There are limited data on structural and functional changes in motor endplates and muscle fibers in the target muscle following amputation of the 7th cervical nerve root, a transplantation-related procedure in surgical treatment in the case of avulsions of the brachial plexus roots. We examined functional changes in these structures using stimulated single-fiber electromyography (sSF-EMG) in an animal model. Unilateral amputation of the 7th cervical nerve root was performed in 36 male rats, and the m. triceps brachii muscle was tested by sSF-EMG at different time points. We observed significant differences in the jitter (mean consecutive difference, MCD, of the latencies between adjacent muscle fibers) at post-amputation weeks 1, 2, 4, and 6. The post-operation fiber density (FD) values within the zone of effective stimulation also gradually increased. At post-amputation weeks 8 and 12, the jitter values returned to normal levels, whereas FD values continued to rise. Our results indicate that the post-amputation compensatory processes in the target muscles of the 7th cervical nerve root are mostly completed at 9-12 weeks after amputation.