Sarcopenia is defined by the loss of muscle mass and function. In aging sarcopenia is due to mild chronic inflammation but also to fiber-intrinsic defects, such as mitochondrial dysfunction. Age-related sarcopenia is associated with physical disability and lowered quality of life. In addition to skeletal muscle, the nervous tissue is also affected in elderly people. With aging, type 2 fast fibers preferentially undergo denervation and are reinnervated by slow-twitch motor neurons. They spread forming new neuro-muscular junctions with the denervated fibers: the result is an increased proportion of slow fibers that group together since they are associated in the same motor unit. Grouping and fiber type shifting are indeed major histological features of aging skeletal muscle. Exercise has been proposed as an intervention for age-related sarcopenia due to its numerous beneficial effects on muscle mechanical and biochemical features. In 2013, a precursor study in humans was published in the European Journal of Translation Myology (formerly known as Basic and Applied Myology), highlighting the occurrence of reinnervation in the musculature of aged, exercise-trained individuals as compared to the matching control. This paper, entitled «Reinnervation of Vastus lateralis is increased significantly in seniors (70-years old) with a lifelong history of high-level exercise», is now being reprinted for the second issue of the «Ejtm Seminal Paper Series». In this short review we discuss those results in the light of the most recent advances confirming the occurrence of exercise-mediated reinnervation, ultimately preserving muscle structure and function in elderly people who exercise.

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Metallothioneins (Mts) are small molecular weight proteins possessing metal binding and free radical scavenging properties that are upregulated in skeletal muscle following acute spinal cord injury (SCI). We tested the postulate that deficiency of Mt (Mt1 and Mt2; Mt−/−) would exacerbate the development of atrophy, contractile dysfunction, and the oxidative stress response of the soleus following SCI (7 days, T9) compared to control strain mice. Four groups of mice were studied: control transected (CT, n=12); Mt−/− transected (MT; n=12); control laminectomy (CL, n=7); and Mt−/− laminectomy (ML, n=5). CT and MT mice experienced similar % body weight losses following SCI vs. pre‐surgery values. Soleus muscle mass: body mass ratio was lower (p<.05) for CT vs. CL and MT vs. ML groups, with no difference between MT and CT groups. MT mice showed reduced maximal specific tension values at high stimulation frequencies compared to ML animals (p<.05). Furthermore, oxidative stress (4‐hydroxynoneal) and protein levels for the antioxidant catalase were greater (p<.05) in MT vs. ML, but not in CT vs. CL groups. No differences in manganese superoxide dismutase (SOD) or copper‐zinc SOD protein levels were detected between groups. In summary, Mt−/− does not impact muscle mass loss but leads to lower maximal force generating ability and increased oxidative stress of the soleus following acute SCI. Support: Syracuse University SOE

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