Core temperature responses of male football players during matches in the heat — Associations with physiological and running demands

Objectives This study describes core temperature (T core ) responses during football matches in warm to hot conditions. It aims to identify which physiological, running, and perceptual factors are associated with reaching high T core values whilst controlling for environmental conditions and cooling. Design Forty highly trained male youth football players participated in at least two out of four matches held at temperatures between 26 and 42 °C Temperature. In three matches, heat mitigation strategies (passive rest and 17 °C drinks, or cold towels and 5 °C drinks) were applied pre-match, at half-time, and in additional breaks per half. Method Match running, heart rates, hydration markers, and perceptual responses were measured and checked for associations with peak T core values via linear mixed models accounting for environmental conditions and heat mitigation strategies. Results Peak T core was 39.2 ± 0.5 °C (range: 37.9–40.1 °C). Higher total distance (β = 0.39[0.13,0.64], p = 0.004) and distance at low-to-moderate speeds (β = 0.44[0.18,0.69], p = 0.001) were associated with higher peak T core , while walking distance was inversely associated (β = −0.42[−0.69,-0.15], p = 0.003). High-speed and sprinting distance were not associated with peak T core . Higher heart rate (β = 0.37[0.10,0.64], p = 0.008), sweat loss (β = 0.38[0.14,0.62], p = 0.002) and body mass loss (β = 0.20[0.00,0.40], p = 0.047) were also associated with higher peak T core . Rating-of-fatigue ( p = 0.74 ), perceived exertion ( p = 0.78 ), and thermal sensation ( p = 0.98 ) were not associated with peak T core . Conclusions High T core peaks were observed in all conditions and were associated with higher heart rate, sweat loss, and match running. Covering more distance at low-to-moderate speed was associated with a higher heat strain, whereas walking more (instead of running) was associated with lower T core peaks.