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

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Osborne, John O
Stewart, Ian B
Borg, David N
Beagley, Kenneth W
Buhmann, Robert L
Minett, Geoffrey M
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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 °C, 53 ± 4% relative humidity) or temperate (CON: 22.2 ± 2.6 °C, 65 ± 8% relative humidity) environment. All 20TTs were completed in the heat (35.1 ± 0.5 °C, 51 ± 4% relative humidity). Neuromuscular assessment of knee extensors (5 × 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.

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European Journal of Applied Physiology
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© The Author(s) 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made.
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Osborne, JO; Stewart, IB; Borg, DN; Beagley, KW; Buhmann, RL; Minett, GM, Short-term heat acclimation preserves knee extensor torque but does not improve 20 km self-paced cycling performance in the heat, European Journal of Applied Physiology, 2021, 121 (10), pp. 2761-2772