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J Gerontol A Biol Sci Med Sci. 2009 Jun;64(6):618-28. doi: 10.1093/gerona/glp026. Epub 2009 Apr 7.

Age-related deficit in load-induced skeletal muscle growth.

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  • 1Department of Neurobiology, Physiology, and Behavior, University of California, Davis, 95616, USA.


The growth response of ankle flexor and extensor muscles to two models of increased loading, functional overload (FO) and hind-limb reloading following hind-limb suspension, was measured by wet weight in Fisher 344-Brown Norway rats at ages ranging from 6 to 30 months. In response to FO, there was a 40% decrease in absolute growth of the plantaris beginning in middle age. Interestingly, the growth response to FO of 30-month old rats maintained on a 40% calorie-restricted diet improved by more than twofold relative to 30-month old rats on a normal chow diet. Recovery of muscle mass upon reloading following disuse was significantly impaired (reduced 7-16%) in predominantly fast, but not slow, muscles of 30-month relative to 9-month old rats. Initial investigation of the Akt signaling pathway following FO suggests a reduction or delay in activation of Akt and its downstream targets in response to increased loading in old rats.

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