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Specific Force Deficit in Skeletal Muscles of Old Rats Is Partially Explained by the Existence of Denervated Muscle Fibers

^a Division of Plastic and Reconstructive Surgery, University of Michigan, Ann Arbor
^b Mayo Medical School, Rochester, Minnesota
^c Division of Plastic Surgery, Ohio State University, Columbus
^d Department of Veterans Affairs Medical Center, Ann Arbor, Michigan

Melanie G. Urbanchek, Department of Surgery, University of Michigan, 2130 Taubman Health Care Center, 1500 E. Medical Center Drive, Ann Arbor, MI 48109-0340 E-mail: melurban{at}umich.edu.

Decision Editor: Edward J. Masoro, PhD

We tested the hypothesis that denervated muscle fibers account for part of the specific force (sF_o) deficit observed in muscles from old adult (OA) mammals. Whole muscle force (F_o) was quantified for extensor digitorum longus (EDL) muscles of OA and young adult (YA) rats. EDL muscle sF_o was calculated by dividing F_o by either total muscle fiber cross-sectional area (CSA) or by innervated fiber CSA. Innervated fiber CSA was estimated from EDL muscle cross sections labeled for neural cell adhesion molecules, whose presence is a marker for muscle fiber denervation. EDL muscles from OA rats contained significantly more denervated fibers than muscles from YA rats (5.6% vs 1.1% of total CSA). When compared with YA muscle, OA muscle demonstrated deficits of 34.1% for F_o, 28.3% for sF_o, and 24.9% for sF_o calculated by using innervated CSA as the denominator. Denervated muscle fibers accounted for 11.3% of the specific force difference between normal YA and OA skeletal muscle. Other mechanisms in addition to denervation account for the majority of the sF_o deficit with aging.

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