To combat this, begin drinking even before you get on the bike. Drink 8 ounces as you are getting out the door. During your ride, try to drink at least 8 to 12 ounces by sipping fluids every 20 minutes (make sure you sip, not gulp, to avoid stomach discomfort).
If you cannot carry enough fluids in your water bottles, wear a back or hip-mounted hydration system to ensure you drink enough. Such systems also keep fluids colder, and cool drinks tend to taste better, so you are apt to drink more.
There is evidence that after-exercise carbohydrate-electrolyte beverages replace lost fluid in the blood at a slightly faster rate than pure water.
To make sure that you are properly hydrated, weigh yourself before and after hard training sessions in the heat. If you finish a training session with a weight loss of more than 3 to 4 percent, you should practice drinking more while on the bike.
You can assess the status of your body's fluid level by the volume of urine expelled. An adult's urine volume is about 1.2 quarts every 24 hours. If your daily urine volume is less than 1 quart a day, your body is conserving water and you should consume more fluids.
Urine that is dark and yellow also indicates you may be dehydrated, and that your body's cells are being put under undue stress. If you experience frequent cramps, have your salt intake evaluated by a sports medicine physician or dietitian.
Keeping track of your body weight on a daily basis is an effective way to determine water loss. When you get out of bed in the morning, step on a scale. Record your weight in your training diary. If you experience a weight loss of 1 to 3 percent from the previous day's activity, avoid beginning a training session or competition until you are rehydrated. Do this by drinking 16 ounces of fluid for each pound of body weight lost.
Lastly, wear a white or light-colored jersey to reflect radiant heat as much as possible. Wear clothing incorporating new materials that allow for greater transport of air and moisture to flow in, out and over your hot body. Do not use oil-based sunscreens, which impede sweating.
Training, acclimatization and the proper use of sport drinks will help you perform your best in summer heat. The bottom line on all of this is to know your body and take care of it.
If you use common sense and prepare properly for competition in the heat, nothing should stand between you and an excellent finish. Remember, you can't change the weather, but with a little planning, you can beat the heat.