NORMAL FORCES AND MYOFIBRILLAR DISRUPTION AFTER REPEATED ECCENTRIC EXERCISE

To investigate the ''rapid-adaptation'' phenomenon, we examined force, neural, and morphological adaptations in 12 subjects who performed 10 0 eccentric contractions with the quadriceps muscle (bout I) and repea ted the same exercise after a 2-wk. hiatus (bout 2). Two days after bo ut I, quadriceps muscle strength and surface electromyographic (EMG) a ctivity declined similar to 37 and 28%. respectively, in the control g roup (n = 6). At day 2 after bout I, significant increases occurred in patellar tendon reflex amplitude (similar to 25%), muscle soreness (f ivefold), and serum creatine kinase (220%), and 65 +/- 12% of the tota l number of pixels in the EMG indicated myofibrillar disruption. At-da y 7 after bout 1, all variables returned to normal. At day 2 after bou t 2, no significant changes occurred in force, EMG, creatine-kinase, o r soreness, but reflex amplitude increased, and 23 +/- 4% of the total number of pixels in the EMG still indicated myofibrillar disruption. The results suggest that the rapid force recovery following eccentric exercise is mediated at least in part by neural factors and that this recovery may occur independently of cell disruption.