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revised July 26, 2007

Heat and Humidity

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High intensity exercise in a hot environment, with the associated fluid loss and elevation of body temperature, can lead to dehydration, heat exhaustion and heat stroke.


Fluid loss occurs during exercise, mainly due to perspiration and respiration (breathing). Fluid loss makes an athlete more susceptible to fatigue and muscle cramps. Inadequate fluid replacement before, during and after exercise will lead to excessive dehydration and may lead to heat exhaustion and heat stroke.

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Signs of heat exhaustion for the athlete:

  • High heart rate, dizziness, headache, loss of endurance/skills, confusion and nausea
  • Skin may still be cool/sweating, but the athlete may be pale
  • Cramps may be associated with dehydration (muscular, abdominal)
  • Athletes will pass little urine; urine will be highly concentrated
  • Rectal temperature may be up to 40 degrees Celsius and the athlete may collapse upon stopping an activity

Signs of heat stroke for the athlete:

  • This is a potentially fatal condition and must be treated immediately by a medical professional
  • Heat stroke is similar to heat exhaustion, but with dry skin, confusion and collapse
  • Heat stroke may arise in an athlete who has not complained about symptoms of heat exhaustion and has continued to be active

How to prepare for competition in hot conditions:

Preparation for exercise under hot conditions should include a period of acclimatization to (or "getting used to") those conditions, especially if the athlete is traveling from a cool/temperate climate to compete under hot/humid conditions.

Regular exercise in hot conditions will help the athlete adapt to those conditions, and will help prevent the athlete's performance from deteriorating (to heat illness) during later competitions. A period of seven to 10 days of 60 minutes acclimatization activity each day (under hot conditions) provides substantial preparation for safe competition in the heat.

Source: SmartPlay: "Heat Guidelines"

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Revised: July 26, 2007


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