Introduction: The beneficial effects of the overexpression of Jagged-1 were described in escaper golden retriever muscular dystrophy (GRMD) dogs that had a near-normal life. Additionally, overexpression of Jag1 improved the phenotype in dystrophin-deficient zebrafish. Here, we show updated findings on a dystrophin-deficient mouse model overexpressing human JAG1 (mdx5cv-JAG1) compared with controls mdx5cv. Methods: Animals were studied at three time points: one, four, and twelve months. TA muscles were used for in situ physiology. Quadriceps muscles were used for proteomics. Results: (1) Muscle-specific overexpression of JAG1 leads to increased muscle mass starting from four months, resulting in higher ratios of muscle weight/body weight. (2) In situ physiology showed increased force in mdx5cv-JAG1 muscles from four- and twelve-month-old animals. (3) Proteomics data using muscles collected at the three time points show changes in metabolic and muscle-related pathways, and its interaction with essential proteins related to muscle repair and growth. Conclusion: Our data supports the beneficial role of JAG1 overexpression in dystrophin-deficient muscles and suggests an interaction of jagged-1 with muscle repair mechanisms.