This study examines muscle recovery and related changes in the motor unit population of 'hyper-reinnervated' rat skeletal muscle. Medial gastrocnemius (MG) muscles were hyper-reinnervated by either cutting the MG nerve and implanting it on the MG muscle together with additional hind limb nerves, or by crushing the MG nerve and excising the medial portion (50-70%) of the MG muscle. Our findings were that muscles hyper-reinnervated with multiple nerves recovered muscle mass and strength more fully than did the self-reinnervated muscles, more motor units were formed (up to three times the normal number were found), and the mean motor unit size was significantly smaller. A relatively small percentage of muscle fibers became polyneuronally innervated. In contrast, the number of motor units that were formed in the muscle reduction experiments were not significantly larger than was expected considering the mass of the muscles. We conclude that hyper-reinnervation improves muscle recovery, it may be a useful technique for improving function in denervated muscle, and may serve to provide added sources of EMG control signals in some amputees.