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
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!