Author(s): HUNTER, B., FUJII, N., MAUNDER, E., MUNIZ-PUMARES, D., Institution: LONDON METROPOLITAN UNIVERSITY, Country: UNITED KINGDOM, Abstract-ID: 1700

INTRODUCTION:
Physiological determinants of endurance performance including peak oxygen consumption (V̇O2peak), the sustainable V̇O2 (e.g., V̇O2 at the first ventilatory threshold [V̇O2 at VT1]), and running economy (RE) deteriorate following prolonged exercise. Durability is the resilience to this decline (1). Heat stress also impairs the determinants of endurance performance (2). However, limited research has examined the combined effects of heat and prolonged running. Therefore, the aim of this study was to determine the effects of heat stress and prolonged running on physiological parameters typically associated with marathon performance. It was hypothesised that the determinants of endurance performance would deteriorate following a prolonged bout of running, and that this deterioration would be exacerbated by heat stress.
METHODS:
Following ethical approval and written informed consent, ten runners (7 M; 3 F; 38 ± 11 yrs; 1.74 ± 0.11 m; 68.2 ± 13.8 kg) completed four trials. Participants first completed incremental tests to determine baseline (PRE) V̇O2peak, V̇O2 at VT1, and speed at VT1 (sVT1), in a temperature-controlled laboratory set at temperate (TEMP; 19°C, 40% RH) or warm (WARM; 30°C, 40% RH) conditions. In subsequent visits, and in a randomised order, the same tests were performed after a 90-min run at a temperature-specific speed (5% Δ between sVT1 and speed at V̇O2peak) in each condition (POST). The order of the first two, and final two visits, were randomised. Core temperature (Tcore), measured using telemetric pills, and RE were measured every 15 min throughout the 90-min run. Repeated-measures ANOVA were used to test for differences in time (PRE vs. POST), condition (WARM vs. TEMP), and interaction effects.
RESULTS:
During prolonged trials, participants ran at 12.0 ± 0.9 km/h (TEMP) and 11.1 ± 1.0 km/h (WARM), covering 18.0 ± 1.3 km and 16.6 ± 1.6 km, respectively. Tcore increased to a greater extent in WARM (Δ1.6 ± 0.6 °C) compared to TEMP (Δ1.0 ± 0.3 °C; p < 0.01). Deterioration in RE from PRE to POST was more pronounced in WARM (+5.4 ± 6.4%) compared to TEMP (+1.7 ± 3.1%; p=0.04). V̇O2peak decreased from PRE to POST (p = 0.04), with no condition effect. Similarly, relative V̇O2 at VT1 and sVT1 decreased from PRE to POST in both conditions (p < 0.01). sVT1 was significantly higher at both time points in the TEMP (PRE: 11.5 ± 0.7 km/h; POST: 10.5 ± 1.1 km/h) compared to WARM (PRE: 10.5 ± 1.1 km/h; POST: 9.6 ± 1.3 km/h) (p < 0.01). No significant interaction effects were evident in V̇O2 at VT1, sVT1, or V̇O2peak.
CONCLUSION:
Prolonged running impairs key physiological determinants of endurance performance. While heat stress did not exacerbate reductions in parameters at VT1 or maximal aerobic capacity following prolonged running, sVT1 was consistently lower in the warm condition and running economy deteriorated to a greater extent in the heat. These findings suggest that heat stress further compromises sustainable running speed and performance following prolonged exercise.