Dr. Jose Antonio, PhD and CEO of the International Society of Sports Nutrition says, "The most common mistake is to consume just plain water; during a training run/bike/paddle that exceeds 75 minutes. It's best to consume a sports drink. Especially one that contains a modicum of protein." In order to prevent your body from eating your own muscle for energy, you need to fuel properly. "Work by Mike Saunders has shown that carbohydrate-protein ingestion improves endurance performance to a greater extent than carbohydrate alone. This applies not just during 'normal' environmental conditions but also in the heat. ". It has been a long held myth that protein (in a sports drink) dehydrates you; on the contrary, performance is likely enhanced and recovery is expedited."
More: Protein: Pros, Cons and Confusion
Of course, choosing the time of day you work out will make a big difference in the amount of heat you create and how much fluid you use. It's wise to train in the mornings or evenings during the warmer months, rather than in the middle of the day when the temperatures are the warmest.
Also choosing appropriate clothing is essential. Contrary to old-school work out myths, wearing long sleeves in the heat only causes dehydration. Dry-fit style clothing will help wick moisture from your skin, aiding in the cooling process. It also dries fast, allowing you to stay cool.
More: 8 Tips for Exercising in Summer Heat
Caffeine and Alcohol
The Institute of Medicine
, 2004, p.S-5 (the IOM report) also addresses the use of alcoholic and caffeinated beverages. "While consumption of beverages containing caffeine and alcohol have been shown in some studies to have diuretic effects, available information indicates that this may be transient in nature, and that such beverages can contribute to total water intake and thus can be used in meeting recommendations for dietary intake of total water".
What does this mean for the athlete? In brief, it means that the periodic ingestion of beverages containing caffeine and alcohol probably will not compromise hydration status. However, common sense dictates that such drinks should not be ingested at times when the effects of caffeine and alcohol on stimulating excess water loss in the urine could compromise hydration status. Thus, beverages containing caffeine or alcohol should be avoided before or after heavy training, when maintaining and restoring hydration status is important.
More: The Facts About Caffeine and Athletic Performance
Plain water then, although a good thirst quencher, is a poor rehydrator. As opposed to a sports drink that helps maintain the physiological drive to drink, water shuts off thirst before an athlete can properly rehydrate. Unfortunately, when athletes drink only water, the osmotic drive to drink is removed because plasma blood sodium level—the primary determinant of plasma osmolality—is quickly lowered below the thirst threshold. Ingesting water can alleviate thirst when hydration status is not even close to normal.
More: How Much Water Should You Drink?