FEATURE: HEAT STRESS HEAT ACCLIMATISATIO FOR THE2018 FIF WORLD CU HEAT STRESS DURING temperature can reach and exceed SOCCER 39°C, even during matches played in cool conditions. JULIEN D PÉRIARD The 2018 FIFA World Cup will be held in Russia from June 14 to July 15. The When soccer is played in the heat, peak expected temperature across the core temperature can reach values more ASSOCIATE PROFESSOR, diff erent host cities is likely to be between than 1ºC higher relative to when played in UNIVERSITY OF CANBERRA 20 and 25ºC, with hot days exceeding cool conditions, often exceeding 40ºC 30ºC and relative humidity hovering (Mohr et al., 2012). Consequently, fatigue RESEARCH INSTITUTE FOR between 60 and 80%. Although these profi les are more pronounced at the end SPORT AND environmental conditions are not of matches in the heat than those in more considered an extreme risk for the temperate environments, with less EXERCISE (UCRISE) occurrence of exertional heat illness, they distance covered in the second half of may pose a high risk for athletes who are matches (Özgünen et al., 2010). The unaccustomed to hot/humid conditions, amount of high-intensity running is also or those with a compromised immune about 50% lower during the fi nal 15 min system (e.g. having recently experienced of a match in the heat compared with the a cold or fl u). The combination of fi rst 15 min, whilst repeated sprinting and environmental conditions and metabolic jumping ability are compromised post- heat production during play may also relative to pre-match (Mohr et al., 2010). infl uence performance. Similar alterations in match characteristics were noted during the Indeed, at the elite level players typically 2014 FIFA World Cup in Brazil, where cover 10 to 13 km and perform 150 to the number of sprints performed during 250 brief intense actions (e.g. tackles, a match was approximately 10% lower in accelerations) during a soccer match conditions of high, relative to moderate (Mohr et al., 2003). This activity pattern or low environmental heat stress (Nassis is infl uenced by position and playing style, et al., 2015). The distance covered at a with mid-fi elders generally covering high intensity was also lower in the heat. greater distances than forwards and These adjustments in performance are backs. Whilst most of this distance is suggested to stem in part from the level covered at a walking or low-intensity of hyperthermia attained, and/or the loss running speed, mean heart rate during of body fl uids via sweating, leading to matches seldom falls below 65% of dehydration (Mohr et al., 2010). maximum due to the elevated frequency of high intensity eff orts. As a result, mean HEAT ACCLIMATISATION AND oxygen uptake during a match remains at FOOTBALL PERFORMANCE /home/webapps/asp_au/data/asp/publications/au-sports-medecine-australia/publications/sport-health-volume-36-june-2018/sport-health-volume-36-issue-170% of maximal aerobic capacity. Given this level of exertion and the demand Although the infl uence of hot on aerobic and anaerobic metabolism environmental conditions cannot be over the duration of a match, core completely circumvented, training in the 22 VOLUME 36 • JUNE ISSUE 2018