title: Changes in human skeletal muscle ultrastructure and force production after acute resistance exercise.
abstract: Muscle ultrastructure and contractile properties were examined before and after a single bout of resistance exercise (8 sets of 8 repetitions at 80% of 1 repetition maximum). Eight untrained males performed the concentric (Con) phase of arm-curl exercise with one arm and the eccentric (Ecc) phase with the other arm. Needle biopsies were obtained from biceps brachii before exercise (Base), immediately postexercise from each arm (post-Con and post-Ecc), and 48 h postexercise from each arm (48 h-Con and 48 h-Ecc). Electron microscopy was used to quantify the presence of disrupted fibers in each sample. Analysis of variance revealed a greater (P < or = 0.05) proportion of disrupted fibers in post-Con, post-Ecc, 48 h-Con, and 48 h-Ecc samples compared with Base. Significantly more fibers were disrupted in post-Ecc (82%) and 48 h-Ecc (80%) samples compared with post-Con (33%) and 48 h-Con (37%), respectively. Voluntary and evoked strength measurements recovered to Base values within 24 h in the Con arm but remained depressed (P < or = 0.05) for 72-96 h in the Ecc arm. These data indicate that both the raising and lowering phases of weightlifting produced myofibrillar disruption, with the greatest disruption occurring during the lowering phase.
authors.affiliation: Department of Kinesiology, McMaster University, Hamilton, Ontario, Canada.
authors.forename: M J
authors.initials: MJ
authors.lastname: Gibala
authors.forename: J D
authors.initials: JD
authors.lastname: MacDougall
authors.forename: M A
authors.initials: MA
authors.lastname: Tarnopolsky
authors.forename: W T
authors.initials: WT
authors.lastname: Stauber
authors.forename: A
authors.initials: A
authors.lastname: Elorriaga
mesh_terms: D000328:Adult; D004576:Electromyography; D006801:Humans; D007537:Isometric Contraction / Q000502:physiology; D008297:Male; D008854:Microscopy, Electron; D018485:Muscle Fibers, Skeletal / Q000502:physiology / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000502:physiology* / Q000648:ultrastructure*; D009210:Myofibrils / Q000502:physiology / Q000648:ultrastructure; D013997:Time Factors; D014891:Weight Lifting / Q000502:physiology*