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.”
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.
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 walking.
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 activity.
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!