled populations. The aim of this study was to determine the effects of two cooling strategies during arm exercise in the heat.

Methods: There were eight male subjects (mean +/- SD age 24.5 +/- 4.0 yr, weight 81.0 +/- 7.8 kg, upper-body VO2peak 3.13 +/- 0.50 L x min(-1)) who volunteered for this study. Subjects undertook arm crank exercise for 30 min (50% VO2peak) in a hot environment (40.2 +/- 0.4 degrees C, 38.7 +/- 7.4% RH) on three occasions (no cooling control, CON; lower-body cooling, LC; upper-body cooling, UC).

Results: No differences were observed between trials for oxygen consumption, respiratory exchange rate (RER), or blood lactate. Heart rate (HR) was greatest during CON (151 +/- 11 bpm) when compared with UC and LC (148 +/- 16 and 138 +/- 13 bpm; p < 0.05). Mean skin temperature was warmer during CON (36.3 +/- 0.5 degrees C) when compared with UC (31.2 +/- 1.4 degrees C, p < 0.05), which was warmer than during LC (28.5 +/- 1.3 degrees C, p < 0.05). No differences were observed for rectal or aural temperatures between trials. At the end of exercise, heat storage was hyperthermic (3.04 +/- 0.68 J x g(-1)), thermoneutral (0.18 +/- 1.21 J x g(-1)), and hypothermic (-2.37 +/- 0.81 J x g(-1)) during CON, UC, and LC, respectively (p < 0.05). Perceived exertion was lowest during LC and greatest during CON (p < 0.05).

Conclusions: The results of this study suggest that cooling the lower body during arm exercise in hot conditions is more effective in reducing physiological and thermal strain than cooling the upper body.