Muscles don't have memories!!

Peeve: When the scientific community can't agree on a definition consensus for a term, such as 'muscle memory'. 

Muscles don't have memories. Brains do. 

Ask anyone in a gym and you'll get four or more interpretations of what 'muscle memory' is or means. Ask scientists and you'll get one of three; each thinking they offer the only correct definition. 

This was a frequent source of amusement in our lab (neuromuscular pathology); we agreed to avoid the term unless being sarcastic. We often used the general term 'muscle plasticity': the ability of a given muscle to alter its structural and functional properties in accordance with the environmental conditions imposed. That's what muscles do. 

Then, what IS muscle memory?

According to Wikipedia (and a more summarized definition in Oxford Dictionary), 'muscle memory' is:

"...a form of procedural memory that involves consolidating a specific motor task into memory through repetition, which has been used synonymously with motor learning. When a movement is repeated over time, the brain creates a long-term muscle memory for that task, eventually allowing it to be performed with little to no conscious effort. This process decreases the need for attention and creates maximum efficiency within the motor and memory systems."

So, what is muscle plasticity? 

Phenotypic* plasticity allows single genotypes to express different phenotypes under diverse environmental conditions. Organisms, and tissues (some more than others), respond to different environments by changing how they act, look or function. Skeletal muscle is a highly plastic tissue. 

For example, exercise initiates signaling pathways that modify muscle fiber metabolic, physiological and contractile properties of skeletal muscle (sometimes referred to as 'remodeling'). That is 'muscle plasticity'. Whereas exercise can also evoke memories (conscious and subconscious) in the brain of how movements are executed. It is a back-and-forth communication between muscles and the brain via the central nervous system. That is  'muscle memory'.

In language, adjectives connote specificity. In particular, 'neuromuscular plasticity' and pathology were the focus of our research. Muscle plasticity requires the coordinated interaction between neurons and muscles, but pathology narrows the focus. Disease or injury of motor system components, including responsive proteins in muscle fibers, can lead to muscular motor dysfunction. Like all tissues, biological/molecular processes are included. 

One example is muscular dystrophy: a disease in which one or more muscle proteins are absent or dysfunctional because of genetic aberrations that interrupt the signal between the motor neurons and the ability of the muscle to respond. It has little if anything to do with procedural memories, aka 'muscle memories', in the brain. A muscle group without dystrophin won't be able to contract, irrespective of any 'muscle memory' in the brain. 

Using the correct language is imperative for science communication within the scientific community. Incorrect** and vague terms are perpetuated throughout communication and education (formal and informal) outside of that community, such as with medical professionals, trainers, social media, etc. Yet confusion remains if members of the scientific community do not consistently use correct definitions of terms. This needs fixing.

Summarily, the use of the term 'muscle memory' should be restricted to the associations of movement and 'memories' established in the brain. Better yet, these terms are better:

• Procedural memory ( or 'Kinesthetic memory'): the automatic movements involved in throwing a ball, dancing, swimming, steering a vehicle, typing, or even squats.), or
• Motor memory:  process by which animals can adopt both persistent and flexible motor behaviors. 
  
  

MUSCLES DON'T HAVE MEMORIES!
Brains do.

------------------------------------------------------------------
* Phenotypic is the observable traits of an individual resulting from the interaction of its genes (genotype) and its environment. 

** Many researchers have recently published papers in scientific journals and still use the term 'muscle memory' in the context of muscle biology/molecular biology and physiology without ANY reference to -'memories' formed and stored in the brain!