While sweating is necessary to help cool the body, the production of sweat comes at the expense of your body fluids. As much as 1 to 2 quarts of fluid per hour may be lost as sweat while cycling in very hot weather. To help you understand the seriousness of this, the loss of as little as 2 to 3 percent of your body weight due to dehydration can impair exercise performance.
Therefore, to help maintain adequate hydration and prevent heat illness during prolonged cycling in the heat, it is vital that you acclimatize and that you replace fluids lost through sweating.
Keeping Your Cool
Here are a few suggestions for preventing heat stress and adapting your program to the demands of summer training or competition.
When the first hot spell of summer hits, gradually work your way up to several hours of exercise in the heat during your first few training sessions. A gradual build-up in distance and intensity should be completed by the seventh to 10th day of training.
But everyone adapts differently to heat stress. In order to help your own body adjust, make sure you adapt gradually to a hot environment.
Time of day is crucial. While you may have acclimatized to conditions in the morning, you still need to take steps if you are going to race during the heat of the day, when the heat is highest (noon to 3 p.m.). Over the last few days before an event, make a point of riding at that time of day to enhance your adaptive training. If you can only train in the morning, then wear extra clothing to purposely increase the heat stress.
As stated earlier, during hard training you will lose 1 to 2 quarts of fluid through perspiration each hour. If your fluid loss by sweat or urine exceeds your fluid intake, you will experience dehydration.
More: Cycling Hydration Myths
Body weight losses in the 3 to 4 percent range impair the body's ability to efficiently utilize oxygen. When dehydration causes more than 4 to 5 percent weight loss, your power will deteriorate tremendously. Always be aware that even during non-athletic activities, in hot and humid conditions your fluid losses will typically range from 1 to 10 quarts every 24 hours.