Every time you throw darts or ride a bike or even work out, you’re engaging your muscle memory. New research from the Norwegian School of Sport Sciences published in Science Advances shows our muscles retain a memory of weakness, as well—and it changes as we age.
Research by Adam P. Sharples published in 2016 showed that there’s an epigenetic component to muscle memory. Sharples and his team studied the genes of participants after two different periods of resistance exercise with a period of rest between. They found that exercise caused muscle cells to upregulate the expression of certain genes—a pattern they remembered during rest, too.
So if muscle use causes upregulation of genes, can muscle disuse cause downregulation? To find out, Sharples and his team reversed his earlier study, looking at the genes expressed in muscle cells of young adults who had repeated leg immobilization. They found a protective pattern of gene expression, with relevant gene pathways being less disrupted during a second period of disuse. In other words, the muscles of young adults proved to be resilient.
Read more: “The Importance of Muscle”
But what about aging muscles? To study the effects of inactivity on gene expression, Sharples and his team compared young and old rats who had similar leg immobilizations. They found that the muscles of old rats developed a detrimental memory of disuse with repeated periods of inactivity causing suppression of relevant genes.
Basically, the research suggests that repeated inactivity causes muscles in the young to develop an expression pattern that helps them recover, while it causes muscles in the old to develop an expression pattern that makes them more susceptible to muscle wasting.
“Muscle carries a history of both strength and weakness, and these molecular memories may accumulate over time to shape how it responds when inactivity occurs again,” Sharples said in a statement. “Understanding how muscle records these past experiences of use and disuse is essential for designing better strategies to support recovery after illness, injury, or age‑related decline.”
Next, Sharples’ team is working with the Novo Nordisk Foundation in Denmark to identify the modes of exercise that produce the most beneficial expression patterns for aging muscles. Until then, we could all stand to get a little more physical activity to give our muscles the best memories—while we still have them. 
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