The influence of whole-body vs. torso pre-cooling on physiological strain and performance of high-intensity exercise in the heat

Little research has been reported examining the effects of pre-cooling on high-intensity exercise performance, particularly when combined with strategies to keep the working muscle warm. This study used nine active males to determine the effects of pre-cooling the torso and thighs (LC), pre-cooling the torso (ice-vest in 3°C air) while keeping the thighs warm (LW), or no cooling (CON: 31°C air), on physiological strain and high-intensity (45-s) exercise performance (33°C, 60% rh). Furthermore, we sought to determine whether performance after pre-cooling was influenced by a short exercise warm-up. The 45-s test was performed at different (P < 0.05) mean core temperature [(rectal + oesophageal)/2] [CON: 37.3 ± 0.3 (S.D.), LW: 37.1 ± 0.3, LC: 36.8 ± 0.4°C] and mean skin temperature (CON: 34.6 ± 0.6, LW: 29.0 ± 1.0, LC: 27.2 ± 1.2°C) between all conditions. Forearm blood flow prior to exercise was also lower in LC (3.1 ± 2.0 ml 100 ml tissue^-1 min^-1) than CON (8.2 ± 2.5, P = 0.01) but not LW (4.3 ± 2.6, P = 0.46). After an exercise warm-up, muscle temperature (T_m) was not significantly different between conditions (CON: 37.3 ± 1.5, LW: 37.3 ± 1.2, LC: 36.6 ± 0.7°C, P = 0.16) but when warm-up was excluded, T_m was lower in LC (34.5 ± 1.9°C, P = 0.02) than in CON (37.3 ± 1.0) and LW (37.1 ± 0.9). Even when a warm-up was performed, torso + thigh pre-cooling decreased both peak (-3.4 ± 3.8%, P = 0.04) and mean power output (-4.1 ± 3.8%, P = 0.01) relative to the control, but this effect was markedly larger when warm-up was excluded (peak power -7.7 ± 2.5%, P = 0.01; mean power -7.6 ± 1.2%, P = 0.01). Torso-only pre-cooling did not reduce peak or mean power, either with or without warm-up. These data indicate that pre-cooling does not improve 45-s high-intensity exercise performance, and can impair performance if the working muscles are cooled. A short exercise warm-up largely removes any detrimental effects of a cold muscle on performance by increasing T_m.