Effect of Precooling On Cardiovascular Drift And Maximal Oxygen Uptake

Abstract

Hot environmental conditions result in substantial cardiovascular drift (CV drift) during exercise, which is proportional to reductions in maximal oxygen uptake (VO2max). Continuous cooling during exercise has been shown to mitigate the magnitude of CV drift and concomitant reduction in VO2max, but it remains unknown if precooling before exercise has similar effects. PURPOSE:To determine if precooling blunts the magnitude of CV drift and accompanying decrement in VO2max during prolonged, constant-rate, submaximal exercise in the heat. METHODS:After a control VO2max test, 5 men cycled on separate days at 60% VO2max for 45 min in 35 °C after being cooled for 20 min (45C) or after no cooling treatment (45NC). After the 45 min, they completed a graded exercise test to measure VO2max. VO2max was also measured after 15 min of cycling at 60% VO2max on a different day (15max), so that CV drift and VO2max could be measured over the same points in time. RESULTS: Precooling successfully lowered mean skin temperature just before the start of exercise (mean ± SD, 32.9 ± 0.4 °C vs. 34.5 ± 1.3 °C for 45C and 45NC, respectively, P 0.05), but rectal (37.0 ± 0.3 °C and 36.7 ± 0.1 °C for 45C and 45NC, respectively, P = 0.51) and mean body temperatures (36.3 ± 0.4 °C and 36.3 ± 0.4 °C for 45C and 45NC, respectively, P = 0.98) were unaffected. During subsequent exercise, the magnitude of CV drift was unaffected by precooling (P > 0.05), and VO2max also was unaffected (45C = 2.49 ± 0.2 L•min-1 vs. 45NC = 2.41 ± 0.2 L•min-1, P = 0.53). CONCLUSIONS: Precooling of the head, neck, quadriceps, calves and torso has no effect on the magnitude of CV drift and decrease in VO2max during subsequent exercise in the heat.