Muscular dystrophy comprises a heterogeneous group of inherited neuromuscular disorders characterized by progressive muscle degeneration, weakness, and functional decline. In the absence of curative pharmacologic therapies, non-pharmacologic strategies aimed at preserving muscle mass and function are of growing clinical importance. Exercise therapy is an established cornerstone of conservative management, whereas cannabidiol supplementation has emerged as a novel experimental intervention supported primarily by preclinical evidence. This systematic review synthesizes and compares the available evidence on exercise therapy and cannabidiol supplementation with respect to muscle mass preservation in muscular dystrophy. Exercise interventions, including aerobic, resistance, and functional training, demonstrate modest but consistent benefits in functional performance, endurance, and quality of life, with acceptable safety profiles when appropriately individualized. In contrast, cannabidiol supplementation has shown promising anti-inflammatory, anti-fibrotic, and myoprotective effects in dystrophic animal models, yet lacks robust human clinical data. Comparative analysis suggests overlapping anti-inflammatory and antioxidant mechanisms, raising the possibility of synergistic benefit; however, combined intervention strategies remain untested. Overall, exercise therapy remains the most evidence-supported approach for muscle preservation in muscular dystrophy, while cannabidiol supplementation warrants cautious investigation through rigorously designed clinical trials. Future research should prioritize head-to-head randomized controlled trials, standardized outcome measures, and subtype-specific therapeutic strategies to clarify the independent and complementary roles of these interventions.