Abstract
Endurance athletes are frequently exposed to environmental heat stress during training. We investigated whether exposure to 33°C during training would improve endurance performance in temperate conditions and stimulate mitochondrial adaptations. Seventeen endurance‐trained males were randomly assigned to perform a 3‐week training intervention in 18°C (TEMP) or 33°C (HEAT). An incremental test and 30‐min time‐trial preceded by 2‐h low‐intensity cycling were performed in 18°C pre‐ and post‐intervention, along with a resting vastus lateralis microbiopsy. Training was matched for relative cardiovascular demand using heart rates measured at the first and second ventilatory thresholds, along with a weekly “best‐effort” interval session. Perceived training load was similar between‐groups, despite lower power outputs during training in HEAT versus TEMP (p < .05). Time‐trial performance improved to a greater extent in HEAT than TEMP (30 ± 13 vs. 16 ± 5 W, N = 7 vs. N = 6, p = .04), and citrate synthase activity increased in HEAT (fold‐change, 1.25 ± 0.25, p = .03, N = 9) but not TEMP (1.10 ± 0.22, p = .22, N = 7). Training‐induced changes in time‐trial performance and citrate synthase activity were related (r = .51, p = .04). A group × time interaction for peak fat oxidation was observed (Δ 0.05 ± 0.14 vs. −0.09 ± 0.12 g·min−1 in TEMP and HEAT, N = 9 vs. N = 8, p = .05). Our data suggest exposure to moderate environmental heat stress during endurance training may be useful for inducing adaptations relevant to performance in temperate conditions.
Highlights
A goal of endurance training is to induce physiological adaptations that improve determinants of endurance performance such as maximum oxygen uptake (V O2max ), physiological thresholds, and exercise economy (Holloszy, 2008)
Our data suggest exposure to moderate environmental heat stress during endurance training may be useful for inducing adaptations relevant to performance in temperate conditions
What is the central question of this study? We investigated the hypothesis that a 3-w eek endurance training intervention performed under moderate environmental heat stress would improve endurance performance in temperate conditions and metabolic adaptations to training compared to matched training performed in temperate conditions
Summary
A goal of endurance training is to induce physiological adaptations that improve determinants of endurance performance such as maximum oxygen uptake (V O2max ), physiological thresholds, and exercise economy (Holloszy, 2008). Endurance athletes competing in stochastic, drafting events such as road cycling (Lucía et al, 1999) would likely benefit from adequate metabolic flexibility to effectively utilize fat as an energy substrate at given submaximal workloads in order to preserve finite endogenous carbohydrate stores, alongside well-developed, rapid carbohydrate metabolism to facilitate short periods of intense effort (Hawley et al, 2018) These adaptations are at least partly mediated through effects on skeletal muscle mitochondrial content and function, which have been shown to adapt in response to endurance training (Granata et al, 2016a, 2016b; Hoppeler et al, 1985; Montero et al, 2015; Scalzo et al, 2014; Spina et al, 1996). There has been no investigation of mitochondrial adaptations to a heat stress training intervention in endurance athletes
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