Exercising in exceedingly high temperatures puts significant physiological strain on the body and can markedly impair prolonged physical performance and accelerate time to fatigue (Cheuvront, Kenefick, Montain, & Sawka, 2010). The opening games of the 2014 World Cup in Brazil are imminent with expected temperatures of 30°C and humidity levels reaching 75%. Furthermore, these high values are expected to soar with the prediction of an El Niňo event. England has yet to make it past the quarter-final stages during the previous competitions held outside the temperate conditions of Europe, suggesting that a failure of the players to acclimatise physiologically to the heat could negatively impacted on their performance during the later stages.
Prolonged exercise during hot climatic conditions causes considerable stress on internal physiological systems as an increase in core body temperature and tightening of the thermal gradient of the skin and surrounding environment causes a greater blood flow towards the peripheral system. The resultant decrease in central blood volume is associated with higher cardiovascular strain and impaired aerobic capacity. As a result, the relative exercise intensity is greater and time till exhaustion is rapidly accelerated (Cheung, McLellan, & Tenaglia, 2000). This was demonstrated in elite football players whose total game distance and volume of high intensity sprinting was significantly reduced during a game of football at high temperatures ( 43°C) compared to moderate temperatures ( 21°C), highlighting a direct decline in performance with increased temperature (Mohr, Nybo, Grantham, & Racinais, 2012). Heat stress is exacerbated by substantial increases in sweat production which can lead to dehydration and loss of electrolytes if fluid needs are not met. During a football match, player’s fluid loss can range from 2-5L depending on humidity and can have marked adverse effects on performance as cardiovascular strain is heightened (Reviewed by Shirreffs, 2010).
Conversely however, the players in Mohr’s study had significantly higher peak sprint performance in the higher temperatures with corresponded with considerably enhanced performance quality indicated by more successful passes and ball possession. Slight elevations in central core and local intramuscular temperatures maximise neuronal and biochemical activity leading to greater muscle contractility and higher force production (Cheung et al., 2000). Short bursts of intermittent activity are enhanced which manifests as improved technical performance. However, with few rest intervals during a game lasting 90 minutes or more, repeated bouts of explosive activity at higher temperatures rapidly depletes exercise performance. This is supported by research finding significant declines in distance covered during the second half of matches and declines of 57% in high intensity running time during the final 15 minutes of play compared to the first (Mohr et al., 2012). Therefore, the physiological response of exercise at elevated temperatures acts as a double-edged sword on performance during a football game, emphasising the importance of adopting a strategic approach to maximise competition chances.
Heat adaptation is a physiological response of acclimatisation to increased temperatures allowing improved tolerance to heat stress. Gradual acclimatisation is achieved through repeated exercise sessions at higher temperatures, with significant improvements in exercise capacity and endurance performance seen after 10 days (Lorenzo, Halliwill, Sawka, & Minson, 2010). Adaptations to exercising under heat stress include increased blood plasma volume to adjust for the higher (up to 200%) sweat rates, decreased electrolyte loss and significantly reduced heart rate. What’s more, prolonged heat exposure causes psychological acclimatisation as players become familiar with the heat stress response and perceived exertion is reduced. Responses display high individual variability and coaches and team doctors are advised to monitor players by analysing individual red blood cell count as a measure of acclimatisation. Additionally, such adaptations are beneficial for players during temperate conditions, suggesting that regular ‘heat sessions’ of exercise would increase performance after the competition is over (Lorenzo et al., 2010).
In summary, it is evident that football and exercise performance is altered during heat stress which is likely to have a significant impact on English players from temperature regions during the world cup in Brazil. These alterations however can be utilised beneficially providing an appropriate period of acclimatisation is undertaken prior to the competition and regular monitoring is practised to identify individuals responses to maximise chances of bringing home the cup.