If you’ve spent any amount of time lifting weights, taken a break for a bit, and then started back up again, you probably noticed that you seemed to regain strength and size much quicker than the first time around.
Well, this isn’t your mind playing tricks on you–the acceleration in progress is a scientifically verified phenomenon often referred to as “muscle memory,” but what is actually going on?
Neurological mechanisms can explain the rapid regain of strength, but not muscle size. Do muscle fibers have some sort of “memory” of their previous, more conditioned states? Or is something else responsible for these effects?
Let’s find out.
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The answer to the muscle memory enigma begins with an interesting fact about muscle cells themselves: they are quite large and one of the very few multinuclear cells in our bodies. That is, they don’t contain just one nucleus but many.
As you overload your muscles with resistance training, new nuclei are added to the muscle cells, which then allows them to grow larger in size. In fact, the number of nuclei within the muscle fibers is one of the most important conditions that regulates muscle size.
Now, if resistance training causes the body to add nuclei to the muscle fibers, which then allows them to grow larger, what happens to our muscles when we stop training for extended periods of time?
I mean…we know what happens in the mirror–we slowly shrivel up and, eventually, look like we don’t even lift–but what happens physiologically?
Well, the answer explains what “muscle memory” really is and how it works.
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It was long believed that, after a having stopped training a muscle for a certain amount of time (“detraining,” as it’s known scientifically), the new muscle nuclei acquired during the training period were lost to apoptosis.
This accounted for the loss of size and strength that occurs during detraining and seemed to make good sense. We now know that’s wrong, though.
It turns out that while detraining clearly results in smaller, weaker muscles, the new nuclei added during the training period are retained for at least 3 months of inactivity. In fact, there’s evidence that these new nuclei are never lost, meaning that resistance training induces permanent physiological changes in muscle fibers.
Simply put: the idea that nuclei are added to muscle fibers as a result of training and lost as a result of detraining is false. In reality, it goes more like this:
This is the why retraining is easier than the first training performed by those with no previous training history, and is the physiology of “muscle memory.”
I find this research pretty encouraging. It’s nice to know that the work we’re putting in now will pay dividends for the rest of our lives.
In fact, scientists believe that “filling up” our muscles with as many nuclei as we can while we’re young can greatly benefit us as we age because a) building muscle gets harder in our later years and b) persistent muscle loss is one of the most serious health risks associated with aging.
Furthermore, while a couple weeks of detraining is enough to slightly reduce the size of your muscles, you can rest easy knowing that a little time off won’t set you back.
Even if life gets in the way and prevents you from training for weeks or even months, you’ll probably find it easier to get going again when you know that returning to your previous state of fitness will be much quicker than the first time. And if you’re able to sneak in a little gym time, you can maintain size and strength with two workouts–or even one–per week.