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HEAT

ACCLIMATIZATION AND TEAM

SPORTS

KIMBERLY BOWMAN MSc Candidate, University of British Columbia Canadian Sport Institute Pacific Sport Physiologist Intern

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any elite team sport athletes face the physiological challenge of having to compete in extremely hot weather conditions [4]. Exercising in the heat induces a large stress on the body’s cardiovascular and thermoregulatory system, as metabolic heat generated from intense exercise is coupled with environmental heat [11]. Soccer in particular is a physically demanding sport requiring technical skill, strong endurance, and repeated sprint ability [3,11-12]. Mohr and colleagues (2010) highlighted the impact of an added thermal load when observing soccer match performance in a hot condition (~40˚C) compared to that in mild weather (~21˚C). Specifically, reductions in total distance (-7%), high intensity running (-26%), and running velocity (-3%) [11].

Benefits of Heat Acclimatization Heat acclimatization (HA) involves exercising at a target core temperature stimulus (~38.5˚C) in a hot environmental condition over 1-2 weeks [9]. Repeated heat exposures allow adaptations to develop that attenuate the negative effect of heat stress through improvements in exercise capacity and perceptions of thermal load [4]. More recent studies have shown heat acclimatization to be ergogenic in both mild and hot conditions, therefore, cold weather sports may also benefit from utilizing a heat protocol prior to competition [10]. The magnitude of heat adaptation is determined by: intensity, duration, frequency, number of heat exposures, and environmental condition [4, 9].

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Performance Tests and Monitoring Metrics in Heat Athletes performing at high intensities in Acclimatization Thermoregulatory & cardiovascular adaptation

competitive games commonly have sweat rates ≥2.5L/h [16]. Heat acclimatization improves thermoregulatory efficiency via a lowered sweating threshold and a reduction in the core temperature threshold for sweating (~0.15 to 0.29˚C) [4]. Acute acclimatization regimes have also reported a greater cardiovascular stability while exercising in the heat via a plasma volume increase (3-27%) [9].

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Telemetric heart rate (HR) chest monitors (Polar Electro) used to monitor HR response act as an indirect assessment for change in cardiac efficiency, aerobic capacity, and training intensity [1]. Common HR metrics include i) Exercise HR (HRex): the mean HR in the final 30sec of the 5-minute running period and ii) Recovery HR (HRR): the mean drop in HR over a 1-minute rest period post-run [1-2]. Additionally, a GPSaccelerometer (Global Positioning System, Catapult Minimax S4) can be used to track soccer-specific external load metrics in real-time [11, 18]. The S4-GPS device can monitor; total distance covered, meters per minute (m/min), number of high-speed runs (>16.5km/h), and high IMA or accelerations/

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