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By Jill McVey DPT, ATC

Here in the Pacific Northwest, we are lucky to have easy access to hiking, swimming, paddle boarding, running, and more. As the weather continues to improve, more of us will spend our free time outdoors. Don’t let the usually temperate weather here fool you—heat illness is a very real consequence of exercise in even a slightly warm environment. Prolonged exercise with consistent sweat loss leads to progressive dehydration, which can impair physical performance. Without adequate fluid replacement, the core body temperature will continue to rise, and dehydration can induce failure of the body’s temperature regulation systems. Various heat related illnesses can result as the core body temperature rises, which can lead to a medical emergency.

Individuals with large muscle mass or those who are overweight are particularly prone to heat illness, because metabolic heat is produced proportionately to surface area. Women are more physiologically efficient in body temperature regulation than men are. Others who are susceptible to heat illness include those with relatively poor fitness levels and those with a history of heat illness.

Gradual acclimatization is the single most effective method of avoiding heat illness. Acclimatization should involve not only becoming accustomed to heat but also becoming acclimatized to exercising in hot temperatures. Progressive exposure to a warmer climate should occur over a seven- to ten- day period. During the first five or six days, 80% acclimatization can be achieved. Each session of exercise should be broken down into twenty minutes of work alternated with twenty minutes of rest in the shade.

Heat illness is preventable, but only by ensuring adequate hydration and acclimatization. Physical conditioning alone cannot affect one’s susceptibility to environmental stress.

Stay safe this summer and maximize your performance by staying hydrated.

The American College of Sports Medicine (ACSM) provides the following recommendations in a position statement on hydration and exercise:

  • Consume a nutritionally balanced diet and drink adequate fluids during the 24 hour period before an athletic event or exercise session.
  • Drink approximately 500 mL (about 17 ounces) of fluid about 2 hours before exercise
  • During exercise, start drinking water early and at regular intervals to consume fluids at a rate sufficient to replace all the water lost through sweating.
  • Ingested fluids should be cooler than ambient temperatures.
  • Addition of proper amounts of carbohydrates and/or electrolytes to a fluid replacement solution is recommended for exercise events of duration great than 1 hour.