Dehydration Causes Cramps
Although pro cyclists routinely become dehydrated during races we rarely read about cramps in the peloton. In lab experiments, dehydration does not cause cramps.
Drink Early and Drink Often
In the mistaken belief that dehydration affects performance and causes cramps, we are taught to drink before a workout and to continue drinking frequently during the workout. Develop the habit of drinking enough throughout the day so that you are fully hydrated—you urinate every few hours with good output. Don't force yourself to drink on the bike.
Drink Before You're Thirsty
We're also told to drink before we're thirsty to be sure we take in enough fluid. Sports scientists now recommend drinking just enough to satisfy thirst in order to avoid hyponatremia. Your body is marvelously effective at self-regulating. If you become significantly dehydrated, your thirst mechanism will kick in.
Water Is All You Really Need
Taste your sweat—does it taste like clear water? No! In addition to replacing the water you lose in sweat, you need to replace the sodium. A liter of sweat contains about 800 mg of sodium—half the recommended daily intake of sodium. So after a sweaty workout, don't spare the saltshaker. A quart of your sweat contains 115 mg of potassium, only about 2.5 percent of the recommended daily intake of potassium.
Sports Drinks Provide the Necessary Electrolytes
Yes, but only to an extent. The American College of Sports Medicine recommends that a sports drink contain 125 to 175 mg of sodium per 8 fluid ounces and 20 to 48 mg of potassium per 8 fluid ounces. Most sports drinks don't provide nearly enough sodium, the one electrolyte you really need to replace. If they had enough sodium they'd taste terrible. Read the ingredients on the label of your sports drinks.
Electrolyte Depletion Causes Cramps
If you cramp, you may have been told to eat a banana for potassium, take Tums for the calcium or a supplement for magnesium. The amount of each of these electrolytes in sweat is minute compared to what your body stores, and depletion doesn't cause cramps. Experts continue to disagree as to whether sodium depletion causes cramps or not.