Effect Of Adding Heat Stress By Wearing Layers During Endurance Training On Improvement Of Exercise Performance

Heat acclimation (HA) prevents performance deterioration in a hot environment. Conventionally, HA can be acquired by repetitive exercise sessions in a hot environment (Racinais et al., 2019). To acquire HA, daily prolonged exercise (60-90 min) in a hot environment for about 2 weeks is currently recommended (Lundby et al., 2021). In this case, an environmental chamber and a period of 10-14 days are required (Periard et al., 2015). In the present study, we focused on adding heat stress by layered clothing to create a hot environment during exercise. PURPOSE: To clarify the effects of heat stress added by layered clothing during 5 days of endurance training on improvement of exercise performance. METHODS: 16 males were separated into two groups, either WEAR group or CON group. They conducted 5 consecutive days of endurance (cycling) training, consisting of 95 min/day at 10 °C with layered clothing (WEAR group) or short-sleeve shirts and short (CON group). During the training sessions, core temperature, skin temperature, heart rate, sweat rate, score of thermal sensation and rate of perceived exertion were evaluated. Before and after training period, V•O2max test and heat stress test (HST) were conducted. HST consisted of 30 min of endurance (cycling) exercise in a hot environment (35 °C, 50%RH) . The measurements during HST were identical shown in training session. RESULTS: V•O2max was significantly increased in the WEAR group after the training period (52.41 vs. 55.24 mL/min/kg, P = 0.002), with no significant main effect of group and interaction of period×group (P > 0.05). The CON group did not show significant change (50.76 vs. 51.95 mL/min/kg, P > 0.05). Resting core temperature did not change in both groups after the training period (WEAR; 37.12 vs. 37.14 °C, CON; 37.14 vs. 36.95 °C, P > 0.05). CONCLUSION: Adding heat stress by wearing layers during endurance training improved V•O2max under thermoneutral environment. However, thermoregulatory ability did not improve.