Muscle Memory
Sep 18, 2020
Muscle Memory. Most of us have heard of it, but we’ve also heard about eating meals every 3-4 hours to stoke your metabolism, and that's just straight up broscience garbage.
So what is muscle memory, and is there any science to back it?
What is it:It refers to the idea that it’s much easier to regain muscle mass back that you’ve lost from detraining, than it is to gain new muscle from scratch.
How does it work:
It’s not as simple as your muscles having some vague memory of previous muscle existing and willing it back faster when you start training again, but the ‘memory’ of the movement pattern is part of the picture. Let me explain.
Pre 2010, the main explanation for muscle memory was based on neurological factors, that is, changes that occur to the brain and nervous system. These changes allow you to relearn a task previously undertaken, due to the neural adaptations that occur when initially learning the movement pattern. Avoiding the tired old ‘riding a bike’ example, this is like not having to relearn how to swim every summer, because the movement patterns of your arms stroking the water, your legs simultaneously kicking, and your neck twisting to reach for air just at the right time, have persisted and you can almost pick up where you left off.
It’s also possible that ‘confidence’ and ‘expectations’ in your own ability to perform at a certain level is heightened if it has been previously practised, which may accelerate the rate of progress in the exercise in question. This could cause the individual to perform with more intensity and expose muscles to a greater working volume, which we know is a large contributing factor to muscle hypertrophy. Please note, this is purely personal speculation.
However, I pose to you the ‘4-minute mile example’ to support this personal speculation.
Roger Bannister ran a mile in under 4 minutes which was groundbreaking at the time, in 1954, with many saying it couldn’t be done. Once Bannister proved it could be, it opened up what others believed to be possible for themselves and since then over 500 American men alone have followed suit [9].
Understanding, expanded:
To expand our understanding, we need to run you through some basic anatomy of muscle cells. Don’t let the sciency names scare you off, it should all make sense in a few minutes.
Muscle cells have multiple nuclei (nucleus for plural), up to 100 or more and they can be thought of as the control centres of the cell. Within a muscle fibre, the nuclei are called ‘myonuclei’, and this differs from other cells types which typically only have 1 nuclei per cell. 
We are more or less born with the number of muscle fibres we are going to live with, so enlargement of muscles typically comes from hypertrophy (enlargement of existing muscle fibres) as opposed to hyperplasia (increasing the number of total fibres).
Each myonuclei (the numerous little control centres within a muscle fibre) oversee a specific and limited area and amount of muscle within the muscle fibre, but because the amount they can oversee is limited, this means muscle can’t grow infinitely. The only way to continue increasing muscle size once the maximum is reached is to lay down more myonuclei.
We know this occurs thanks to a study out of Olso in 2010 [2] which used imaging techniques to determine what happened to myonuclei during periods of detraining.
This study found that resistance training causes satellite cells to fuse with muscle cells and these satellite cells also have nuclei which get donated to the muscle cell in the fusion. These added nuclei, now ‘myonuclei’ because they became part of the muscle, allow further hypertrophy of the muscle fibres, and when we stop training, we experience muscle atrophy (shrinking of the muscle).
Interestingly, this study also found that myonuclei in muscle tissue are protected from apoptosis, which is a form of programmed cell death that occurs in multicellular organisms. This means that the new myonuclei created from resistance training stick around when muscle atrophy (shrinking) occurs.
This ‘extra’ myonuclei previously created contributes to the accelerated rate of muscle regain once training recommences after a period of detraining because the formally trained individual doesn’t need to create new myonuclei like a total beginner.
This study however was undertaken on mice, with a more recent 2019 study called ‘Human Skeletal Muscle Possesses an Epigenetic Memory of Hypertrophy’ [3] being undertaken on humans. This study shows that the changes that occurred at the level of DNA (the ‘methylation pattern’) during a training period of 7 weeks persisted during a rest period of 7 weeks that followed. These epigenetic modifications produce new muscle proteins and from this, it’s fair to say that ‘muscle memory’ is written into the DNA of your muscle cells.
Creatine and myonuclei multiplication:
A study published in 2006 named ‘Creatine supplementation augments the increase in satellite cell and myonuclei number in human skeletal muscle induced by strength training’ [4] argues… you guessed it, that creatine supplementation may increase the amount of satellite cells that fuse with skeletal muscle which is a helpful conclusion for those looking to take advantage of this.
While this is an advantageous result for hypertrophy, we are not talking about supraphysiological increases above ‘natural’ expectations. This means that those consuming creatine, although at a potential advantage to those not doing so, are still considered ‘natural’ or ‘not enhanced’.
How long does muscle memory last:
This is a contentious question with no firm consensus, however the previously mentioned ‘Human Skeletal Muscle Possesses an Epigenetic Memory of Hypertrophy’ [3] tested a 7 week rest period on trial participants after a 7 week cycle of training, and they noted muscle memory persisted for the entire duration of the rest period.
However, anecdotally, I’ve found accelerated muscle hypertrophy in clients who have been detrained for much, much longer.
How long does it take for muscle atrophy to occur once training ceases:
Some studies suggest it happens within 2 weeks [7] while others 3-6 weeks [8] however
it is difficult to measure muscle size maintenance, loss & growth as changes to glycogen stores (stored carbs bound to fluid within skeletal muscle) effect muscle size independently to muscle fibres atrophying or hypertrophying.
Changes in glycogen stores significantly effects the perceived muscle size. Various measurements can be used to determine muscle mass gain like looking at FFM (fat free mass), LBM (lean body mass) or CSA (fibre cross sectional area) using DXA, BIA, MRI, or muscle biopsy but these are all effected by muscle glycogen, so the accuracy should be questioned [5].
Final note:
If you’re ‘getting back into it’ after an extended rest with the goal of muscle gain in mind, muscle memory may be on your side. But even if your rest is too extensive to take advantage of muscle memory, this should be no deterrent for kicking some butt. The best we can do is set a realistic plan that has us working at a high RPE above our maintenance volume, and avoid extended breaks again where possible in future.
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References:
[1] Principles of anatomy and physiology, G.J Tortora & R Derrickson, 2009,12th edition, P.305
[2] https://www.ncbi.nlm.nih.gov/pubmed/20713720
[3] https://www.ncbi.nlm.nih.gov/pubmed/29382913
[4] https://physoc.onlinelibrary.wiley.com/doi/10.1113/jphysiol.2006.107359
[5] https://sci-fit.net/detraining-retraining/
[6] https://www.ncbi.nlm.nih.gov/pubmed/10099946
[7] https://www.ncbi.nlm.nih.gov/pubmed/8371654
[8] https://www.frontiersin.org/articles/10.3389/fphys.2018.00744/full
