Glycogen is stored carbohydrate, found mainly in skeletal muscle and the liver. It is vital during intense exercise, because it provides energy more quickly than fats. Unfortunately, glycogen stores are limited and glycogen depletion leads to fatigue and an increased risk of injury.
Hamilton Roschel from the University of São Paulo in Brazil, in a study on rats, found that exercise capacity and glycogen levels were greater in animals given creatine supplements following intense intervals (repeated bouts of 30-second maximal exercise, followed by 2 minutes rest).
Other studies found similar results in humans. Creatine might be an excellent supplement for training because it allows athletes to work harder, which would result in greater fitness gains. (Journal of the International Society of Sports Nutrition, 7: 6, 2010; published online)