STUDIES ON FIBER TYPE TRANSFORMATION OF THE PROCESS OF SKELETAL MUSCLE INJURY AND REGENERATION AFTER ECCENTRIC EXERCISE.

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Muscle damage and/or injury generally occurs in response to the eccentric component of intense muscular activity. This study assumed that muscle fiber transformation is indicated by injury and experiment on determination whether this hypothesis is good or not.Skeletal muscle injury after downhill running was estimated from histochemical analysis of muscle cross-sections by determing the numbers of intact fibers per unit area in the muscle of rats. Two or three days after downhill running the tetanic tension by indirected stimulation was less than direct stimulate tension, and some endplates showed unfusimotor axons. Collateral and terminal sprouting were also seen in plantaris muscle after downhill running. Many of the reinnervated endplates were supplied by nerve branches from two or more different axons, and only gradullaly did this polyneuronal innervation subsided. A significant conversion of type IIb into type IIa fiber with nine weeks endurance training involved downhill running was observed.It is concluded that increases in muscle fiber transformation occur after downhill running induced injury and regeneration may have a role in the etiology of the neuromuscular junction injury process.