How to Avoid Heat and Dehydration

Avoiding heat stroke, heat exhaustion, and dehydration is crucial for those

exercising in hot weather, says W. Larry Kenney, Ph.D., FACSM. He also

speculated that hot-weather risks may increase even more in the future.

"Right now, it's difficult

to tell from available data if global warming and climate changes have played a

role in increasing heat-related injuries during the past few years," Kenney

said. "But global warming can increase the frequency and intensity of heat

waves, which, of course, can lead more heat illness casualties."

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Kenney was careful to

dispute recent studies claiming that (1) dehydration of 2 to 4 percent body

weight loss does not impact exercise performance, and (2) body weight loss is

not a good way to monitor the body's fluid needs. Instead, he encouraged

athletes to monitor their pre- and post-exercise weight in order to maintain

proper hydration. According to Kenney athletes should:

1. Calculate their body's

sweat rate (by adding weight lost in one hour of exercise plus amount of fluid

consumed during the hour of exercise). Athletes should aim to replace all fluid

lost during exercise, and rely on sweat loss, rather than just thirst, to

monitor fluid needs.

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2. Drink fluids before

exercise and periodically during exercise, instead of practicing rapid fluid

replacement in the middle of exercise. Drinking at intervals will provide more

adequate hydration and urine production.

3. Avoid extreme excessive

water consumption, which can lead to hyponatremia (over-hydration that may

dangerously reduce sodium concentrations in the body), in rare cases.

Kenney also explained the

physiological differences between heat stroke and heat exhaustion. "During heat stroke, the body

essentially shuts down its mechanisms for heat release, including sweating," he

said. "Heat exhaustion, however, is basically severe dehydration that affects

the cardiovascular system. Fluid is lost from all body compartments, including

the blood, forcing the heart to work harder to maintain output." Warning signs of heat illness and

dehydration include thirst, irritability, headache, dizziness, muscle cramping,

unusual fatigue, nausea, vomiting, hyperventilation, and confusion or problems


Remember heat illnesses are

categorized as exercise-associated muscle cramping, heat exhaustion, and

exertional heatstroke (EHS). All conditions must be monitored in order to

avoid withdrawal from activity or, at worst, collapse during or soon after


EHS is the most serious of

the range of heat illnesses, and may ultimately result in death. Early

recognition and rapid cooling can reduce that risk. The guidelines

recommend that coaches, medical personnel, and athletes have a high level of

awareness and monitor at-risk athletes closely to recognize subtle changes that

may occur with the development of EHS.

EHS occurs most frequently

in hot humid conditions but can occur in relatively mild temperatures with

varying levels of humidity.

A rectal temperature must be

measured as it demonstrates the only discernable difference between severe heat

exhaustion and EHS in on-site evaluations.

Rapid cooling in an ice

water tub or rapidly rotating ice-water soaked towels will decrease the chance

of dying from EHS.

EHS can occur more

frequently in short, fast-paced road races than in slower-paced marathons

"Prevention is the key to reducing the risks associated with heat

illnesses," said William O. Roberts, M.D., FACSM, ACSM past-president and

member of the writing committee. "The guidelines are important for

every runner – fast or slow – and every outdoor athlete – training or competing

– to understand in order to recognize and treat a heat-related condition."

Something to think about as

the thermometer climbs!

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