Stretch-Induced Healing of Injured Muscles Is Associated With Myogenesis and Decreased Fibrosis

Background: Alghouth therapeutic stretching exercise has been applied to accelerate the healing of injured skeletal muscles, mechanisms behind the mechanical stretch-induced muscle recovery remain unclear. Purpose: To examine stretch-associated antifibrotic and myogenic responses in injured muscles and to evaluate the feasibility of the ultrasonic Nakagami parametric index (NPI) in assessing muscle morphology during recovery. Study Design: Controlled laboratory study. Methods: Skeletal muscle fibrosis was induced in the right hind legs of 48 rats by making a posterior transverse incision in the gastrocnemius muscle; the left hind legs remained intact as a comparative normal reference. After surgery, the 48 rats were randomly divided into the stretch (S) and control (C) groups. The S group received stretching interventions on the injured hind leg from week 3 to week 7 after surgery, while the C group did not receive stretching throughout the study period. The muscle fibrosis percentage and the ultrasonic NPI were examined sequentially after surgery. Relative expressions of myogenesis-related proteins, including myoblast determination protein 1 (MyoD), myogenin, and embryonic myosin heavy chain (MHCemb), were also evaluated during the follow-up. Results: Mean fibrosis percentages in the injured hind leg were approximately 25% at week 3 in both groups, but they were significantly decreased by approximately 20% from week 4 to the end of the follow-up in the S group only (all, P <.05). Upon injury, the NPI values of injured hind legs in both groups dramatically dropped. Within the S group, stretching increased the NPI values of injured hind legs, which approached those of control hind legs at weeks 6 and 7. The highest MyoD, myogenin, and MHCemb levels were observed at week 6 in both groups. The NPI values corresponded to the MyoD expression in the S group during the follow-up. Conclusion: Stretching induced a decrease in muscle fibrosis and an increase in myogenesis in injured muscles. The NPI values correspond to the myogenesis process. Clinical Relevance: The NPI may be capable of continuously monitoring the injured skeletal muscle morphology during the healing process in clinical settings.