Advancing age is associated with a reduction in skeletal muscle protein, muscle strength, muscle quality, and chemical modifications that may impair protein function. Sarcopenia has been coupled with physical disability, frailty, and a loss of independent function (5, 19). Using stable isotope tracer methodologies and mass spectrometric detection, we observed: (a) 76–92-year-old physically frail and 62–74-year-old middle-age adults have lower mixed muscle protein synthetic rates than 20–32-year-old men and women; (b) 2 weeks and 3 months of weightlifting exercise increased the synthetic rate of myosin heavy chain (MHC) and mixed muscle proteins to a similar magnitude in frail, middle-age, and young women and men; (c) Serum myostatin-immunoreactive protein levels were elevated in physically frail women and were inversely correlated with lean mass. This suggests that the protein synthetic machinery adapts rapidly to increased contractile activity and that the adaptive response(s) are maintained even in frail elders.
The authors are with the Division of Metabolism, Endocrinology, and Diabetes at the Washington University School of Medicine, St. Louis, MO 63110.