If you can work out a way to boost your muscle glycogen to supra-normal levels, your performances in athletic events lasting longer than about 60 minutes will be much improved. Glycogen is a key fuel during such exertions, but a basic problem is that, unlike fat, glycogen cannot be stored in your body in relatively limitless amounts. In addition, the glycogen in your muscles is quite rapidly depleted during fairly intense exercise, so that muscles begin to notice a shortage of glycogen after 60-90 minutes of activity. Yes, they can call on fat to provide fuel for further contractions and force production, but fat supports a lower intensity of exercise, and thus movement speed drops. This is why athletes who do a poor job of muscular glycogen replenishment before lengthy workouts, games or races usually slow down after 60 minutes, while their glycogen-loaded counterparts continue to work at the same intensity. So, the key question is: how do you make sure that you are amply glycogen-loaded? Once it became clear in the 1960s that glycogen was especially important during exercise lasting longer than an hour, Swedish scientists began to work at a furious pace to answer this question. A Swede named Ahlborg developed a protocol in which athletes performed a bout of very strenuous exercise and then consumed a high-carbohydrate diet for a period of three days while training normally (1). It worked! Athletes in the Ahlborg study boosted muscle glycogen above 150 mmol.kg-1 wet weight (‘normal’ levels are about 80-120).