In principle what we call "Muscle Memory" is the ability acquired through the constant repetition of sequences and actions, to perform the same actions automatically, minimizing the need to be alert to action.
A classic example is to drive a car: knowing the path (and unless someone cuts our way bringing our conscience to have to re-emerge to intervene like a spring) it will often happen that you arrive at your destination completely lost in your thoughts and not having you almost realized you had driven the route.
Tutto this is possible thanks to the extraordinary abilities of our mind which over time has optimized the ability to adapt and learn new patterns by modifying the structure of the brain itself, creating new neural pathways for each concept and procedure acquired.
An important premise should be made: our brain is unable to discern between right or wrong practice but will acquire the pattern regardless if repeated. If you perform the exercise incorrectly and continue to do it for an unspecified number of times, you will acquire the movement incorrectly and then you will hardly be able to change it.
In Athletics Practice?
How does this relate to sports practice?
The fact that we are talking about muscle memory should not deceive us into believing that there is some cognitive capacity of the muscles: in the muscles there is no nervous tissue capable of storing memories or patterns, everything starts from the nervous system that records the movements and creates new neural connections to define that path that become more solid and precise with the repetition of the executions.
The term "muscle memory" in sports, and especially for what concerns Bodybuilding, refers to that phenomenon whereby once the mental schemes have been acquired, even after a period of prolonged training, Once back in training, the gains in hypertrophy and strength are much quicker and easier than achieving the same adjustments the first time around.
Also following significant muscle atrophy, muscles that had previously undergone an increase in volume and performance regain these qualities faster than normal thanks to the fact that the previously enlarged muscle sheaths will be able to allow more space for muscle growth.
Evidence has shown that strength gains occur well before muscle hypertrophy, and the decrease in strength caused by de-training for a prolonged period precedes muscle atrophy. To be precise, strength training increases the motor excitability of the neuron and induces synaptogenesis, both of these conditions would help improve communication between the nervous system and the muscles themselves, increasing the perceived strength for the same mass because it is simply the brain. who learns to make better use of the available muscle, managing to enlist a greater number of muscle fibers with each execution.
However, neuromuscular efficacy is not altered in a period of two weeks after the cessation of use of the muscles, it is simply the neuron's ability to excite the muscle that decreases in correlation with the decrease in strength. This confirms that muscle strength is first affected by the neuronal circuit, rather than by external physiological changes in muscle size.
A study that observed fiber type conversion during muscle hypertrophy may have uncovered one of the possible mechanisms of muscle memory. In this study, a group of sedentary adults were analyzed for the distribution of myosin heavy chain isoforms (MHC Myosin Heavy Chain), the composition of the types of fibers and the size of the vastus lateral muscle fibers before and after 3 months of resistance training and then again after 3 months of non-training.
After the weight training period, the MHC IIX content decreased from just over 9% to 2%, with a corresponding increase in MHC IIA (42% to 49%). After the non-training period, the amount of MHC IIX reached levels higher than before and during resistance training, over 17%! As expected, significant hypertrophy was observed for type II fibers after resistance training and even after 3 months of non-training the fibers remained larger.
MHCs determine how muscle fiber works e they are the ones that make a "fast twitch", "slow twitch" fiber or something in between. Some MHCs are known to undergo a transformation in response to weight training. In this case, the fibers that contain the MHC IIX are fibers of which it is not known for certain which type they belong until they are called into action. Once recruited, they become MHC IIAs.
Thus, fibers that contain MHC IIX proteins act as a reservoir for muscle hypertrophy as it were, because they can transform into fibers that contain MHC IIA and which grow easily in response to training. This study showed that resistance training decreases the amount of MHC IIX while simultaneously increasing the content of MHC IIA.
This was expected, but what they did not expect was that non-training following heavy resistance training seems to cause what they call an "unexpected increase" or a duplication of the percentage of MHC IIX isoforms, significantly higher than that measured initially. What does this mean? It could mean that after a break from training there are more fibers available for hypertrophy (growth) than there were before starting to train. In a nutshell, this could very well explain the effect of "muscle memory" experienced by many.
The best example of muscle memory is represented by bodybuilder Casey Viator, who in 1974 following an accident (he lost a finger at work and due to an allergic reaction to tetanus and seriously risked dying) did not train for the next 4 months and changed food (he went from 1500 kcal to 950 kcal) lost over 4 kg of weight and mass in 15 months, going from 90 kg to about 75 kg, with a fat mass of 19%.
In the following month, under the supervision of Dr. Plese of Colorado State University, he performed 14 training sessions (training every other day) came to weigh 96 kg, increasing his body weight by 20 kg and decreasing his fat mass by about 8 kg (he reached a body fat index of about 7,5%) for an overall gain in lean mass of 28 kg.