The physical condition of a muscle is determined by its freedom from fatigue, its temperature, its stores of energy foodstuffs, its state of training and its ability to recover from bouts of work. Fatigue reduces the excitability, power and extent of contraction of muscle. Unless the stimulus is great fatigue reduces the number of fibers which respond in repeated muscular contractions. Such reduction in the number of contractile elements reduces the power of the contractions.