It’s not a fitness myth: There really is such a thing as muscle memory, although it may not mean exactly what you think it does.
Although people colloquially refer to never forgetting how to ride a bike, throw a baseball or serve a tennis ball as examples of “muscle memory,” those comeback skills actually stem from a motor learning process. In other words, they are “motor memory.” When you learn how to perform these movements well and can do them automatically without conscious thought, that information becomes encoded in the brain, so in the future, “you still have the fundamental coordination that you learned,” explained David Behm, a university research professor in the School of Human Kinetics and Recreation at the Memorial University of Newfoundland in Canada.
When exercise physiologists talk about muscle memory, on the other hand, they’re referring to the phenomenon whereby previously trained muscles acquire strength and volume after a period of disuse much more quickly than never-trained muscles do when starting from scratch.
In the past 15 years, research has shown that the changes actually persist in the muscles themselves. In one study of mice, for example, the results suggest that after nuclei in muscle cells proliferate in response to an overload of training, those extra nuclei aren’t lost during subsequent periods of inactivity. They’re retained in distinct muscle fibers, essentially waiting to be reactivated with retraining.
When you exercise, it’s normal for muscle fibers to experience minor damage; this is part of the way a muscle gets stronger. Dormant cells called satellite cells move to the site of the injury and insert more nuclei — the brains of the cells — into the muscle fibers, which allows the muscle to grow, explained exercise physiologist Fabio Comana, a lecturer in exercise and nutritional sciences at San Diego State University. Even if you stop exercising for a significant period of time, he said, “the nuclei stay [in place] and accelerate the return to muscle growth” with retraining.
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Another area of research into muscle memory relates to changes to the ways your genes work in response to your environment and behavior, according to Kevin Murach, an assistant professor of health, human performance and recreation at the University of Arkansas at Fayetteville. “In the muscle cells, genes get turned on and off in response to exercise in order to make certain proteins in the cell, which ultimately facilitates muscle growth and strength,” he said. According to this theory, long-term changes to these genes could be what drives muscle memory.
One way or another, this much is clear: The more you exercise, the more (muscle memory) savings you’ll accrue. “Once you’ve got those additional nuclei, they’re in reserve. You’re banking that capacity,” said Lawrence Schwartz, a professor of biology at the University of Massachusetts Amherst. “You essentially have an instrumental manual for making muscle, so you can get enhanced growth much faster the second time around.”
And researchers believe muscle memory is long lasting, maybe even permanent. “There’s never an age where it stops,” Behm said. In fact, a recent study involving men in their 50s to 70s investigated the effects of completing a resistance training regimen, followed by a detraining period, then a retraining period, each consisting of 12 weeks. As expected, resistance training increased knee extension strength and power by 10 to 36 percent. Detraining resulted in a 5 to 15 percent loss of strength and power. The big reveal: “Less than eight weeks of retraining were needed to reach the post-training level of … maximum strength,” according to the researchers.
But how quickly you regain your former fitness depends on how fit you were initially, how long the layoff was, how old you are and how long you’d been exercising to establish your muscle memory, according to Cedric Bryant, president and chief science officer of the American Council on Exercise. “The more fit you are and the longer you established that muscle memory,” he said, “the more the odds tilt in your favor.”
All this news about muscle memory should be encouraging for those who fell off the fitness wagon during the pandemic. It means you’re not starting from square one; you have a distinct advantage when it comes to regaining your former level of fitness. And the principles apply to both resistance training and endurance training, according to Cory Dungan, an assistant professor in exercise physiology at Baylor University.
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With strength training, Comana recommends using this principle for weight progression to avoid injuring yourself when you resume weight training: If you’re doing three sets of 10 reps for two or three weeks, once you get to the point where you feel as if you could do two more reps until you reach the point of failure, then it’s time to add a little more weight.
With aerobic exercise, the best way to rekindle your muscle memory is to ease into your workouts again. “Start at a level below what you were accustomed to doing, then gradually increase in terms of duration, frequency, then intensity,” Bryant said. “Do the minimum effective dose. Moderately challenging should be enough to set you on a course of regaining fitness. Don’t try to go from zero to 60 in terms of ramping up too soon.”
Instead, it’s generally safe to increase these elements by 5 percent every week or two as you feel comfortable, Bryant said. This means that if your goal is to do 150 minutes of aerobic exercise per week, which amounts to five 30-minute sessions, you could start with 15-to-20-minute sessions at an intensity where you can speak but not sing, he said. “Then add five minutes per week until you get to where you were.” Then you can increase the intensity of your workouts, perhaps by adding higher-intensity intervals to your baseline pace.
To hone your skills with a particular sport, such as tennis, soccer or golf, focus more on how you can take advantage of the motor-neuron process. “You can use mental imagery to send messages to those neurons that will turn on when you want to do that movement,” Behm said. It may also help to watch videos where other people are playing that sport, because this will activate the mirror neurons in your brain, he added. (When you watch sports, specific neurons in your brain will fire as if you were playing the sport yourself.)
Ultimately, it helps to think of muscle memory as a payoff for all the past work you put into learning a sport, boosting your aerobic capacity or endurance, or building muscle and strength. The best way to tap into muscle memory is to “get back on the horse,” Murach said. “You will never know how much muscle memory you may have until you start training again.”