Aging protein saps muscle strength.Grandma and grandpa rarely win a weightlifting contest with their grandchildren. As people get old, they begin losing significant amounts of muscle mass, a deterioration scientists call sarcopenia sarcopenia /sar·co·pe·nia/ (sahr?ko-pe´ne-ah) age-related reduction in skeletal muscle mass in the elderly. (SN: 8/10/96, p. 90). Even the muscle that remains in the elderly isn't usually as strong as it once was. At last month's Integrative Biology of Exercise meeting in Portland, Maine, Dawn A. Lowe of the University of Minnesota in Minneapolis and her colleagues offered a clue to why aged muscle is weaker: In older muscle, a key protein, myosin myosin /my·o·sin/ (mi´o-sin) a protein of the myofibril, occurring chiefly in the A band; with actin it forms actomyosin, which is responsible for the contractile properties of muscle. my·o·sin (m, is shirking Shirking The tendency to do less work when the return is smaller. Owners may have more incentive to shirk if they issue equity as opposed to debt, because they retain less ownership interest in the company and therefore may receive a smaller return. Thus, shirking is considered an agency cost of equity. its job. Muscle contraction is, in essence, molecular motion. Armies of myosin proteins simultaneously pull together countless filaments made of the protein actin actin /ac·tin/ (ak´tin) a muscle protein localized in the I band of the myofibrils; acting along with myosin, it is responsible for contraction and relaxation of muscle. It occurs in globular (G-actin) and fibrous (F-actin) forms. ac·tin . The head of the myosin protein mediates this contraction by changing from a state in which it weakly binds actin to one in which it holds firmly. While comparing the muscles of young and elderly male rats, Lowe and her colleagues observed that aged muscle had fewer myosin heads in the strong-binding state during a contraction. Young muscle fibers had about 30 percent of the myosin in that state, while the elderly muscle had only about 22 percent. This may partly explain why aged rat-muscle fibers exert only about 82 percent the force of young muscle. The next step, says Lowe, is to determine why myosin becomes less effective with age. |
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