Expert Advise: Staying Cool and Hydrated Key to Exercise

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By : dLife Editors

By Sheri Colberg-Ochs, Ph.D. Updated by dLife Editors 10/23/19.

What’s the big deal about exercising outdoors during the warm summer months, or even during the fall, which in many places of the country, is unseasonably warm?

Besides sweating a lot, it’s not a problem, right? Wrong! It can actually lead to many serious problems.

Does that mean that you should give up exercising outside during the long, hot summer or even the warm fall?

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 slight 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 an 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.

So, how do you know how much fluid is enough?

A good rule of thumb is to drink during activities only when you feel thirsty.  The only exception would be for people with poorly-controlled diabetes since recent studies have shown that they may have an elevated thirst threshold (meaning that they don’t feel thirsty when they should), even when dehydrated; in that case, start drinking when you have sweated some.

You should never gain weight during physical activity; in fact, you should be sweating and actually losing some weight (albeit temporarily).

To know how much of this lost fluid to replace, weigh yourself before and after prolonged activity, and only replace that amount (1 liter of water weighs 1 kilogram or 2.2 pounds).  If you have consumed a lot of fluid during an activity, wait until you start to urinate before drinking any more.

What to Drink

As for whether you should drink water, sports drinks, or other fluids to rehydrate, it depends on your needs.

For shorter activities (lasting an hour or less), plain water is fine, unless you need some extra carbohydrate to prevent low blood sugar. Sports drinks like Gatorade or PowerAde can be used, but watch carbohydrate intake (as most contain 6 to 9 grams of carbs per 8 ounces).

Don’t worry about replacing electrolytes, like sodium, potassium, and chloride, unless you are exercising outdoors in hot weather for more than two hours at a time; even then, it’s fine to wait to replace electrolytes naturally with your food later on.

If you prefer your fluids with some flavor, try flavored waters, calorie-free sports drinks (such as Champion Lyte), or Crystal Light (you can add a little salt to make it more like a sports drink).

If you need to rehydrate and treat a low blood sugar, try a regular sports drink, sugary soda, or diluted fruit juice.

Staying Cool

To avoid overheating, try exercising at a cooler time of day.  Ten to two o’clock offer the sun’s most direct rays, and you will gain more heat simply from its radiant energy.

If you can’t avoid the sun, wear white or light-colored clothing that reflects more rays, and always wear a shirt as your skin (regardless of its color) absorbs more radiant energy than light-colored clothing.

Wear loose-fitting clothes that allow air to circulate between the material and your skin.

Most importantly, if you ever start feeling too hot or experience any other symptoms of heat stress – such as nausea, dizziness, extreme thirst, or disorientation – find a place to sit down out of the sun (in some shade or indoors), drink some cool fluids, place ice around your neck, or consider wetting yourself down with cool water to cool off.

While mild heat stress will pass, heatstroke is a serious medical emergency requiring immediate action to cool your body down to prevent coma or death.

Finally, give yourself about two weeks to fully adjust to exercising in the heat. Start out by exercising outdoors at cooler times of the day and at a lower intensity.

Once acclimatized, your body will actually sweat sooner and more than before, allowing you to cool down more effectively.  If you don’t like to sweat, then your best bet is to find a nice place to exercise indoors in the air conditioning!

NOTE: The information is not intended to be a replacement or substitute for consultation with a qualified medical professional or for professional medical advice related to diabetes or another medical condition. Please contact your physician or medical professional with any questions and concerns about your medical condition.