ATP or Adenosine Tri-Phosphate is the form in which energy is stored. The human body contains only 85 g. These low reserves do not allow prolonged effort to be maintained. These stocks are exhausted in a few seconds, so they must be continuously replaced.
It can come from a source of instant energy stored in the muscles, phosphocreatine. This enables ATP to be regenerated during short, intense exertion. When exercise lasts longer, ATP comes from the Krebs cycle, meaning it is produced in the mitochondria in the cells, from oxygen and: - glycogen, storage form for glucose in the muscles and liver. - triglycerides, storage form for lipids in the muscles and adipose tissue.
alactic anaerobiosis. This is used during short intense exercise (sprint, weightlifting, jumping, throwing) that takes place without oxygen. This stream uses local phosphocreatine reserves that are used up in 10 seconds. alactic anaerobiosis This takes over from the alactic stream for short, high intensity exercise periods (a few minutes). This stream does not need oxygen to breakdown glucose but it produces lactic acid. This is the limiting factor in this system because the more it accumulates, the lower the performance. aerobic This metabolic pathway is used for prolonged or endurance exercise. Muscular contraction can be maintained because ATP is continuously regenerated. This stream requires oxygen and can breakdown carbohydrates or lipids. This depends on the duration of exercise and also the nutritional condition of the sportsman or woman. For strength exercise lasting < 30 min, carbohydrate use is favoured. For endurance exercise lasting > 30 min lipids will be used, enabling naturally-low glycogen reserves to be saved.
20 to 25% of energy enables muscle to be contracted, this is mechanical energy. The remaining 75 to 80% disappears as heat and is lost to the muscles. This low efficiency means it is essential to fill up the reserves.