No such thing as ‘use it or lose it’, researchers find.

Image in public domain.

Quite often, our muscles do things without us truly thinking about it. Whether it’s playing the guitar, riding a bike, or simply typing your password at the ATM, we’re all familiar with our muscles doing things “without us”. These and other forms muscle memory have been a puzzling matter of debate for decades, and researchers are still discovering more and more things about how this actually works.

But if you don’t use them regularly, do you use that ability? In other words, is it “use it or lose it”?

Muscle memory

Muscle memory is a term used to describe  tasks which seems to be easier to perform after previous practice — even if the practice happened a very long time ago. It’s as if the muscles “remember” what happens and are quicker to return to their previous capacity.

This doesn’t only affect things you do, but also the muscle mass and training, which helps to explain why strength-trained athletes experience a rapid return of muscle mass and strength even after long periods of inactivity.

We’ve known for a while that if you stop using your muscles, they’ll shrink and in time, you’ll lose muscle mass. Until recently, scientists also thought that the nuclei (the cell “headquarters” that build and maintain muscle fibers) are also lost. However, according to a new review, this isn’t the case — and muscles are able to “bank” muscle growth potential

The key lies in a cell called a syncytium — a special type of tissue in which cells are fused so closely they almost behave as a single cell.

“Heart, bone and even placenta are built on these networks of cells,” says Lawrence Schwartz, an author of the new study. “But by far our biggest cells – and biggest syncytia – are our muscles.”

“Muscle growth is accompanied by the addition of new nuclei from stem cells to help meet the enhanced synthetic demands of larger muscle cells,” explains Schwartz. “This led to the assumption that a given nucleus controls a defined volume of cytoplasm – so that when a muscle shrinks or ‘atrophies’ due to disuse or disease, the number of myonuclei decreases.”

The assumption seemed valid for a long time, but it no longer seems to be the case.

Previously, studies have found evidence of nuclei degradation caused by atrophy or paralysis. However, more recent research involving genetic markers found that the decaying nuclei did not belong to muscles — but rather belonged to inflammatory and other cells recruited to atrophic muscle.

In other words, you never really lose these nuclei, and you never really lose your muscle memory.

“Muscles get damaged during extreme exercise, and often have to weather changes in food availability and other environmental factors that lead to atrophy. They wouldn’t last very long giving up their nuclei in response to every one of these insults,” Schwartz explains.

He goes on to quote two recent studies, one in rodents and one in insects, which demonstrated that muscle nuclei are not lost to atrophy and even remain after muscle death has been initiated. This makes a lot of evolutionary sense: muscles get torn during extreme exercise and have to weather changes in nutrient availability and activity variation. Giving up the nuclei every time an unfortunate change happens would not be very productive, Schwartz says.

“It is well documented in the field of exercise physiology that it is far easier to reacquire a certain level of muscle fitness through exercise than it was to achieve it the first place, even if there has been a long intervening period of detraining. In other word, the phrase “use it or lose it” is might be more accurately articulated as ‘use it or lose it, until you work at it again’.”

The study has been published in the open-access journal Frontiers.

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