Creatine. Computer model of the molecular structure of the amino acid creatine. The molecule comprises spiralling alpha helices and flat beta sheets. Creatine acts as an energy store for the contraction of muscle. From its phosphorylated form it regenerates ATP, muscle's main source of energy. It is used mostly during high-intensity short-duration exercise. 95 per cent of the body's creatine is found in the skeletal muscles, while the rest is found in the kidneys, the brain and sperm cells. Creatine can be obtained from the diet, from meat and some fish, but is also synthesised by the kidneys, liver and pancreas.