After two years of Covid-19 and its disruption in our exercise routines, many of us may feel like we have forgotten how to be in good shape. But an encouraging new study suggests our muscles remember. The study looked at mice, but it draws on similar experiences with bodybuilding and people. He found that muscles developed a ubiquitous and lasting molecular “memory” from past resistance exercises that helped them bounce back quickly after long layoffs.

In the study, animals that took some form of resistance training in rodents developed changes in their muscle DNA that persisted long after they stopped exercising. The mice then built up muscle mass much faster than other animals when they resumed training. And as an encouraging side note for those new to weight training, the results also suggest that we should be able to build new muscle memories regardless of our age.

Until recently, the term “muscle memory” generally described our ability to cycle, ski, throw to first base, or repeat other common physical tasks, even if we had not pedaled, schussed, or steered. baseball for years. Our bodies remember how. But this type of memory, while real, is not really muscle memory. These memories exist in the motor neurons of our brain.

But scientists knew that something happened in the muscles themselves when they worked hard, especially during weight training, and that these changes affected the way the muscles later responded to exercise. “For the record, people say things like, ‘I was an athlete and then I took time off but my muscles came back as soon as I started’ ‘lifting weights again, said Kevin Murach, professor of health and human performance at the University of Arkansas, who oversaw the new study.

These stories piqued his interest and that of other researchers. How, they wondered, do muscles “remember” past workouts? And in what ways do these memories help muscles rebound after being out of the gym?

Some preliminary studies with animals have suggested that the genes inside the nuclei of muscle cells work differently after resistance exercise. Then, in 2018 and 2019, several much-discussed studies of people looked at the epigenetics of resistance training. Epigenetics refers to changes in how genes work, even if the gene itself does not change. This primarily involves a process called methylation, in which groups of atoms, called methyl groups, attach themselves to the outside of genes like tiny barnacles, making the genes more or less likely to turn on and produce specific proteins.

In recent human experiments, resistance exercise altered the methylation patterns of a number of genes in people’s muscles, and these changes remained evident weeks or months later, even after the volunteers quit. to exercise and lost some of their muscle mass. When they started lifting again, they gained muscle much faster than they started in the studies, the researchers found. Basically their muscles remembered how to grow taller.

But these studies, while intriguing, lasted a few months at most. It was not yet clear whether the exercise from much longer ago would persist as genetic memory in our muscles, or how many different cells and genes in muscles would be epigenetically affected by resistance training.

So for the new study, recently published in Function, a flagship journal of the American Physiological Society, Dr Murach and his colleagues, including lead author Yuan Wen of the University of Kentucky, decided to recreate the experiments of human bodybuilding. as close as possible in adult mice. The lifespan of rodents is much more condensed than ours, which means that the changes seen in animals after several months can appear in humans after several years.

But since mice can’t use dumbbells, scientists had them run on weighted running wheels, designed to provide resistance training to the muscles of the legs. The animals trained for eight weeks, then sat in their cages for 12 weeks, about 10 percent of their lifespan, which would be years for us. The animals then trained again for a month, joined by mice of the same age who were new to the exercise and served as controls. All along, the researchers biopsied and studied their muscles under a microscope.

They noted many differences in gene methylation in muscle cells after training mice; most of the changes remained for months after stopping exercise. In general, these epigenetic changes turned on the functioning of genes involved in muscle growth while calming the activity of genes elsewhere, making the genetic process of muscle building “more refined,” said Dr Murach. Even after months of inactivity, these changes helped trained mice add more muscle faster during retraining, compared to mice that had not been trained before.

Of course, this study involved mice, not people. He also looked only at resistance exercise and not aerobic workouts.

But since many of the genes the researchers are tracking are the same ones the researchers studied in human experiments, the results are most likely relevant to all of us hoping to build muscle in 2022. They suggest that:

  • It may never be too late to start building muscle memories, even if we have rarely or never lifted weights. The mice in the study were all adults when they started the weight-wheel workouts, but they were all successful in creating muscle memories that allowed them to build muscle faster after a period of inactivity. “It’s better to start at some point than not at all,” said Dr Murach.