<P> Muscle weakness may be due to problems with the nerve supply, neuromuscular disease (such as myasthenia gravis) or problems with muscle itself . The latter category includes polymyositis and other muscle disorders . </P> <P> Muscle fatigue may be due to precise molecular changes that occur in vivo with sustained exercise . It has been found that the ryanodine receptor present in skeletal muscle undergoes a conformational change during exercise, resulting in "leaky" channels that are deficient in calcium release . These "leaky" channels may be a contributor to muscle fatigue and decreased exercise capacity . </P> <P> Fatigue has been found to play a big role in limiting performance in just about every individual in every sport . In research studies, participants were found to show reduced voluntary force production in fatigued muscles (measured with concentric, eccentric, and isometric contractions), vertical jump heights, other field tests of lower body power, reduced throwing velocities, reduced kicking power and velocity, less accuracy in throwing and shooting activities, endurance capacity, anaerobic capacity, anaerobic power, mental concentration, and many other performance parameters when sport specific skills are examined . </P> <P> Electromyography is a research technique that allows researchers to look at muscle recruitment in various conditions, by quantifying electrical signals sent to muscle fibers through motor neurons . In general, fatigue protocols have shown increases in EMG data over the course of a fatiguing protocol, but reduced recruitment of muscle fibers in tests of power in fatigued individuals . In most studies, this increase in recruitment during exercise correlated with a decrease in performance (as would be expected in a fatiguing individual). </P>

Muscle fatigue occurs due to the accumulation of