Durability of Physiological Determinants of Distance‐Running Performance in Warm and Temperate Environments

Runners increasingly train and compete in warm conditions, yet it is unclear whether heat stress accelerates the deterioration of the physiological determinants of distance-running performance during prolonged running. Ten trained runners (7 M; 3 F; 38 ± 11 years; peak oxygen uptake (V̇O₂peak): 56.0 ± 5.7 mL·kg−1·min−1) visited the laboratory on four occasions. In randomized order, participants completed incremental tests to determine the first ventilatory threshold (VT₁), V̇O₂peak, and end-test speed in temperate (TEMP; 19°C) and warm (WARM; 30°C; both 40% relative humidity) conditions in a “fresh” state (PRE). Tests were repeated (POST) after 90 min of running in the same condition at 5% Δ between the speed at VT₁ (sVT₁) and end-test speed. Running economy was measured at 15-min intervals throughout. In the rested state, sVT₁ was ~7% (~0.8 km·h−1) lower in WARM than TEMP, and declined after prolonged running in both conditions (TEMP: −8.6%; WARM: −11.1%), with no condition × time interaction. V̇O₂peak was reduced after prolonged running (TEMP: −4.8%; WARM: −4.0%), with no condition × time interaction. In contrast, running economy deteriorated to a greater extent in WARM (+5.4% vs. +1.7% from 15 to 90 min), and end-test speed declined more in WARM than TEMP (−12.1% vs. −6.8%). We found no evidence that heat altered the durability of sVT₁ and V̇O₂peak when intensity was prescribed relative to condition-specific capacity. However, sVT₁ was already lower in WARM before prolonged running, so that after prolonged running it was, on average, 17.1% below the rested value in TEMP.