Short-term heat acclimation preserves knee extensor torque but does not improve 20 km self-paced cycling performance in the heat

Purpose This study investigated the effect of 5 days of heat acclimation training on neuromuscular function, intestinal damage, and 20 km cycling (20TT) performance in the heat. Methods Eight recreationally trained males completed two 5-day training blocks (cycling 60 min day(-1) at 50% peak power output) in a counter-balanced, cross-over design, with a 20TT completed before and after each block. Training was conducted in hot (HA: 34.9 +/- 0.7 degrees C, 53 +/- 4% relative humidity) or temperate (CON: 22.2 +/- 2.6 degrees C, 65 +/- 8% relative humidity) environment. All 20TTs were completed in the heat (35.1 +/- 0.5 degrees C, 51 +/- 4% relative humidity). Neuromuscular assessment of knee extensors (5 x 5 s maximum voluntary contraction; MVC) was completed before and after each 20TT and on the first and last days of each training block. Results MVC torque was statistically higher after 5 days of HA training compared to CON (mean difference = 14 N m [95% confidence interval; 6, 23]; p < 0.001; d = 0.77). However, 20TT performance after 5 days of HA training was not statistically different to CON, with a between-conditions mean difference in the completion time of 68 s [95% confidence interval; - 9, 145] (p = 0.076; d = 0.35). Conclusion Short-term heat acclimation training may increase knee extensor strength without changes in central fatigue or intestinal damage. Nevertheless, it is insufficient to improve 20 km self-paced cycling performance in the heat compared to workload-matched training in a temperate environment. These data suggest that recreationally trained athletes gain no worthwhile performance advantage from short-term heat-training before competing in the heat.

Automated summary

Short-term heat acclimation training may increase knee extensor strength without changes in central fatigue or intestinal damage. However, this type of training is insufficient to improve 20 km self-paced cycling performance in the heat compared to workload-matched training in a temperate environment.