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Passive Stretches Protect Skeletal Muscle of Adult and Old Mice From Lengthening Contraction-Induced Injury

¹ School of Kinesiology, University of Illinois at Chicago.
² Department of Kinesiology, University of Toledo, Ohio.
³ Institute of Gerontology, University of Michigan, Ann Arbor.

We tested the hypothesis that a single bout of training with passive stretches or isometric contractions protects the extensor digitorum longus muscle in old mice from contraction-induced injury. Lengthening contractions produced similar decreases in force (70%–80%) and numbers of overtly injured fibers (15%–20%) in adult and old mice, but twofold greater inflammatory cell accumulation above untreated control values in old versus adult mice. For both age groups, prior training with passive stretches improved postinjury force almost twofold compared with untrained muscles and reduced injured fibers by one half. Training with passive stretches or isometric contractions reduced inflammatory cell accumulation following lengthening contractions by as much as two thirds in old mice, but not in adult mice. The data indicate that passive stretches provide some protection against contraction-induced injury in old mice, and that accumulation of inflammatory cells does not correlate strongly with force deficit and number of injured fibers.