We use the term “muscle memory” quite often, but are not entirely clear about the true meaning of the topic. If we understand it in simple words, muscle memory is a type of memory that unconsciously helps us to perform various motor tasks that we have somehow learned through daily habit, either through intentional training or simply as a result of informal, unintentional or even unconscious learning from repeated previous experiences.
In scientific terminology, we call this memory “procedural memory” or “motor memory” because it allows us to perform various motor tasks/procedures or skills automatically or spontaneously, without any conscious and conscious effort as to how the procedure should be followed, and without any proper calculation of how to identify and achieve the different steps of the procedure and how to proceed from step to step.
Classic examples would be walking, cycling, driving, swimming, tying shoes, playing a musical instrument, etc. If closely observed, these are extremely complex skills that require time to learn and master. They require coordination of the senses and muscle activity. When you practice these skills over time, these skills or the patterns associated with them slowly become embedded deep in your central nervous system (CNS).
By practicing certain activities such as walking, swinging a tennis racket, playing a piece of music on the piano, or driving a car, we learn to perform these complex and coordinated activities with little or no input from the part of the brain that controls voluntary, voluntary muscle contractions – the brain's primary motor cortex.
Once a movement pattern has first been learned in the motor cortex, it is transferred to the basal ganglia deeper in the brain. Consequently, it is possible for people to perform complex coordinated movement patterns without paying little or no attention to them and perhaps even thinking about something else entirely.
Thinking in these terms, the concept of muscle memory as it relates to movement seems pretty simple: memorized movement patterns are stored in and released from the brain's basal ganglia.
However, this is a completely different phenomenon than what we understand when we talk about muscle hypertrophy and strength. This is why the term “muscle memory” can be a bit confusing.
The phenomenon that “skeletal muscles may have some kind of memory” comes from human observations showing that previously trained individuals gain muscle mass and strength more quickly when retrained. This phenomenon was first observed in a 1991 study that showed that women regained muscle strength and muscle fiber size just as quickly during six weeks of retraining as they did during the first 20 weeks of strength training.
However, there is no known mechanism for memory in muscle cells, and to date the long-lasting effects of prior training have been attributed to motor learning in the central nervous system. However, it has been reported that muscles can remain hypertrophic even after several months of withdrawal.
For example, a 2003 study found that strength gains from two years of resistance training in older people were not completely lost even after three years of off-loading.
Let's try to understand the reason for this. Muscle cells (or muscle fibers) contain hundreds to thousands of small nuclei/myonuclei. The nuclei/myonuclei are small control centers that enable the rapid and coordinated growth and repair of muscle tissue.
Sustained muscle hypertrophy requires the formation of new nuclei by muscle stem cells (satellite cells). More nuclei mean more efficient growth and repair signals required to adequately meet the needs of the growing cell/muscle fiber. As the muscle size increases, the number of nuclei increases.
We also have to remember that our muscle cells cannot produce nuclei. Instead, they take it from a different type of cell, called a stem cell. Stem cells are special cells that can develop into many different cell types in the body.
There are many different types of stem cells in the body, but the types that are most involved in muscle growth are called satellite cells. These cells rest near muscle cells and are recruited when needed to help heal and repair damaged muscle fibers.
Once called upon, satellite cells attach to damaged muscle cells and donate their nuclei, aiding in repair and increasing the cells' potential for greater size and strength. (This is one of the processes that causes your muscles to get bigger and stronger when you lift weights.)
It was originally assumed that these nuclei were lost during muscle atrophy. However, it turned out that previously added cores are more durable than previously thought. Sure, muscle fiber size decreases with no training, but the extra muscle nuclei from periods of concentrated growth and strength training are retained for a long time.
A 2013 animal study showed that nuclei gained during overuse hypertrophy are not lost during three months of muscle atrophy, when the muscle returns to its original size. Although muscle size decreased during this period of inactivity, the number of nuclei did not decrease.
This is great news because it's like a long-term investment in strength. Otherwise, it would be a total waste of resources for your body to make more nuclei only to lose them all through a little deprivation.
However, it is still not clear how long these cores actually remain. However, studies have shown that muscle memory lasts for several years. In the skeletal muscles, the length of memory is at least 15% of the average life expectancy (approx. 80 years). That is, hypertrophy occurs at least 12-15 years after cessation of physical activity.
Studies have now shown a very strong genetic connection to muscle memory. Stages of skeletal muscle growth are “remembered” by the genes in the muscle, helping it grow larger later in life. Researchers examined over 850,000 sites on human DNA and discovered the genes that help muscles grow after exercise, then return to normal, and grow again later in life after exercise.
This is also why it is harder for someone who has never exercised to start building muscle later in life than it is for someone who has exercised, taken a break, and then started again.
Another question that often comes up when it comes to muscle memory is: How long does it take to build muscle memory? Now the answer to this is not entirely clear. But in general, consistent training for hypertrophy and strength, 3-4 times per week for 4-8 weeks is a period of time we can consider.
Of course, muscle memory improves the harder and longer you train. This is why a person who trains consistently hard for years can rebuild muscle much more quickly after a period of training.
However, the entire core theory was recently called into question when a meta-analysis study found that skeletal muscle hypertrophy was associated with higher myonuclear content, which was preserved with atrophy in rodents, but not humans. In humans, sarcopenia was associated with lower myonuclear content.
