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When it's too hot to trot

Will Graustein describes himself as a "fair-weather runner" who avoids exercising in brutal heat. On the other hand, he finds he competes pretty well in crummy weather, from blizzards to heat waves.

Graustein, 40, of Harwinton, is president of the Hartford Track Club. He is both a runner and running coach and knows how to adapt his exercise routine to the rising mercury: He cuts back a bit on mileage as the hot weather approaches to get acclimated, avoids midday workouts and drinks plenty of water.

"If it’s really hot -- or stormy -- I won’t run," he says. "That becomes my day off."

Regular exercise is one of the best things we can do for our health. But, as Graustein observes, sometimes it’s too hot to trot. Still, there is no reason to abandon outdoor exercise during the summer months. There are strategies for avoiding the hazards of heat, humidity and warm-weather pollution.

The jocks of summer have one big issue: coolant. Human perspiration is a usually-effective cooling system. When sweat evaporates, it carries off body heat. Lawrence E. Armstrong, a professor of environmental and exercise physiology at the University of Connecticut’s Human Performance Laboratory in Storrs, notes that in a hot, dry environment, sweat evaporation accounts for up to 90 percent of the body’s heat loss.

But the body also requires quite a bit of water to keep its cooling system running in hot weather.

On average, the body loses between 0.8 and 1.5 liters of fluid for every hour of exercise, according to Armstrong. That fluid has to be replaced immediately, which is why athletes of all kinds should drink plenty of water, and start before they exercise.

Dr. Mark Metersky, an associate professor of medicine in the pulmonary and critical care division at the University of Connecticut Health Center in Farmington, offers this warning: Don’t wait until you’re thirsty to drink. Thirst is an imperfect indicator of the body’s need for water. The body can lose plenty of fluids before a feeling of thirst kicks in.

Most of us don’t need the additional nutrients found in sports drinks, according to Armstrong, though these may be helpful for people who exercise for several hours a day over multiple days or for competitors in events that last more than an hour.

Even a well-hydrated cooling system can malfunction. Clothes that are too heavy or restrictive can actually block the flow of air over the skin that’s needed to promote sweat evaporation, says Armstrong. He suggests togs that are lightweight, porous and loose fitting.

A major cooling-system problem isn’t the heat, it’s the humidity. "If it’s humid, the evaporation doesn’t occur to the same extent," says Metersky. "You sweat more, get dehydrated, and you don’t get the cooling effect."

Overheating can have serious consequences. When body fluid loss is excessive, blood volume drops and this affects circulation and brain functioning. This is called heat exhaustion, and it is treated with fluids.

Heatstroke is more serious. The body temperature can rise to as high as 106 degrees. Shock, brain damage and even death can result. The treatment involves both fluids and cooling the body.

Not surprisingly, people in top physical shape can handle hot weather much better than weekend warriors, according to Armstrong. He says that athletes can acclimatize themselves to hot weather, but that it takes up to two weeks of moderate to strenuous daily exercise.

Most of us should simply cool it by scheduling summer exercise for early morning and evening hours. Avoiding midday workouts also safeguards the respiratory system from the worst levels of air pollutants like ozone, which are made worse by sunlight. And it saves the skin from the sun’s strongest and most damaging ultraviolet rays. "If it’s humid, the evaporation doesn’t occur to the same extent. You sweat more, get dehydrated, and you don’t get the cooling effect."

Copyright © 2014, The Baltimore Sun
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