Exercise does a lot of good things — it burns calories, helps keep your weight in check and lowers your risk of heart disease, stroke and diabetes. Now add one more thing to the list: physical activity can change your DNA.
Unlike the aberrations and genetic mutations caused by carcinogens and toxins, exercise-induced alterations to DNA are more like tune-ups, helping muscles to work better and more efficiently. What’s more, these changes occur even after a single 20-minute workout.
Juleen Zierath, a professor of physiology at the Karolinska Institute in Stockholm, reports with her colleagues in the journal Cell Metabolism about these very early changes that muscle cells undergo the first time you get off the couch and into the gym. The researchers worked with a group of 14 young men and women who were relatively sedentary, and asked them to work out on an exercise bike that measured their maximum activity levels. The participants also volunteered to give up a little bit of muscle, from their quadriceps, in a relatively painless biopsy procedure performed under local anesthesia. The researchers took the biopsy of muscle cells once before the participants exercised, and again within 20 minutes afterward.
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Using the biopsied samples, researchers compared the activity in a series of muscle-related genes before and after exercise. More genes were turned on in the cells taken after the exercise and the participants’ DNA showed less methylation, a molecular process in which chemicals called methyl groups settle on the DNA and limit the cell’s ability to access, or switch on, certain genes. By controlling how much methylation goes on in certain cells at specific times, the body regulates which genes in the DNA are activated — that’s what differentiates the development of an an eye cell, for example, from that of a liver cell.
Methylation also helps to prime muscle cells for a bout of exercise, getting them to pump out the right enzymes and nutrients the muscle needs to get energy and burn calories while you’re pounding the pavement during that mile-long jog. “We are trying to get at the early messages that the muscle is [receiving in order] to say, ‘Something is happening here, we need to coordinate so we can get more enzymes and more machinery on board so we can cope with the demands of this exercise,’” says Zierath.
The more intense the exercise, she says, the more the methyl groups are on the move. She and her team were able to see this firsthand by comparing gene activity in participants who also agreed to exercise at two different intensities over a period of a week. On one visit, they were asked to cycle until they reached 40% of their maximum capacity; on another occasion, they biked until they reached 80% of their maximum. The muscle biopsies following the 80% sessions showed a lower concentration of methyl groups — and therefore more RNA, which is the first byproduct of gene activity — than samples taken after the 40% sessions.
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To confirm the role of exercise on gene expression in muscle, the scientists then studied how calcium affected the entire system. When muscle cells start to gear up for intense activity like exercise, they release calcium, which fuels the contraction process. When the scientists blocked calcium production, the effect disappeared, and the muscles didn’t contract as much.
That’s when Zierath threw in some coffee — or more specifically, caffeine. Caffeine triggers the release of calcium, and can enhance the way methyl groups move aside to turn on the genes that help muscles contract. When she added caffeine to a lab dish containing cells from the leg muscles of rats, the muscle cells showed lower concentrations of methyl groups and more mRNA — a similar effect as seen after exercise — as she expected.
But, says Zierath, that doesn’t mean you can skip the workout for a cup of coffee instead. “Most of the physiological effect of the caffeine we drink is on the central nervous system, and not dispersed to all the muscles,” she says. “In order to get the same kind of effect we saw in the cells, you would have to drink 50 cups of coffee a day, which is close to the lethal dose. In my mind, half an hour of moderately high intensity exercise is sufficient to do the same thing.”
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Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny . You can also continue the discussion on TIME’s Facebook page and on Twitter at @TIME.