Heat stress and the velocity–duration relationship in amateur runners

Abstract

Tolerance to high‐intensity constant power exercise can be characterized by the hyperbolic power‐duration (or velocity–duration) relationship. The hyperbola is defined by the asymptote (critical power or velocity) and the curvature constant (W′ or D′). The effects of thermoregulatory stress on middle‐distance running performance are equivocal—possibly due to the complexities of the hyperbolic velocity–duration relationship for these relatively short duration events. We aimed to measure the effects of heat stress on the velocity–duration relationship in amateur runners. Fifteen participants (23 ± 6 years) completed a series of constant‐velocity running bouts to intolerance in three heat indices (MILD: 20°C, VERY HOT: 38°C, EXTREME: 55°C). Critical velocity (CV) in MILD (3.52 ± 0.86 m/s) was higher than VERY HOT (3.39 ± 0.82 m/s) and EXTREME (3.29 ± 1.05 m/s; F[2.28] = 3.80, p < 0.035) with no effect of thermal stress on D′ (F[2.28] = 2.48, p = 0.11). In amateur competitive/recreational runners, heat stress of ≥38°C heat index negatively affected CV. Thus, even during relatively short events, such as middle‐distance running where fluid loss is not a primary concern, heat stress may negatively impact performance.