title: Evidence of skeletal muscle damage following electrically stimulated isometric muscle contractions in humans.
abstract: It is unknown whether muscle damage at the level of the sarcomere can be induced without lengthening contractions. To investigate this, we designed a study where seven young, healthy men underwent 30 min of repeated electrical stimulated contraction of m. gastrocnemius medialis, with the ankle and leg locked in a fixed position. Two muscle biopsies were collected 48 h later: one from the stimulated muscle and one from the contralateral leg as a control. The biopsies were analyzed immunohistochemically for inflammatory cell infiltration and intermediate filament disruption. Ultrastructural changes at the level of the z-lines were investigated by transmission electron microscopy. Blood samples were collected for measurement of creatine kinase activity, and muscle soreness was assessed in the days following stimulation. The biopsies from the stimulated muscle revealed macrophage infiltration and desmin-negative staining in a small percentage of myofibers in five and four individuals, respectively. z-Line disruption was evident at varying magnitudes in all subjects and displayed a trend toward a positive correlation (r = 0.73, P = 0.0663) with the force produced by stimulation. Increased muscle soreness in all subjects, combined with a significant increase in creatine kinase activity (P < 0.05), is indirectly suggestive of muscle damage, and the novel findings of the present study, i.e., 1) macrophages infiltration, 2) lack of desmin staining, and 3) z-line disruption, provide direct evidence of damage at the myofiber and sarcomere levels. These data support the hypothesis that muscle damage at the level of the sarcomere can be induced without lengthening muscle contractions.
authors.affiliation: Institute of Sports Medicine Copenhagen, Bispebjerg Hospital, Bldg. 8, Bispebjerg Bakke 23, 2400 Copenhagen NV, Denmark. abigail.mackey@gmail.com
authors.forename: Abigail L
authors.initials: AL
authors.lastname: Mackey
authors.forename: Jens
authors.initials: J
authors.lastname: Bojsen-Moller
authors.forename: Klaus
authors.initials: K
authors.lastname: Qvortrup
authors.forename: Henning
authors.initials: H
authors.lastname: Langberg
authors.forename: Charlotte
authors.initials: C
authors.lastname: Suetta
authors.forename: Kari K
authors.initials: KK
authors.lastname: Kalliokoski
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
authors.forename: S Peter
authors.initials: SP
authors.lastname: Magnusson
mesh_terms: D000328:Adult; D002463:Cell Membrane Permeability; D052283:Creatine Kinase, MM Form / Q000097:blood; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D007537:Isometric Contraction; D008264:Macrophages / Q000648:ultrastructure; D008297:Male; D046529:Microscopy, Electron, Transmission; D018482:Muscle, Skeletal / Q000201:enzymology / Q000648:ultrastructure*; D009135:Muscular Diseases / Q000378:metabolism / Q000473:pathology*; D010146:Pain / Q000378:metabolism / Q000473:pathology*; D010147:Pain Measurement; D012518:Sarcomeres / Q000648:ultrastructure; D013997:Time Factors; D055815:Young Adult
chemical_list: D052283:Creatine Kinase, MM Form