Effects of Intramuscular Mesenchymal Stem Cell and Boric Acid Administration on Muscle Damage and Recovery in an Exhaustive Swimming Rat Model.

Exhaustive exercise induces damage to skeletal muscle, reducing athletic performance and delaying recovery. Effective experimental strategies are needed to mitigate this damage and accelerate tissue regeneration. This study aimed to address limitations in the therapeutic efficacy of bone marrow-derived mesenchymal stromal/stem cell-like cells (MSCs) associated with limited cell viability by evaluating boric acid (BA) as an antioxidant and metabolic modulator to enhance cell viability and muscle repair. Twenty-five female Wistar albino rats underwent a 15 day exhaustive swimming protocol and received intramuscular injections of MSCs (1 × 106 cells), BA (10 µg), or their combination, according to the experimental group allocation. Bone marrow obtained from five additional donor rats was used exclusively for MSC isolation and culture. Daily exhaustion time, serum biomarkers lactate, lactate dehydrogenase (LDH), creatine kinase (CK), and gastrocnemius histology were evaluated. Intramuscular BA improved endurance and reduced biochemical markers of muscle injury, whereas MSC application promoted structural muscle regeneration, as evidenced by centrally located nuclei and improved muscle fiber integrity. Combined MSCs + BA treatment improved several biochemical and histological outcomes compared with exercise alone. Serum lactate concentrations remained elevated in treated groups 24 h after the final exercise session, indicating altered post-exercise metabolic responses. Overall, intramuscular BA modulated metabolic responses, whereas administration of bone marrow-derived stromal/stem cell-like cells was associated with structural regeneration in this rat model of exercise-induced skeletal muscle injury, providing a reproducible platform for evaluating regenerative interventions.