Food During Exercise? Guidelines for Avoiding Fatigue

Fatigue during a workout or sporting event is usually caused by lack of water, salt or sugar. Most athletes in sports that last more than a couple of hours know that they should drink and take in some salt, but they also need a source of sugar.

When you exercise, you get your energy from sugar and fat stored in your muscles and sugar and fat in your bloodstream, and, to a lesser extent, from protein. At first you get more than 80 percent of your energy from fat and sugar stored in muscles. Usually at the start of exercise, almost 45 percent of the energy comes from stored muscle sugar. As you continue to exercise, you use up fat and sugar stored in muscles and get far less from these stores. After two hours of exercise, you have used up most of your stored muscle sugar (glycogen) and get less than 15 percent of your energy from that source. At four hours, your muscles have almost no stored sugar at all.

When your muscles are depleted of their stored sugar, they become difficult to coordinate and feel heavy and hurt. Your muscles can get some sugar from gluconeogenesis, a process in which your liver makes sugar from protein (branched chain amino acids), but that is not enough for all-out exercise. During intense exercise, you need a source of sugar. It can come from sugared drinks or any carbohydrate-rich foods. You can use special sugared exercise drinks, sugar gels, carbonated soft drinks, exercise bars or any food that contains sugar or flour. Fitness newsletter