Good for Workouts of 90 Minutes or More : Sports Drinks Not Always Helpful

Jane rides an exercise bike three times a week for half an hour at a time. Hillary takes aerobic dance, a 1-hour class, four evenings weekly. Kate is training for a marathon; she runs 6 days a week, 45 to 90 minutes at a stretch.

All three toss down sports drinks during and after their workouts, but only one of them really needs to.

Sports drinks won’t hurt any of these exercisers, but they won’t make a difference in health or performance either, unless exercise goes on 90 minutes or longer. (Kate, therefore, is probably wise to sip a sports drink during and after her longer workouts.) The fluids, which are widely available in supermarkets, drugstores, sporting-goods and health-food outlets and through mail order, contain water, sugar, salt and added flavoring.

Water is the most crucial of these ingredients. Without it, the body overheats--a process that can start within minutes of exercising on a hot, humid day, and if not reversed can lead to heatstroke, with symptoms of muscle cramps, headache, disorientation, loss of consciousness and, in extreme cases, death.

The solution is to drink enough before, during and after exercise to keep fluids replenished. And if your workout is under 90 minutes, water is all you need.

Why sports drinks, then, for longer workouts? Carbohydrates are the primary reason: Your exercising body runs on them like a car runs on gas. They are stored in the muscles and liver as glycogen and circulate in the bloodstream as blood sugar (glucose).

During exercise the body burns glycogen first; when that runs out, blood sugar becomes the main energy source. After about 90 minutes, the blood-sugar supply reaches a point where noticeable fatigue sets in. Sports drinks counter that effect by supplying a steady source of carbohydrates to working muscles. Blood-sugar levels stay steady, and you don’t feel tired.

The catch: Too much sugar can slow you down. Sports drinks (or any sugary solution, such as fruit juice or soda) that are too concentrated can build up in the stomach and slow “gastric emptying”--the passage of fluid and glucose from the stomach to the small intestine, where they are then absorbed into the bloodstream. You may also get abdominal cramps and feel nauseated.

The gastric emptying problem led scientists, until recently, to warn athletes off sports drinks altogether. It was thought that any drink with more than 2.5% carbohydrates would slow the passage of fluid to working muscles, explained J. Mark Davis, director of the Exercise Chemistry Lab at the University of South Carolina in Columbia.

But there were two problems with the 2.5% cutoff: First, beverages of that concentration didn’t provide enough sugar to boost performance anyway; and second, most solutions on the market were (and still are) at least 6%.

Some manufacturers thought they had solved the problem several years ago with “glucose polymers,” chains of about five sugar molecules. The theory was that large numbers of separate molecules stayed in the stomach longer, but if linked together, they would leave the stomach faster. However, experiments by David Costill, director of the Human Performance Lab at Ball State University in Muncie, Ind., showed that polymers don’t leave the stomach any faster than regular carbohydrate solutions.

Recent research has provided further proof that polymers are unnecessary by showing that gastric emptying isn’t really a concern with most sports drinks after all.

Davis led a study that had 19 well-trained male cyclists pedal at a moderate pace on stationary bikes for 2 hours, rest half an hour, then get back on for an intense 30-minute ride. All were given drinks every 20 minutes--some an 8% carbohydrate solution, some a 2.5% drink and some a water placebo. All three drinks contained deuterium oxide (“heavy water”), a substance that can be measured safely to show how quickly fluid travels from the mouth to the bloodstream.

All three groups performed about the same during the 2-hour workout. But in the final half hour, the 8% carbohydrate solution group performed 10% better than either of the other groups. “That’s a big difference for someone interested in winning a race,” Davis said.

Keeping tabs on the deuterium oxide showed that the 8% drink reached the bloodstream just as fast as the 2.5% solution or the water placebo. Once there, the 8% solution kept the subjects’ blood-sugar levels constant over the remainder of the study period, keeping performance at the same high level.

Sports drinks’ other main ingredients replace the sodium, potassium and chloride that you lose through perspiration. While essential for life, these elements do not contribute to performance unless you’re exercising at high intensity for several hours at a time, said Costill, who has conducted studies on sports drinks and gastric emptying that agree with Davis’ findings.

After a moderate workout, the electrolytes that you have lost can be replenished quickly and easily when you consume your first post-exercise meal, said Nancy Clark, a nutritionist at the Sports Medicine Clinic in Brookline, Mass. “An orange or a banana will give you all the potassium you need,” she said, “and if you eat any processed food--bread, frozen food, canned soup--you’ll get plenty of sodium.”

The electrolytes in sports drinks won’t hurt you--a glass of Gatorade, for example, has about as much sodium as the same amount of milk. But you shouldn’t let yourself be talked into believing your health or exercise performance will suffer if you don’t get them into your system during or after a moderate workout.

If you will be exercising for 90 minutes or longer and want to try a sports drink, here are guidelines for getting the most from every gulp:

* Consume about 8 ounces (a cup) of fluid every 20 minutes.

* Don’t drink anything with a carbohydrate concentration greater than 8%. Most sports drinks are in the 6% to 8% range--check the label and dilute if necessary.

Apple juice and most sugar-sweetened carbonated sodas contain about 12% carbohydrates; diluting them with equal amounts of water will give you the right concentration. Neither Davis nor Costill has observed a problem with cramps or nausea in exercisers using solutions of less than 8%.

* Don’t drink any carbohydrate beverage less than 20 minutes before you begin a workout. This will raise blood-sugar levels, which then drop as you start exercising, Davis said, and can make you feel lightheaded and dizzy.

The solution: Drink water before your workout, sports drinks during and after.

* If you’re training for a long-distance event--a triathlon, say--practice using sports drinks during long workouts to make sure your body tolerates them. Intolerances are rare, but you wouldn’t want an unexpected problem to force you out of the running on race day.

* If water is all that’s available and you’re thirsty, drink it. You’ll be sidelined a lot faster due to lack of water than because of a need for salt or sugar.