If you haven’t played basketball for years and then you get into a game at your high school reunion and find that after 10 minutes you’re performing like Michael Jordan again, is that “muscle memory”?
Or, you used to workout regularly but haven’t so much as lifted a weight since you had three kids, but then you quickly regain your strength when your new neighbour drags you to the gym, is this “muscle memory”?
Or are you referring to when your body seems to be able to perform complex tasks without the need for you to consciously think about it? For example, swinging a golf club, driving a car, or knitting?
Or are you reminiscing over a delicious bowl of Moules Marinière? Wait no, that’s mussel memory.
The first three are all examples that could be called “muscle memory”. The first and third are actually almost the same thing. Let me explain…
Practice makes pathways
When we practice an activity over and over we develop a neural pathway (a connection inside the brain) for that movement. The more you practice, the more established this pathway becomes. Many of these co-ordinated movements seem to be controlled in a part of the brain called the cerebellum (which is located at the back and looks a bit like a big prune). It could be playing tennis or performing cursive handwriting, but when you stop practicing the pathway starts to degrade. People who come back to a formerly practiced activity often say they feel “rusty”, but after a bit of time spent doing the activity they feel like their muscles are “remembering”. It is more correct to say the nerves in the brain are reinforcing the connection. An established neural pathway is rarely lost completely and practice will help strengthen it again – which is why people say you never forget how to ride a bike.
Many nuclei make light work
In the second case, suppose that you are a weightlifter, have trained really hard and have got very strong. Then you ‘let yourself go’, allowing your muscles to atrophy (or ‘waste away’). Would you be starting from zero again when you returned to training? No you wouldn’t, and here’s why…
Each muscle fibre has many nuclei. Each nucleus has a copy of DNA, and contributes to muscle growth. As you train a muscle, more nuclei develop inside the fibres. The more nuclei, the faster muscle will grow. If you stop working a muscle for a long time, it will shrink in size, but the number of nuclei will stay the same. These extra nuclei mean that it is easier for you to bounce back to close to your former strength levels than if you hadn’t trained previously.
A cerebellum never forgets
In the third case we are referring to implicit vs explicit memory. Explicit memory involves thinking hard about something as you do it. Think about the first few times you drove a car. You were probably hyper-vigilant, scared to death that you’d hit something, thinking about how far to turn the wheel, how much force you were applying to the pedals. After a few months of driving you’re going 100 km/h, adding sugar to your coffee with one hand while texting with the other – putting down the drink only to shift gears. (Don’t do that by the way.)
All those movements have gone from explicit to implicit memory – they have been ‘learned’. The neural pathway inside your brain has become so strong that you don’t have to “attend” to the movements with all of your cognitive horsepower. When something is implicit you can do it and still have plenty of brain space left to carry on a conversation (as before, the cerebellum is important in allowing this). However, even if you are well practiced at something and can do it without thinking, if for some reason you start focusing very hard on that thing, say trying to sink a 12 foot put at mini golf for $100 bet, you might find your performance suffers. My advice is to let your implicit (muscle memory) do its thing. That is why you practice in the first place. Then send me half the cash. You’re welcome.
There are many other aspects of muscle memory – many of which are still being discovered. For a detailed explanation of implicit vs explicit memory I would greatly encourage you to read the book Choke, by Sian Beilock. It is an excellent read with lots of practical tips for helping you achieve better performance under stress.