Induction of relative growth changes in the musculoskeletal system of the sheep by limb immobilisation

The function of the limbs of the sheep was modified to study growth changes in the musculoskeletal system. Seven lambs treated with one hindlimb bound to the body, with the hip fully flexed and the stifle and hock fully extended, were reared from the day after birth to about three months old, together with two untreated controls. The effects of this functional alteration were measured by dissecting and weighing components of the whole carcase, by histometry and electron microscopy of the semitendinosus muscles, and by measurements and ashing of the femurs and tibias. With the particular exception of the hip bone and the muscles extending the hip on the bound side, muscles and bones tended to be heavier on the contralateral side in the hindlimb and on the ipsilateral side in the forelimb. The semitendinosus muscle of the bound limb weighed nearly twice as much as that of the controls. The increase in mass was due to a proportionate enlargement of all the muscle components studied. There was, however, a significant increase in the number of myosine adenosine triphosphatase low reacting fibres, as a percentage of the regional fibre population, in the deeper part of the muscle. It was concluded that the enlargement of the semitendinosus muscle was due to stretch and that the histochemical changes were due to chronic nervous stimulation.