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Blog: Exercising in the Heat - Strategies to Stay Cool

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Sport Scientist at St Mary’s University, Twickenham Paul Hough has written his top tips for keeping cool when exercising in the heat in his latest blog. The European Football Championships and Wimbledon, two of the largest sporting events of the year, will be taking place over the course of June and July. Both football and tennis involve high-intensity intermittent exercise which generates a considerable amount of body heat, which causes an increase in body temperature and sweat rate. The added heat strain from competing in hot conditions increases athletes’ chances of developing an excessive body temperature (hyperthermia), which can have a negative impact on health and performance. Humans have an inherent thermostat which regulates body temperature and prevents hyperthermia. This mechanism causes exercise performance to significantly decrease when a critical core temperature (approximately 40°C) is reached (Gonzalez-Alonso et al., 1999). This ‘safety mechanism’ is thought to prevent the body from reaching temperatures that could potentially lead to fatal heat illness. Therefore, in order to prevent athletes developing hyperthermia and subsequent decreases in performance when competing in the heat, a number of cooling strategies have been studied. These strategies have been studied before (pre-cooling) and during exercise. Pre-cooling Pre-cooling (PC) involves reducing core temperature prior to exercise; this can be achieved through a variety of cooling methods before competing: cool water-immersion, cold water showering, cold air exposure, and wearing cooling garments (e.g. ice vests). Implementing PC can lead to an improvement in exercise performance by reducing the rise in core temperature at the onset of exercise in the heat and increasing the body’s ability to store heat. For example, wearing an ice jacket during an active warm-up in hot conditions (32°C) has been shown to improve 5 km run performance (Arngrimsson et al., 2004). Improvements in performance have also been observed in cyclists using a cool water immersion PC strategy prior to a 30 minute cycling test in hot (31°C) conditions despite the fact that the PC did not significantly decrease core temperature (Kay et al., 1999). Therefore, PC may improve performance by reducing the athlete’s perception of effort due to them feeling cooler. Additionally, there is a possibility of a placebo effect from PC, i.e. the athlete has the expectation that pre-cooling will improve their performance. Cooling during exercise Cooling strategies before exercising in hot conditions may offer potential performance benefits. However, these strategies are impractical to implement during competition. For example, wearing cooling vests during exercise can cool the torso, but the extra weight of the vest increases energy expenditure and can be uncomfortable (Arngrimsson et al., 2004). A more practical solution is to cool the head, neck or hands as these areas can be cooled effectively with minimal disruption to sporting actions or attire. The head and neck are also close to the thermoregulatory centre located at the base of the brain, meaning the temperature of the blood reaching the brain may be cooled. This may provide a false signal to the brain that masks the extent of the thermal strain being experienced, allowing the athlete to tolerate a higher core temperature and thermal strain. This has potential performance-enhancing implications, as athletes can maintain higher exercise intensities following neck cooling (Tyler & Sunderland, 2008). However, caution must be exercised when using neck/head cooling during exercise in a hot environment, as if the thermal strain experienced is masked heavily due to the cooling, the dampening of the body’s natural ‘thermostat’ might allow the athlete to develop an excessively high body temperature and heat illness. Practical application Pre-cooling (PC) is an effective strategy to reduce the debilitating effects of heat-stress-induced fatigue and can enhance exercise performance. PC can be performed during or following a warm-up when cold garments are used. Drinking cold fluids can also potentially enhance endurance performance when ingested before exercise (Byrne et al., 2011). Cooling strategies can also be used during designated rest periods during competition. For example cooling the neck region using a cold towel or cold compress can enable athletes to tolerate higher core temperatures, perceived thermal comfort and ratings of perceived exertion when exercising in a hot environment, which may facilitate exercise performance. However, using neck cooling to dampen the perceived level of thermal strain should be avoided for long periods during competition (e.g. during a race). The use of neck cooling for short periods (5 minutes) during competition or during designated breaks is recommended. For example, at half time in soccer or designated inter-set rest periods in tennis. References Arngrimsson SA, Petitt DS, Stueck MG, Jorgensen DK, & Cureton KJ (2004). Cooling vest worn during active warm-up improves 5-km run performance in the heat. Journal of Applied Physiology 96, 1867-1874. Byrne, C., Owen, C., Cosnefroy, A., & Lee, JK. (2011) Self-paced exercise performance in the heat after pre-exercise cold-fluid ingestion. Journal of Athletic Training, 46, 592–599 Gonzalez-Alonso J, Teller C, Andersen SL, Jensen FB, Hyldig T, & Nielsen B (1999). Influence of body temperature on the development of fatigue during prolonged exercise in the heat. Journal of Applied Physiology, 86, 1032-1039. Kay D, Taaffe DR, & Marino FE (1999). Whole-body pre-cooling and heat storage during self-paced cycling performance in warm humid conditions. Journal of Sports Science, 17, 937-944. Tyler, C.J, & Sunderland, C. (2008). Neck cooling during exercise in the heat improves subsequent treadmill time-trial performance [abstract]. Medicine & Science in Sports & Exercise, 40(5), S368.    
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