Ty Downing

AS RECENTLY AS 1992, RECOVERY was a small, unexciting topic having to do mainly with rest, massage, and stretching. Most athletes understood, at least vaguely, that exercise robbed them of fluids and fuel. But there was little consensus on a dietary response, and the available products were limited to either sugary cocktails or "protein shakes for muscleheads," as Burke says.

Working with U.S. cycling team members who were complaining of overtraining and fatigue, Burke suspected that his weary athletes were suffering from something called chronic glycogen depletion. When you eat a starchy food like a banana or chug a sports drink, the carbohydrates get converted into blood sugar, or glucose, which muscles burn for energy. But any glucose not burned immediately gets stored in the liver and muscles as glycogen, which can be converted to energy later. Glycogen is, in fact, the body's preferred fuel during exercise. It's far easier to burn than fat and more readily available to the muscles than blood glucose. When you run out of glycogen during exercise, the body turns to blood glucose, which is almost impossible to maintain during training or competition. And you bonk. Worse, your body gets so desperate to maintain blood-glucose levels that it converts precious muscle protein into fuel as an emergency substitute. In short, glycogen is gold, especially to endurance athletes.

But glycogen replenishment is a tricky process. You can't start replacing it while exercising, because any carbs consumed are immediately burned by the muscles. Nor, more important, can you wait too long after exercise. According to research done in the 1980s by John Ivy, an exercise physiologist at the University of Texas (and another Ball State alum), athletes have a 60-minute post-exercise window in which muscles are primed to refuel. During this period, your muscles will convert carbs into glycogen up to three times faster than at other times. But miss it, and no matter how much pasta you eat later at dinner, more of the calories will end up as fat, or simply be eliminated as waste.

In the early 1990s, Ivy, who spent as much time in the lab as Burke did with athletes in the field, discovered that it was possible to open the window a little wider. Ordinarily, even super-receptive muscles convert only a small fraction of available carbohydrates into glycogen. Anything above a certain threshold—about 1.2 grams of carbs per kilogram of body weight—is effectively turned into fat. So Ivy tried a different approach. He knew the key to glycogen replenishment is the hormone insulin, which helps transfer glucose into the muscles and convert it into muscle glycogen. Aware that certain amino acids stimulate insulin production, Ivy added about a gram of amino-rich protein to every three to five grams of carbohydrates in his athletes' post-exercise meal. And lo! Glycogen synthesis jumped by 30 percent. In the realm of sports medicine, says Ivy, "it was a pretty big deal."