Safe Exercise in the Summer Heat

Staying cool and hydrated key to exercising during warmer months.

Sheri Colberg-Ochs By Sheri Colberg-Ochs, PhD

What's the big deal about exercising outdoors during the hotter months of the year? Besides sweating a lot, it's not a problem, right? Wrong! It can actually be deadly! Does that mean that you should give up exercising outside during the long, hot summer? Absolutely not! However, you do need to become better informed about how to safely be physically active outdoors when it's hot, even if you're just playing a round of golf.

Exercise causes you to lose fluids, and not just what you lose by sweating. You also lose fluid through your skin that you're not even aware of (called "insensible perspiration") and extra water from your heavier breathing because your expired air is humidified (which is why you can fog glass with your breath). Even before you start exercising, you may be slightly to moderately dehydrated, as dehydration is more common in people with diabetes, especially if not well controlled. When blood sugar levels are high, some of the excess glucose spills out into the urine along with extra water, which is why frequent urination is a symptom of poorly controlled diabetes (and why "diabetes mellitus" means "sweet urine").

Don't Dehydrate

According to the American Diabetes Association, proper hydration for people with diabetes is essential since dehydration can adversely affect blood glucose levels and heart function. For exercise in the heat, they recommend adequately hydrating prior to exercise by consuming 17 ounces of fluid two hours before (a mouthful is about one ounce). During exercise, fluids should be drunk early and frequently in an amount sufficient to compensate for losses in sweat or the maximal amount of fluid tolerated.
While I agree with most of the ADA's recommendations, some modifications are definitely in order. It's not that drinking plenty of fluids isn't as important as it used to be; rather, the problem is that people believe that they must stay hydrated at all costs, resulting in overhydration to the point of literally killing themselves with too much fluid. Exercisers who drink excessive fluid dilute the sodium content of their blood and cause a medical condition known as hyponatremia, or "water intoxication," which puts them at risk for mild nausea to more severe symptoms like seizures, coma, and death.

Don't Overhydrate

After years of telling exercisers to prevent dehydration at all costs, we are finally realizing that drinking too much during intense or prolonged physical activities poses a far greater health risk. An increasing number of recreational exercisers – distance runners and even hikers – are severely diluting their blood by drinking excessive amounts of fluid, with some falling gravely ill and others dying. By way of example, out of 488 runners in the 2002 Boston Marathon, 13 percent – 62 of them – drank so much that they developed some degree of water intoxication. In fact, three runners diluted their sodium levels so much that they almost died – from a recreational race! Slower paced, recreational exercisers take longer to complete activities, which gives them plenty of time to drink copious amounts of liquid – an average of three liters, or about 13 cups of fluid over that four-hour-plus marathon run – so much so that they actually gained weight during the race. Luckily, this condition is totally preventable simply with lesser fluid consumption.

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Last Modified Date: June 04, 2013

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by Lindsey Guerin
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