Despite the normally robust regenerative capacity of muscle tissue, extensive soft tissue damage often results in a functional loss that cannot be restored using classic reconstruction techniques. Although implanted biomaterials are capable of mechanically transmitting force generated from the remaining tissue, cellular repopulation, reinnervation and revascularization of the injured area is necessary to achieve complete functional restoration. Using an in vivo tissue engineering model, a 1.0 x 1.0 cm portion of the lateral gastrocnemius (LGAS) of Lewis rats was removed and replaced with a muscle-derived extracellular matrix (ECM). Constructs were seeded with bone marrow-derived (BMSCs) or adipose-derived stem cells (ADSCs) and the peroneal nerve was relocated over the implanted ECM. Creation of the defect resulted in a functional impairment of the LGAS, only capable of producing 85.1 ± 4.1% of the force generated in the contralateral LGAS following ECM implantation. A significant increase in specific tension (SPo) was seen in all groups following the nerve relocation procedure when compared to their corresponding cellular treatment without nerve relocation (p < 0.05). Histological quantification revealed significant increases in cellular content and blood vessel density in the top and bottom regions of ECM implants seeded with BMSCs (p < 0.05). The nerve relocation procedure significantly increased these same variables within the middle region of the ECM when compared to all groups lacking this treatment (p < 0.05). The presence of regenerating myofibers was immunofluorescently confirmed using antibodies against desmin, myosin heavy chain and laminin, while their developmental state was substantiated by the presence of central nuclei. These data corroborate a therapeutic effect of BMSCs on skeletal muscle regeneration within the ECM implant that was not seen following ADSC injection. Furthermore, the nerve relocation procedure stimulated an increased cellular and vascular growth within the middle region of the construct, likely the cause of improved functional output. / text