Normal forces and myofibrillar disruption after repeated eccentric exercise

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Abstract
Hortobágyi, Tibor, Joseph Houmard, David Fraser, Ronald Dudek, Jean Lambert, and James Tracy. Normal forces and myofibrillar disruption after repeated eccentric exercise.J. Appl. Physiol. 84(2): 492–498, 1998.—To investigate the “rapid-adaptation” phenomenon, we examined force, neural, and morphological adaptations in 12 subjects who performed 100 eccentric contractions with the quadriceps muscle (bout 1) and repeated the same exercise after a 2-wk hiatus (bout 2). Two days after bout 1, quadriceps muscle strength and surface electromyographic (EMG) activity declined ∼37 and 28%, respectively, in the control group (n = 6). Atday 2 after bout 1, significant increases occurred in patellar tendon reflex amplitude (∼25%), muscle soreness (fivefold), and serum creatine kinase (220%), and 65 ± 12% of the total number of pixels in the EMG indicated myofibrillar disruption. At day 7 after bout 1, all variables returned to normal. At day 2after bout 2, no significant changes occurred in force, EMG, creatine kinase, or 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.