Temperate performance and metabolic adaptations following endurance training performed under environmental heat stress

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
We observed that 3 weeks of endurance training performed in 33°C improved endurance performance in temperate conditions to a significantly greater extent than matched training performed in 18°C. We also observed a significant increase in vastus lateralis citrate synthase activity in response to training performed in 33°C, but not matched training performed in 18°C.