A hot environment is one of the most severe stresses an athlete can endure, according to Dr. Eric Heiden, an orthopedic surgeon and five-time Olympic gold medalist speed skater writing for the Chicago Tribune.
Water has a high thermal capacity, so it’s able to keep body 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.
Water is also necessary for proper muscle contraction and blood flow.
Dehydration decreases blood volume. Blood thickens, forcing your heart to work harder. Blood is shunted to the brain because it’s the most important, then to the muscles you are using for exercise, which means less flow to your stomach.
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 — 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, you can lose 2 to 3 liters of water per hour — almost twice what your stomach can absorb. Preventive hydration is key, such as:
• 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.