Exercise Controls Gene Expression
The activity level of skeletal muscle modulates a range of genes that produce dramatic molecular changes—and keep us healthy
Consider what likely would happen 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 contestant
delivers the question—"What is Muscle?"—earns
her money, and the game quickly moves on. This scenario typifies how
muscle is generally viewed—as a simple part of the human
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
exercise"; 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
standpoint, and in particular to emphasize the role of skeletal
muscle in human health and well-being. Let's start by recognizing
that skeletal muscle is the largest single tissue type in the human
body: We have more than 640 muscles, accounting 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 consider Olympic athletes to be
extraordinarily 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 activity, a fact that
undoubtedly contributes to the health problems facing sedentary
21st-century societies. Our underuse of skeletal muscle may play an
underrecognized 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.