Muscle Memory

What Is Muscle Memory?

We all know that if you lift weights and stop lifting for a few months (3-6 months), you will eventually lose strength and muscle. However, if you start training back again, you will gain back the lost muscle or strength within a few weeks- as if the muscle remembers where you left off. This phenomenon is called muscle memory.

Past

We used to believe this is largely due to the nervous system mechanisms in our body. Well, the nervous system mechanisms may explain the strength gains, but it doesn't explain how you can gain back the muscle size so quickly. 

But recent studies show that we might have finally solved the mystery of muscle memory.

 

How did they solve it?

Unlike other cells, muscle cells have more than one nucleus (probably thousands). So why do muscles need so many nuclei? This is due to the fact that nucleus is basically what controls the cell and since your muscle are a lot bigger and way more complex than other cells in the body, one or two nuclei just won't do the job. So, when your muscles get bigger, you have to add more muscle nucleus. The increase in nucleus with muscle growth has been shown in quite a number of studies. It has been shown that people who take steroid and people who grow muscles easily have a lot more muscle nuclei than normal people do. 

Just like muscle growth, we believed that when we lose muscle, the opposite happens- we lose some muscle nuclei since there is no reason for the extra nuclei to sit around. This was also supported in studies which showed as muscle shrinks in size, the number of nucleus decreases too. 

Now here comes the surprise. 

However, recent studies using different animal models showed that as muscle atrophies or shrink due to inactivity or detraining (until 3 months), there is no loss of muscle nuclei as we previously thought! As shown in the picture below, the muscle size decreased b 50% (lines) but the muscle nuclei count (stained with green dye) remained the same.

Since now the muscles has the same number of muscle nuclei after we stopped training, it is relatively easy to build the muscle back to its previous size. So these muscle nuclei seems to acts like 'memory cells' due to the fact that they know how much muscle you had before you stopped training. 

But why did we think muscle nuclei die with muscle loss?

The recent studies used a different approach and technique to study these nuclei. In previous studies, they were actually counting nuclei which belonged to the connective tissues and other cells (satellite cells) and these nuclei do in fact die with detraining. So researchers mistakenly assumed that the muscle nuclei die with muscle loss. But these weren't actual muscle nuclei as the missing nuclei are those belonged to the connective tissues as explained above. The recent studies only counted the actual muscle nuclei and showed no loss.