Seeing no risk of permanent damage, Testa gave Evans the green light. "It was a stable fracture—small but very painful," he said. "Cadel is a super-tough guy, so he managed very well. He did as much as any human could do."
"A hot environment is one of the most severe stresses an athlete can endure," says Testa, also an exercise performance physician in Salt Lake City. "Water has a high thermal capacity, so it's able to keep your temperature constant. For that reason, drinking water before, during and after exercise is more important than fuel."
Your organs and chemical reactions work only within a precise range of temperature. If you go above this ideal range and become hyperthermic (too hot), you may become dizzy, fatigued, winded. This can lead to cardiac problems, even death.
Selina Shah, M.D., a sports medicine physician at the Center for Sports Medicine at Saint Francis Memorial Hospital in San Francisco, points out that water is also necessary for proper muscle contraction and for blood flow.
"Dehydration decreases blood volume," Shah says. "Your blood thickens, forcing your heart to work harder. Blood is shunted to your brain because it's the most important, then to the muscles you are utilizing for exercise, which means less flow to your GI—your gut."
Shah notes that this may cause cramping, nausea, diarrhea, vomiting—or headaches and confusion, which, ironically, often lead to people misinterpreting their thirst as hunger.
When summer temperatures exceed your skin temperature, your body's ability to release heat is compromised. Humidity increases the challenge. When you perspire, sweat evaporates from your skin and cools your body. High humidity, however, prevents evaporation. When sweat drips off you, it's not evaporating&mdash/and not cooling your body. Thus, sweating and a flushed appearance while exercising are signs that you are mildly dehydrated. Once dehydration worsens, all those indicators stop functioning.
In hot conditions, says Testa, you can lose 2-3 liters of water per hour&mdash/almost TWICE what your stomach can absorb. Preventative hydration is key:
- Drink fluids with and between meals and before exercise, but never more than two pints at a time.
- Eat fruits and vegetables (they're 95 percent water).
- Avoid caffeinated, alcoholic and carbonated beverages.
- During summer exercise, drink 8-12 ounces every 15 to 20 minutes, less for very long-lasting activity.
- After 30 minutes, replenish electrolytes, in particular sodium, which stimulates water absorption from your small intestine.
- Drink at least 16 fluid ounces after exercise.
If you lose more than 3-4 pounds, in the future drink more water in advance, preceding exercise or during exercise. If you continue to sweat for a half-hour after exercise, this is a sign that your body is still trying to lower your core temperature, which means you became overheated and need to be more careful next time.
Shah, who works with several professional dance companies, cautions that you don't have to be riding in the Tour de France to become dehydrated. It can hit when you golf, walk, fish, sit in the sun on a boat, go to the beach on a foggy day, swim, exercise indoors without air conditioning, or couple physical activity with going in and out of air-conditioned gyms.
( Eric Heiden, M.D., a five-time Olympic gold medalist speed skater, is now an orthopedic surgeon in Utah. He co-authored "Faster, Better, Stronger: Your Fitness Bible" (HarperCollins) with exercise performance physician Max Testa, M.D., and DeAnne Musolf. Visit www.fasterbetterstronger.com.)