Healing of a crush injury in rat striated muscle. 4. Effect of early mobilization and immobilization on the tensile properties of gastrocnemius muscle.

Tensile properties of partially crushed gastrocnemius muscle were studied and compared with the uninjured control muscles of 185 rats after treatment by mobilization on the treadmill or immobilization in a softened plaster cast. Two to 42 days after a reproducible injury induced to the left calf of the rat, load-deformation curves were registered from both gastrocnemius muslce and several parameters were assessed from the curves. The rupture site was studied macroscopically as well as histologically. In injured muscles the rupture was usually observed at or near to the injury (92%) when in intact muscles the rupture most often (94%) occurred at the muscle belly. The decrease in breaking strength and energy absorption due to the injury was rather constant (20-25%) on day 2 after trauma. Thereafter in mobilized muscles these values, as well as those of elastic stiffness, returned to the level of the uninjured control muscles more rapidly than in immobilized muscles, where a decrease in tensile properties at the end of the first week was on an average 20-30% and fell still further to 30-40% towards the end of the immobilization period (21 days). Three weeks after the removal of the casts these values in the previously immobilized muscles had not yet reached the level of the controlateral control muscles.