The effects of strength training and limb immobilization on the human thenar muscles were investigated in 11 healthy subjects. One group (n = 6) trained prior to immobilization and a second group (n = 5) underwent immobilization prior to training. Measurements made in the control condition and following the two experimental conditions included voluntary isometric strength, motor-unit counts, motor nerve conduction velocity, reflex potentiation, and isometric twitch-contraction properties. When the results of both groups were combined an average of 5 wk of immobilization was found to cause a significant decrease in voluntary strength (42%, P less than 0.05) and reflex potentiation (37%, P less than 0.01) in relation to the control condition. Training caused an increase (40%, P less than 0.05) in voluntary strength and a decrease in twitch tension (25%, P less than 0.01) and contraction time (8%, P less than 0.05). Training prior to immobilization provided a reserve of neuromuscular function, which attenuated the effect of immobilization in relation to the control condition. It was concluded that neural as well as muscular adaptation occurred in response to immobilization.