MEDICal issues
heat stress and tennis performance – Written by Julien D. Périard, Qatar
Extremely hot conditions took over Rod Laver Arena and the rest of the tennis grounds in Melbourne Park during the 2014 Australian Open. After days of sweltering hot weather and temperatures reaching 43ºC, play was suspended for several hours when organisers invoked the Extreme Heat Policy. The stoppage in play, however, occurred only after a plastic bottle had reportedly started melting on court, a ball boy and a male player fainted, a female player experienced cramping and vomiting, and several notable players expressed their concerns regarding the safety of continuing to compete in such conditions. Unfortunately, the sequence of events that played out on the international stage in Australia is mirrored worldwide each year in numerous lower-profile events, highlighting the challenges and consequences of competing under severe heat stress. In effect, the development of hyperthermia during exercise in the heat has been shown to impair endurance1 and intermittent exercise performance (e.g.
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soccer)2,3. These performance impairments occur in conjunction with elevations in physiological and perceptual strain, relative to when exercise is performed in cooler conditions. During the development of hyperthermia, progressive dehydration can also occur if fluids are not sufficiently consumed, which can in turn exacerbate the rise in thermal strain. Tennis is a high-intensity, long-duration intermittent activity4 with work periods performed at 60 to 75% of maximal oxygen uptake interspersed with periods of light activity or rest5. The cumulative effect of these high-intensity repetitive efforts over several hours has a detrimental influence on performance through the development of fatigue4,6. This fatigue, described as a time-dependent exerciseinduced decrement in the capacity to produce maximal force or power, has important implications for several performance aspects such as sprinting, jumping and force production. This brief review will examine the role of heat
stress and hydration on match-play tennis performance and thermoregulation. MATCH-PLAY TENNIS, HEAT STRESS AND THERMOREGULATION The rise in body core temperature during exercise is mediated by relative intensity/ workload and the prevailing environmental conditions. In conditions within the prescriptive zone – ambient temperatures in which deep body core temperature remains stable during exercise7 – core temperature increases safely up to 38.3°C during match-play tennis8-10. This suggests that in temperate environments, both autonomic (e.g. sweating) and behavioural (e.g. adjustments in play and recovery) thermoregulation successfully regulate core temperature. However, in hot ambient conditions core temperatures above 39.5ºC have been reported during play8,11-13. The development of this thermal strain, along with the concomitant increase in physiological and perceptual strain (Figures 1 and 2), is characterised by a
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Thermal comfort
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Figure 1: Rectal temperature, thigh skin temperature and heart rate during 20 minutes of effective match-play tennis (2 × 10 minutes) in COOL and HOT conditions. *Significantly different from COOL, P
