Histological changes of the skeletal muscle due to muscle tension: a study in rats.

OBJECTIVE To analyze the influence of muscle tension in the histological changes of the skeletal muscle. METHODS Fifty-four Sprague-Dawley (SD) rats were randomly divided into 3 groups. The left gastrocnemius muscles of the rats were dissected with only the neurovascular pedicles intact; the tibial nerves were cut and immediately repaired by epineurial suture. Then the Achilles tendons were isolated and treated accordingly; the Achilles tendon were lengthened by 0.5 cm in lengthened group, shortened by 0.5 cm in shortened group and left alone in normal (control) group. In the 2nd, 4th and 8th weeks after operation, the specimens were taken from gastrocnemius muscle for histological study by light and electron microscope. RESULTS In comparison between the groups, the gastrocnemius muscles in the shortened group showed less severe muscle atrophy and connective tissue proliferation, bigger diameter and cross section area of the muscle fibre than those in the normal and lengthened groups in all the postoperative periods. CONCLUSION A proper high tension of the muscle may decrease the muscle dystrophy and stops the histological changes of skeletal muscle by having much longer fibre length and bigger cross sectional area. Also increases the muscle function as the muscle active force-generating range is determined by muscle fibre length, while maximum muscle force is determined by physiologic cross-sectional area.