抄録
Muscle hyperplasia, an increase in the number of muscle fibers, occurs as a result of two mechanisms related to satellite cells. One mechanism is a splitting or branching of muscle fibers, and the other is a new formation of muscle fibers. Skeletal muscle hypertrophy generally occurs due to hypertrophy of muscle fibers themselves, but it remains controversial as to whether or not it is actually associated with hyperplasia. To prove hyperplasia, measurement of the number of muscle fibers is necessary. Two methods are available for making such a measurement: a direct method which counts all muscle fibers in a sample of muscle, and an indirect method which estimates all muscle fibers from several biopsy specimens and the relative cross sectional area of the muscle biopsy site. Both methods have their own limitations. In general, the number of muscle fibers is measured with a direct method in animals and with an indirect method in humans. Several reports have shown an increase in the number muscle fibers in animals under isotonic, high load and short duration exercises. Muscle regeneration after muscle injuries incurred during exercises are considered as a factor in hyperplasia induced by exercise. Such regeneration has mainly been evaluated as satellite cell activity, and several reports have demonstrated that this type of regeneration can be promoted by growth factors, ultrasound, and muscle stretching. There remains a need to investigate the effect of various promoters and exercises on hyperplasia, and we expect to clinically apply the results obtained with these basic studies.
