Magni Mohr, Lars Nybo, Justin Grantham, Sebastien Racinais
Sport and Health Sciences, College of Life and Environmental Sciences, St. Lukes Campus, University of Exeter, Exeter, United Kingdom, Department of Exercise and Sport Sciences, Section of Human Physiology University of Copenhagen, Copenhagen, Denmark, Aspetar, Qatar Orthopaedic and Sports Medicine Hospital, Research
and Education Centre, Doha, Qatar.
Purpose: To examine the impact of hot ambient conditions on physical performance and physiological responses during football match-play.
Methods: Two experimental games were completed in temperate (~21˚C; CON) and hot ambient conditions (~43˚C; HOT). Physical performance was assessed by match analysis in 17 male elite players during the games and a repeated sprint test was conducted after the two game trials. Core and muscle temperature were measured and blood samples were obtained, before and after the games.
Results: Muscle and core temperatures were ~1˚C higher (P<0.05) in HOT (40.3+-0.1 and 39.5+-0.1˚C, respectively)
compared to CON (39.2+-0.1 and 38.3+-0.1˚C). Average heart rate, plasma lactate concentration, body weight loss as well as post-game sprint performance were similar between the two conditions. Total game distance declined (P<0.05) by 7% and high intensity running (>14 km/h) by 26% in HOT compared to CON), but peak sprint speed was 4% higher (P<0.05) in HOT than in CON, while there were no differences in the quantity or length of sprints (.24 km/h) between CON and HOT. In HOT, success rates for passes and crosses were 8 and 9% higher (P,0.05), respectively, compared to CON. Delta increase in core temperature and absolute core temperature in HOT were correlated to total game distance in the heat (r = 0.85 and r = 0.53, respectively; P<0.05), whereas, total and high intensity distance deficit between CON and HOT were not correlated to absolute or delta changes in muscle or core temperature.
Conclusion: Total game distance and especially high intensity running were lower during a football game in the heat, but these changes were not directly related to the absolute or relative changes in core or muscle temperature. However, peak sprinting speed and execution of successful passes and crosses were improved in the HOT condition.
Playing football in the heat has been shown to result in high body temperatures, which may have a negative impact on performance and accelerate the development of fatigue during a game. While the total distance covered in a football match may be lower in relation to temperate conditions even in moderate heat, the total game-distance alone has been shown to be a poor football match-performance indicator. With regards to sprint performance, maximal sprint performance may be improved when the muscle temperature is elevated prior to competition,
whereas the ability to perform repeated high intensity exercise has been reported to deteriorate with hyperthermia even though higher muscle temperatures are reached. A possible explanation may be that hyperthermia limits whole-body exercise even before peripheral muscle factors became limiting. Thus, hyperthermia appears to affect various physiological systems and types of physical performance components in a complex manner, making its net-effect on a multi-faceted activity like football difficult to resolve. Only two studies have compared the effect of elevated ambient temperature on match performance in football. Ekblom compared a game at moderate heat (30˚C) to a game at a normal temperature (20˚C), while Ozgunen et al. compared two games in the heat with only two degrees difference. Neither of these studies could elucidate the physiological and performance responses of athletes normally competing in temperate conditions when exposed to severe heat stress (>40˚C) which often occurs during international tournaments and will be expected at the upcoming football World Cup in Qatar in 2022. Mohr et al. have reported that in the last 15 minutes of a football match played in moderately high environmental temperatures (~30˚C), high intensity running decreased markedly and the muscle temperature in some players was in excess of 41˚C at the end of the match. Therefore, it appears that the ability to perform high intensity running towards the end of a match may be more affected in the heat compared to observations from temperate conditions. However, the mechanisms for this response have not been elucidated or directly compared to a matched control situation.