exercise+and+genes - Copy

exercise+and+genes - Copy - Exercise Controls Gene...

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28 American Scientist, Volume 93 © 2005 Sigma Xi, The Scientific Research Society. Reproduction with permission only. Contact [email protected] C onsider what likely would hap- pen in the game show Jeopardy if the category WHAT TISSUES DO were to roll up on the game board. The $200 answer: “It moves the body.” The con- testant delivers the question—”What is Muscle?”—earns her money, and the game quickly moves on. This sce- nario typifies how muscle is generally viewed—as a simple part of the hu- man anatomy that locomotes us. Perhaps late-night television would allow a more sophisticated treatment of muscle’s function. Suppose David Letterman were to ask people on the street “What is skeletal muscle?” Some of the answers might be: “What I see at the meat counter”; “what I feel the day after those rare occasions that I ex- ercise”; and “what I saw on TV during the Olympics.” All these responses in fact vastly underplay the role of muscle, even the subcategory of skeletal muscle, in our bodies. In the following paragraphs, we hope to present a more sophisticated view of the function of skeletal muscle from a genetic and molecular stand- point, and in particular to emphasize the role of skeletal muscle in human health and well-being. Let’s start by recogniz- ing that skeletal muscle is the largest single tissue type in the human body: We have more than 640 muscles, ac- counting for between 30 and 40 percent of total body weight. Skeletal muscle also uses as much as 25 percent of the energy consumed by the body at rest. Furthermore, although today we con- sider Olympic athletes to be extraordi- narily fit, most of our ancestors from tens of thousands of years ago had bodies and muscles that were almost as fit. Many of the metabolic characteristics of modern humans evolved to support high levels of work efficiency and physical activ- ity, a fact that undoubtedly contributes to the health problems facing sedentary 21st-century societies. Our underuse of skeletal muscle may play an underrecog- nized role in the rise of chronic diseases as a cause of modern mortality. Given these few simple facts, it is clear that the importance of skeletal muscle to humans extends well beyond athletics. Plasticity: Genes Get a Workout Skeletal muscle continuously adjusts its composition to meet the acute or chron- ic demands placed on it—a process called plasticity . A very visual example of plasticity is what happens to skel- etal muscle when the daily demand for weight-bearing activity is lost during bed rest, limb immobilization or space flight. One of us (Booth) has shown that one-third of skeletal muscle in an im- mobilized limb can disappear within weeks. It is as if skeletal muscle recog- nizes that it is not needed and “remod- els” itself into weak muscle. The con- verse is also true: If the work demand on muscle increases in a sedentary indi- vidual, even for relatively short periods of time per day (for example, begin- ning an aerobic-exercise program), the
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This note was uploaded on 12/01/2010 for the course BIO SCI Bio Sci E1 taught by Professor Catherineloudin during the Spring '10 term at UC Irvine.

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exercise+and+genes - Copy - Exercise Controls Gene...

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