Heat stress may contribute to decreased match performance when football is played in extreme heat. This study evaluated activity patterns and thermal responses of players during soccer matches played in different environmental conditions. Non-acclimatized soccer players (n 5 11, 20 AE 2 years) played two matches in conditions of moderate heat (MH) and high heat (HH) index. Core temperature (T c ) and physical performance were measured using a telemetric sensor and a global positioning system, respectively. The average ambient temperature and relative humidity were MH 34 AE 1 1C and 38 AE 2%; HH 36 AE 0 1C and 61 AE 1%. Peak T c in the MH match was 39.1 AE 0.4 1C and in the HH match it was 39.6 AE 0.3 1C. The total distance covered in the first and second halves was 4386 AE 367 and 4227 AE 292 m for the MH match and 4301 AE 487 and 3761 AE 358 m for the HH match. Players covered more distance (Po0.001) in the first half of the HH match than in the second half. In football matches played at high environmental temperature and humidity, the physical performance of the players may decrease due to high thermal stress.
During a football match played in warm (34.3 AE 0.6 1C), humid (64 AE 2% rh) conditions, 22 male players had their pre-match hydration status, body mass change, sweat loss and drinking behavior assessed. Pre-match urine specific gravity (1.012 AE 0.006) suggested that all but three players commenced the match euhydrated. Players lost 3.1 AE 0.6 L of sweat and 45 AE 9 mmol of sodium during the 90-min match and replaced 55 AE 19% of their sweat losses and hence by the end of the game were 2.2 AE 0.9% lighter. The water volume consumed during the game was highly variable (1653 AE 487 mL; 741-2387 mL) but there was a stronger relationship between the estimated pre-game hydration status and water volume consumed, than between sweat rate and water volume consumed. In a second match, with the same players 2 weeks later in 34.4 AE 0.6 1C, 65 AE 3% rh, 11 players had a sports drink available to them before and during the match in addition to water. Total drink volume consumed during the match was the same, but approximately half the volume was consumed as sports drink. The results indicate that substantial sweat water and electrolyte losses can occur during match play in hot conditions and a substantial water and sodium deficit can occur in many players even when water or sports drink is freely available.
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