The successful completion of any human physical movement requires the transformation of chemical energy into mechanical energy in skeletal muscles at rates appropriate to their needs. The source of this chemical energy is the hydrolysis of adenosine triphosphate (ATP). However, the amount of ATP stored in skeletal muscle is limited and would only last for a few seconds of contraction. Therefore, the ATP must be regenerated continuously at the same rate as it is broken down if the work rate is to be maintained for a prolonged period of time
