A few weeks ago an ex-student of my department stopped by for a body comp scan and then to have a conversation about training. Currently he is doing some very hard training for his job (going to be a police officer) and is losing a bit of muscle mass due to the caloric demands of the training and not having time to do his typical resistance training. When chatting we touched on muscle memory and I think it is important to explain this to the average person, since it comes up frequently.
Muscles do not have memory
What muscles have is not in fact “memory” like a computer or your brain (and there we are talking about neurological circuits that still science doesn’t fully understand), what they have instead is a very interesting property that no other cell in the human body has. This is that they are multinucleated. This means that one muscle cell thanks to satellite cells fusing to it from hard training, damage, or hormonal activation have more than one nucleus in the cell (plural being nuclei). What is important about this fact is that in your nucleus your DNA is stored, basic biology classes teach you this, thanks to the transcription to RNA and then translation in to protein we can build more contractile units (sarcomeres), more enzymes related to energy production, and more proteins important for cellular housekeeping and structural integrity.
Think of each nucleus in the cell as a factory with a variety of blueprints inside. If we can move more factories in to one given cell we are going to be able to create more products in the same period of time. More production means that we can now build and support a larger muscle
Training increases the number of nuclei you have in your cell and (form the mouse model) they seem to stick around in periods of disuse. This is why it is easier to increase your performance after a long layoff to where you were before you stopped than it was to get to that initial level of performance. Steroids also increase your nuclei so technically after someone has doped they shouldn’t be allowed to compete with natural folks ever again.
The other part of “muscle memory” that people can confuse is the ability to contract your muscles in an organized pattern to perform complex movements. Like the motor control required for me to type this sentence on a keyboard. As you perform a motor patter over and over again you get better and better at recruiting this pattern along with more efficient with the muscles you are recruiting for it. Once you have established a skill well enough you can take time away from it and come back to find your performance though it may have declined it will come back quickly. (Hence why people make comparisons to riding a bike).
This is actually the effects of training on your neurological system. You improve your ability to contract and relax the important muscles in your brain along with get more rapid feedback from sensors and other important neurological units in the peripheral nervous system.
So that is the basics of muscle memory, or really how that is a farce. Hopefully knowing this mechanism will help you understand the caveats of training and science a bit more in this area. Additionally, this is a point to keep you from losing hope when you are laid out with an injury and have to watch yourself atrophy (get smaller). Thanks as always for reading and if you have any questions please feel free to comment below.