THE EFFECT OF DRY AND HUMID HEAT ACCLIMATION ON PERFORMANCE IN EACH ENVIRONMENT

Abstract

BACKGROUND Athletes adopt heat acclimation (HA) to partly restore heat-mediated decrements in performance. However, the influence of environmental characteristics during HA on performance in dry and humid conditions is unclear. Therefore, this study aimed to compare dry and humid HA on performance in each environment. METHODS In a counterbalanced crossover study, ten trained male cyclists (age 43 ± 9 y; body mass 80.8 ± 7.3 kg; maximal oxygen uptake; 59 ± 7 mL.kg-1.min-1) completed a 30-min time-trial in hot-dry (TT-DRY; 42°C, 25% RH) and warm-humid (TT-HUM; 33°C, 80% RH) conditions before and after 8 days of controlled heart rate (HR) HA in either dry (DRY-HA) or humid conditions (HUM-HA). A Bayesian multi-level model was used to determine posterior means, 90% credible intervals, and probability of direction (%). RESULTS The improvement in power output during TT-HUM was similar following DRY-HA (13 W [3, 22]; 99%) and HUMID-HA (11 W [3, 19]; 98%). In TT-DRY, the improvement in power output was 12 W ([1, 22]; 97%) higher following DRY-HA (19 W [10, 28]; >99%) compared to HUM-HA (7 W [-2, 17]; 91%). During TT-HUM, mean rectal temperature changed following HUM-HA (0.03°C [-0.11, 0.17]; 63%) and DRY-HA (-0.14°C [-0.29, 0.02]; 92%), with a difference of 0.16°C ([-0.36, 0.03]; 92%). During TT-DRY, the difference was -0.20°C ([-0.40, 0.01]; 94%) between HUM-HA (-0.22°C [-0.38, -0.06]; 98%) and DRY-HA (-0.03°C [-0.19, 0.13]; 63%). Mean HR during TT-DRY (3 beats·min-1 [-2, 8]; 85%) and TT-HUM (-4 beats·min-1 [-10, 2]; 85%) was similar following DRY-HA and HUM-HA. CONCLUSIONS DRY-HA further improved mean power output during TT-DRY compared to HUM-HA. However, HUM-HA tended to lower rectal temperature more than DRY-HA during TT-DRY. HA condition did not influence HR during either TT. Our data indicate that performance is further improved in hot-dry conditions when acclimating to the same environment.