drink, don't dry

Fifty-Plus Fitness Library

Drink, Don’t Dry

Sharon Bortz, M.S., R.D.

When we think about the summer temperatures in Ukiah we can almost feel the beads of sweat forming on our foreheads. Enjoying an iced tea in the shade is an easy way to stay hydrated, but when you add exercise to the picture, meeting your fluid needs takes a little more effort. For example, studies have shown that individuals exercising in the heat who are given water ad libitum replace only about two thirds of their fluid losses. In other words, exercise blunts the thirst mechanism. To add insult to injury, as we age, our thirst drive diminishes. A common consequence of dehydration is decreased intensity and endurance of exercise performance. To scare you even more, a mere 2% loss of body weight by dehydration can impair the body’s ability to dissipate heat, and a 4% loss can cause heat exhaustion or even life-threatening heat stroke.

The primary cause of dehydration during exercise is an increase in sweat production along with inadequate fluid replacement. What can you do to prevent dehydration during exercise? It’s actually easier than you think; know how much you sweat during exercise, then know how much fluid to drink to replace it. For you dehydra-phobics (that should be all of us!), use these guidelines:

Prepare squeeze bottles containing a known volume of fluid to ingest during your typical training session
Weigh yourself just before exercising (without clothes)
Train for your usual time in typical clothing and environmental conditions
Ingest water/sports drink from prepared squeeze bottles to prevent significant dehydration
After exercising, dry off and weigh yourself again without clothes
Calculate your sweat rate as follows:

Body weight before training: 170 lbs
Minus body weight after training: - 169 lbs
Plus weight fluid ingested: + 1 lb (16 oz or 2 cups)
2 lb lost sweat

2lbs Fluid = 2 x 16 = 32 oz (4 cups) fluid lost

Replace at least 80% of sweat loss before, during, and right after exercise. This example requires at least four 6-ounce bottles of fluid.

Use these guidelines to prevent dehydration during exercise:

Drink plenty of water or sports drinks before, during, and after exercise.
Don’t wait until you are thirsty to drink. Thirst is a symptom of dehydration.
Drink cool beverages.
Begin replacing fluid losses immediately after exercise for quickest recovery.
Closely supervise children participating in sports or other activities. Make sure they have scheduled fluid breaks.
Common early symptoms of dehydration:
thirst
dark urine
increased heart rate
increased blood pressure
headache
heat cramps

Sharon Stewart Bortz, M.S., R.D., is a nutritionist formerly with the Stanford Center for Research in Disease Prevention and Tufts University. She also was recent co-author on Diabetes and Weight Loss.