By Cindy Carroll
As the weather heats up, those of us exercising or working outdoors can maximize our performance simply by gauging how much we sweat.
UT Chattanooga professor Brendon McDermott specializes in how to prevent heat-related deaths, particularly among athletes. But even for casual exercisers, he has some educated advice about staying hydrated and avoiding heat illness. McDermott is assistant professor, clinical coordinator for the Graduate Athletic Training Program, and codirector of the Applied Physiology Laboratory at UTC.
He says if those half-marathon days of high school are long behind you, there are still a few things to consider before sizzling on a jogging track in the summer heat. Hydration guidelines have evolved for the average person, but who exactly is the average person? Each body reacts differently, and replenishment needs depend upon the individual, according to McDermott.
“Sweat rate is very simple to calculate: weigh yourself before exercise, with as little clothing as possible; exercise for a half an hour and don’t drink or use the bathroom for that half hour; weigh yourself again, wearing the same amount of clothing to see how much you’ve lost,” McDermott says.
To get a true picture of sweat rate, this test should be done in the cold, in the heat, and at different intensities of exercise. It will then be easier to gauge whether you are a heavy or light sweater, and you will learn a lot about your sweat production.
If that sounds like a lot of work, there’s a quicker way to assess hydration needs, and it’s focused on the delicate matter of, ahem, passing a different kind of liquid.
“You can monitor your urine color,” McDermott says. “It should have a light yellow tinge to it—more like the color of lemonade than apple juice. It’s normal to have darker urine in the morning.”
McDermott says body size isn’t predictive of sweat production. Olympic marathoner Alberto Salazar, who weighed roughly 145 pounds, was known to lose nearly ten pounds of water an hour during training.
“When you’re talking about a football lineman who loses ten pounds of water, that may not be so bad, but for someone who is 145 pounds, that’s a huge percentage,” McDermott says. “If someone is losing ten pounds of water per hour, and they are told to replenish with sixteen ounces of water, that’s insufficient.”
Water is not enough to replenish what some athletes lose in sodium and calories, so many reach for sports drinks. But does everyone who exercises need to guzzle a beverage high in sodium and calories? “For the desk jockey who does fifteen minutes of exercise before work each morning, absolutely not,” McDermott cautions.
It’s important for everyone to be well hydrated before exercise begins, but too much water could lead to hyponatremia, a disorder involving low levels of sodium in the blood. McDermott says marathon runners, who’re urged to take in lots of fluids to avoid dehydration, sometimes overdo.
“There have been cases where people have gained up to twelve pounds [from excessive hydration] during a marathon.”
Don’t wait to drink until you notice you are parched, McDermott says, because the thirst mechanism doesn’t kick in until a person is about 2 percent dehydrated.
“It’s okay if you’re a healthy person who’s used to working out in the summertime,” McDermott advises. “But if you’re a competitive athlete, you’d be behind the game and trying to play catch up. Think again about Alberto Salazar. If he drank to thirst, he’s 2 percent behind, plus he must replace ten pounds an hour.”
Besides his responsibilities at UT Chattanooga, McDermott serves on the medical and science advisory board of the Korey Stringer Institute, founded by Kelci Stringer to “minimize sudden death in sport for any reason, beginning with exertional heat stroke.” Kelci’s husband, Korey Stringer, a Minnesota Vikings offensive lineman, died from exertional heat stroke in 2001.
Calculate your sweat rate
• Weigh yourself before exercise, wearing as little clothing as possible.
• Exercise for half an hour, and don’t drink or use the bathroom.
• Weigh yourself again, wearing the same amount of clothing to see how much you’ve lost.
• Multiply the difference in body weight by two for a sweat rate per hour.
What causes cramping?
Brendon McDermott’s current study focuses on -student athletes who cramp during intense movement. There are two prevailing theories about the cause of cramps:
• Some researchers think an electrolyte imbalance helps to initiate a cramp.
• Other researchers blame neuromuscular fatigue.
By measuring the sweat and salt outputs of students who cramp compared with a control group of students who don’t, matching the groups for factors like age, weight, and similar levels of activity, McDermott hopes to help unravel this painful mystery.