Recovery of function in skeletal muscle following 2 different contraction-induced injuries

Objective: To determine if the proliferation of myogenic cells is equally important to recovery of contractile function after 2 different types of contraction-induced muscle injuries. Design: Randomized trial. Setting: Muscle biology laboratory. Animals: Adult male Sprague-Dawley rats. Interventions: Tibialis anterior muscles were injured by a single lengthening contraction with large strain (IR) or multiple lengthening contractions with small strain (MR). The hindlimbs of some animals in each group were irradiated before injury to prevent proliferation of myogenic cells during recovery. Main Outcome Measures: Contractile tension was measured immediately after injury and 3, 7, 14, and 21 days after injury. Permeation to Evans blue dye was used to assay membrane damage. Centrally nucleated fibers and reverse transcriptase-polymerase chain reaction of myoD and myogenin were used as measures of myogenesis. Results: Inhibiting myogenesis prevented the recovery of contractile function after MR, but not after IR. Both protocols caused Evans blue dye uptake immediately after injury, but Evans blue dye was only retained in fibers for several days after IR. This suggests that membranes reseal after IR, but not after MR. Conclusions: The mechanisms that underlie recovery after injuries caused by repeated lengthening contractions and injuries caused by a single lengthening contraction are different. The differences may be important when planning targeted rehabilitation strategies for each type of injury.