Therapeutic effect of passive mobilization exercise on improvement of muscle regeneration and prevention of fibrosis after laceration injury of rat

Objective: To evaluate the muscle healing effect of passive mobilization exercises after a laceration injury. Design: Randomized controlled trial. Setting: Basic science laboratory. Animals: Male Sprague-Dawley rats (N=36), age ranging from 8 to 10 weeks and weight ranging from 300 to 400g. Intervention: The bilateral gastrocnemius muscles were lacerated. The left leg muscles were used as the study groups and the right side was used as the control (lacerated muscles without any treatment, n=8). In the exercise group (n=24), passive mobilization exercise (15min/d) was performed for 5 days starting from different time points (2, 7, and 14d postlaceration). The decorin group (n=8) was injected with decorin (50μg at 14d postlaceration), which is a well-known antifibrotic agent. Four animals were used as the normal controls, in which only the muscle strength was evaluated. All the animals were killed 4 weeks after the laceration. Main Outcome Measures: The histologic characterization of muscle regeneration (hematoxylin and eosin staining, number and diameter of the centronucleated, regenerating myofibers), muscle fibrosis (vimentin-positive area, Masson modified trichrome staining positive area), and muscle strength (analysis of fast twitch strength). Results: The level of fibrosis was more than 50% lower in the exercise and decorin groups than in the control (P<.05). The decorin group showed the highest number of regenerated, new myofibers and the highest muscle strength. All of the exercise groups, regardless of the starting time of exercise, also showed significant improvement in regeneration and strength. However, the exercise group starting 14 days after the laceration showed the best results. Conclusions: Stretching exercises after a muscle laceration injury has a strong antifibrotic effect, as much as a well-known antifibrotic agent, decorin. According to the results, the best time to begin stretching exercises is 14 days after laceration for antifibrosis and muscle regeneration.