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Muscle mass is hard to lose—so don’t sweat it, okay?

Kells McPhillips

Kells McPhillipsApril 20, 2020

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Photo: Stocksy / Jeff Way

None of our workout routines look the way they did a few months ago, and that’s okay. As we’re reorganizing our lives and defining “at-home” gym for ourselves, you may find yourself wondering: “How long does it take to lose muscle mass?” I asked Roger Luo, MD, assistant professor of spine and musculoskeletal medicine at the Rutgers New Jersey Medical School, to break down the science behind building and losing your pump.

“To ‘lose muscle mass’ generally refers to muscular atrophy, or the decrease in size and/or number of muscle fibers that occurs when a person has decreased activity or training,” says Dr. Luo. “This can be in the case of immobility—due to injury or in the hospital setting—or compared to a person’s baseline. For example, if you take an athlete who is accustomed to lifting a certain amount of weight, or training with a certain frequency and suddenly halts their training, you can expect some ‘loss’ to occur with time if the activity is much reduced compared to baseline.”

For most people, these fluctuations in muscle size naturally occur as life ebbs and flows, but research isn’t yet rock-solid on how long the process takes. “We are failing to account for so many variables: sex, age, training history, genetics, nutrition, and much more,” says Dr. Luo. What researchers do know? “At the extreme, if a person is fully immobilized and lying down—meaning, they’re not even supporting their own body weight—previous data suggest that muscle atrophy is slow for the first two days, but speeds up.” After two weeks of full immobility, research indicates that a person will lose about half their muscle mass and continue to lose more should their immobility continue.

Again, though, this is the most extreme case of inactivity. While you’re quarantining, you’re likely at least pacing around the house, taking walks outside, or yoga-ing in your living room. And while doctors like Luo cannot yet quantify exactly how effectively those activities are maintaining your muscle mass, he says you’re not going to lose years of gains overnight. “For a well-trained person, it would probably take significantly more inactivity than the average person to negate years of work,” he says. “Aerobic conditioning [like running, swimming, biking, or dancing] tends to be more easily lost, and more easily recovered. It takes longer to build and longer to lose muscle mass compared to cardiovascular conditioning.”

Now, perhaps more than ever before, it’s important to be compassionate with your body. “It’s important to keep in mind during these trying times that any activity is better than no activity, and you do not need very much space at all to get a great workout in. Running in place, jumping jacks, jumping rope, jogging up and down the stairs in addition to calisthenics does not require very much equipment at all,” says Dr. Luo. Your biceps aren’t going to evaporate overnight, and your belief that you’re strong AF shouldn’t either.

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