Exercise Initiation After Surgical Reconstruction for Rat Rotator Cuff Injury Affects Tendon Healing and Muscle Preservation

This study investigates how postoperative exercise timing influences tendon healing and muscle preservation following supraspinatus tendon reconstruction in a rat rotator cuff injury model. Five experimental groups—Sham, cage activity, immobilization (IM), immobilization with early exercise (IM+EE), and immobilization with delayed exercise (IM+DE)—were evaluated at 3 and 6 weeks post-surgery through histological scoring, collagen organization analysis, muscle fiber morphology, and biomechanical load-to-failure testing. Early exercise during the inflammatory phase (IM+EE) worsened histological degenerative markers and increased vascularity, while delayed exercise (IM+DE) produced more favorable collagen stainability and remodeling characteristics at 6 weeks. Immobilization alone supported early collagen maturation and mitigated inflammatory overactivation compared to cage activity. Muscle histology showed that immobilization-associated atrophy occurred during the first 3 weeks but improved with subsequent activity. Overall, findings demonstrate that excessive early mechanical loading delays tendon healing, while moderate exercise introduced after early inflammation subsides may support more effective long-term recovery.