Dietary Carbohydrates Influence the Performance Outcomes of Short-Term Heat Acclimation.

Abstract

PURPOSE Studies on heat acclimation (HA) involving high-intensity exercise report impairments in time trial (TT) performance in the heat immediately after HA. This study aimed to determine whether a high-carbohydrate (HC) diet can enhance 3.22 km run TT performance in the heat following exercise-intensive short-term HA. METHODS Fourteen healthy military-age males were assigned to either a HC diet (70 %kcal carbohydrate (CHO), n = 7) or lower CHO comparison (COMP, 35 %kcal CHO, n = 7) to be consumed during and for one week after a 6-day HA protocol. RESULTS Baseline descriptive statistics, heat tolerance, and run performance were similar between groups (p > 0.05). Both groups acclimated, showing reduced heart rate, rectal and skin temperature, and increased sweat rate (each p ≤ 0.03) during heat stress testing one day and five days after HA. The HC group demonstrated a faster TT (959 ± 103 sec vs. 1067 ± 172, p = 0.02, g = 0.71) than COMP one day post-HA. HC showed improved TT performance from baseline at one day (p = 0.01, g = 0.59) and five days post-HA (p = 0.04, g = 0.59). The HC group showed greater TT improvement at one day (-7.0 ± 4.9 % vs. -0.7 ± 4.7 %, p = 0.03, g = 1.23) and five days post-HA (-8.4 ± 4.9 % vs. -2.8 ± 3.9 %, p = 0.01, g = 1.18), with no group differences in HA outcomes or relative strain during TT. CONCLUSIONS Insufficient CHO intake during heavy daily exertion in unacclimated heat stress, such as in short-term HA, may affect post-HA performance outcomes unless addressed with additional CHO consumption.