Creatine, or creatine monohydrate, is a naturally occurring amino acid that helps skeletal muscles produce ATP (adenosine triphosphate, the body's energy molecule) and volumises or increases muscle mass via hydration. When you do high-intensity, short-duration exercise, such as lifting weights or sprinting, a chemical reaction takes place, providing a burst of energy to your muscles. Creatine is fundamental to this reaction. Your body does not store very much creatine in your muscles for normal, everyday functions. Creatine supplementation has been widely shown to increase fat-free weight and muscle strength, improve endurance, and delay fatigue for high-intensity, short-duration sports. It does not aid endurance or aerobic sports such as running or cycling.