How does muscle memory work for bodybuilding?

Luke Tulloch

What is muscle memory?

There are two different things that people call muscle memory. The first is a skill-based concept – how long will it take to develop reflexes for basketball? This involves practicing a movement until it feels like second nature, and while it’s kind of relevant to complex lifts in the gym, we’re going to focus on the other commonly used definition.

The second idea is what we’ll talk about here, and that is how muscles can grow back to their original size surprisingly quickly after a period of detraining.

When we stop lifting weights, muscle size and strength goes down over time. You’ve probably noticed that it’s much faster to get back your size and strength when you start training again, and this is what muscle memory refers to – it’s as if the muscles ‘remember’ what size they used to be.

Is muscle memory a real thing?

Muscle memory is absolutely real. We can explain it mostly through myonuclear domain theory (don’t be scared, it’s actually simple to understand). Anecdotally, many high-level bodybuilders and powerlifters take some time off completely every year, usually after competitions. Personally, I don’t really train when I go on holiday.

In fact, I think for recovery purposes and as a mental refresher it’s probably a good thing to take at least a couple of weeks completely off each year.

Here’s another personal story. Sometime around 2015 I had the opportunity to do an adult gymnastics seminar and since my physique training was feeling a little stale at the time, I decided to spend the next 6 months exclusively doing gymnastics- style workouts.

I still trained 4-5 days a week, but the exercises were far more skill based and didn’t provide the same type of stimulus for muscle growth, especially to my legs – which happen to be my strongest muscle group.

Over this 6-month stint I went from around 97kg to 91kg (213lb to 200lb). When I returned to bodybuilding, I stunned newer members at the gym by gaining back the weight over about 2 months – quite a stupendous transformation, especially if you didn’t know where I started!

Here's a pic of me after I gained back most of my weight:

How fast do you lose muscle?

When you stop training, both strength and muscle size shrink. Maximum strength has a couple of components: muscle fibre size and coordination of muscles by the nervous system (this is actually quite similar to any other coordination skill you can develop such as throwing a ball or playing a musical instrument).

Over the first week or two of ceasing training, we see some small decreases in max strength that are probably because of degradation in muscle fibre coordination – you just get a little rusty at activating all your muscle fibres.

After a month or so, we start to see the effects of reduced muscle fibre size. As the muscle shrink, their ability to produce force also decreases. This is in conjunction with more rustiness setting in.

An important sidenote: since it takes 2-4 weeks to see any noticeable changes in muscle mass, don’t worry if you go on holiday and can’t train like you normally do. You probably won’t lose much, and if you do make sure you keep reading (it’s easy to get it back).

Why do you lose muscle when you stop training?

Muscle fibres are super responsive to loading. If we provide mechanical tension on the muscles by being physically active or by lifting weights, they respond quickly and start to grow – but once that stimulus is gone, they’re equally responsive in letting go of gains.

This is because it’s expensive for the body to keep muscle around if it doesn’t need it. It costs energy and amino acids from protein to build and maintain large structures like muscle fibres, and if they’re not really being used to ensure survival the body recognises that resources are better spent elsewhere.

How and when does muscle memory develop?

I mentioned myonuclear domain earlier, and now I’m going to explain it because it explains how muscle memory works.

Myo- comes from Greek and means ‘muscle’

-nuclear refers to the nucleus of the muscle cell (muscle fibres and muscle cells are the same thing).

Remember back to biology class where you learned that the nucleus is where we store all our DNA. This is the command centre; it runs the day-to-day tasks and provides recipes for building different components of the cell. It allows protein synthesis to occur and makes us more resistant to muscle damage.

Now, muscle cells are huge compared to other cells. And just like a city can’t grow bigger and stay functional without more hospitals, police stations and power plants, a cell can’t grow bigger without more command centres to manage the extra area.

We call the specific area a nucleus looks after in the cell the “myonuclear domain”.

Luckily, muscle cells are unique in that they can have multiple nuclei/command centres. Most cells are limited to one nucleus and this provides a hard limit to how big they can grow – just like a city with a limited electricity network.

Therefore, the more nuclei there are the larger the potential size of a muscle fibre.

And although we lose muscle size fairly quickly after ceasing training, we retain any additional myonuclei we’ve accrued for a much longer period and this gives us a huge advantage when we get back to training again. It means instead of having only one command centre overseeing muscle growth, we have several that can all work together at the same time.

All the dark purple spots in this picture of muscle are nuclei:

How satellite cells aid muscle memory

So clearly, we want more myonuclei. But how do we add more to the muscle fibres?

The mechanism involves a type of cell called satellite cells. These are cells that sit just outside the muscle fibre itself for the express purpose of helping recovery from training (as far as we know).

Satellite cells are activated by exercise and can help repair muscle damage, but most importantly they can change into muscle stem cells, which then donate their nucleus to the muscle fibre.

This means that over time, regular resistance training results in a steady accumulation of more myonuclei and this allows us greater potential for growth. It’s also the primary contributor to the muscle memory effect.

Is muscle memory related to muscle soreness?

Possibly, to some extent. Muscle soreness is not perfectly correlated with muscle damage, but there is some relationship there. Any type of exercise can increase the pool of available satellite cells, but to get them to differentiate into muscle stem cells and donate their nucleus, we need to have some degree of muscle damage occurring.

I don’t think this means we should specifically try and induce muscle damage with training. If you’re training hard to try and grow muscle by putting tension on your muscle fibres, muscle damage is going to come along for the ride regardless. Actually, this helps bolster the argument for full range of motion – full ROM causes more muscle damage than partial ROM and could partly explain why we see better muscle growth over time with full ROM training.

Inducing too much muscle damage can make it difficult for the body to synthesize enough protein to both repair the damage AND grow. Digging too deep a hole by chasing muscle damage is probably not a good idea, and since muscle soreness is not a perfect proxy for muscle damage, chasing soreness to try and get more nuclei into your muscle fibres is probably not going to work out.

Muscle Memory with steroids

Satellite cells and muscle memory also have a role to play in the effectiveness of anabolic steroids. Anabolic steroid use seems to increase the number of myonuclei in the muscle fibres, which would potentially elevate the ceiling for how big muscles can grow by enhancing myonuclear domain. It also has implications for drug cheats in sport – using steroids enhances trainability even after cessation of use since you have more nuclei sticking around supporting protein synthesis in the muscle fibre.

Some people also seem to just have more nuclei in their muscle fibres, and this might be one aspect of genetics that can help certain individuals grow like weeds.

How long does it take to get back in shape?

The answer depends on how long you’ve been training and how long you’ve had off. While we need more research to get a better understanding, some research suggests that myonuclei that are added to muscle cells can hang around for as long as 15 years. Anecdotally, I wouldn’t expect all your gains to come roaring back after over a decade without training but unfortunately, we don’t have a solid answer for exactly how long is plausible to be away from training and still get a strong muscle memory effect.

It does take time in the first place to accrue myonuclei, though. At the start of your lifting career, there are obviously less nuclei in your muscles. As you continue to train, you become more resistant to muscle damage and this is at least partially explained by the addition of more and more myonuclei over time.

This is part of the repeated bout effect – resistance to muscle damage occurs the more you train. It means that I’d expect a more advanced lifter to have a stronger muscle memory response than a beginner, but I can’t be more specific than that as it will depend on the specific context of each individual.

Summing up muscle memory

Muscle memory is not a myth! It actually has a solid biological explanation and it’s an active area of research. The practical takeaways are that you need not worry about having the odd lay-off from training, whether that’s due to psychological burnout, wanting to try something new, vacation or injury. It means you can get your size and strength back to where it was pretty quickly.

Thanks for reading,

Luke.