How Muscle Memory Causes Chronic Pain
The idea that your body will inevitably break down as you age is a myth perpetuated by the medical community. As a result, many people experience muscle and joint pain and never ask why—or if it might be avoidable.
While there are many causes of pain, including autoimmune diseases, cancer, and neuropathy, most pain and degeneration occurs because of the way that we habitually use our bodies. For example, in the case of back pain—the most common type of chronic pain, experienced by up to 80% of Americans at some point in their lives—it’s estimated that 97% of cases are mechanical in nature. The way we sit, stand, and move makes our muscles chronically tight and sore, compresses our joints and nerves, and puts stress on our bones and connective tissue, often to the point of causing significant pain and damage to the structure of our bodies.
All of these painful problems are the result of muscle memory: your nervous system’s way of making movements automatic and efficient. You may not be aware of it, but your nervous system is constantly reinforcing old movement patterns and learning new ones.
For the most part, acquiring muscle memory is enormously beneficial. Without muscle memory, you’d spend all day figuring out how to brush your teeth and get dressed for work.
Unfortunately, this automatic learning process allows you to develop unnatural and damaging muscular habits too. For example, if you choose to sit slouched forward at the computer every day, your nervous system will start keeping you in that posture by subconsciously contracting your abdominal and pectoral muscles. Soon you’ll be sitting and standing with slouched posture all the time, even when you’re not at the computer. For most people, this slouched posture is not a genetic condition or an inevitability of the aging process; it’s simple muscle memory.
Functional magnetic resonance imaging (fMRI) shows that when we first learn a movement, our prefrontal cortex (an area of the cerebral cortex that plans complex behavior, makes decisions, and focuses attention) is highly interactive with other brain regions. As we practice the movement over and over, the prefrontal cortex becomes less involved, and activity increases in the motor cortex and basal ganglia (a subcortical cluster of neurons that plays a role in learning, memory, voluntary motor control, and habit formation). This shift correlates with decreased need for conscious attention as we master the movement. Ultimately, our long-term motor memories are stored in the vestibular nuclei in the brainstem.
When repeated muscle contraction is signaled by the brain, muscles retain excess tension. A sensorimotor feedback loop in the nervous system called the gamma loop automatically regulates the level of tension in our muscles. As the brain continues to send the same messages to contract, the baseline level of muscle tension being set by the gamma loop gradually increases. Our proprioception (our internal sense of our posture and body position in space) adapts so that the increased level of muscle tension feels normal.
We’re usually not aware of this gradual tightening until our muscles become stiff, then sore, then downright painful. Tight muscles also pull our skeleton out of alignment, causing poor posture and issues like functional leg length discrepancy, idiopathic scoliosis, movement limitations, and recurring injuries in athletes. The misalignment and pressure caused by tight muscles also leads to joint degeneration and nerve impingement, like sciatica.
We each develop unique patterns of muscle use and tension throughout our body as a result of our repetitive daily activities, our reactions to stress, our personality, the injuries we sustain, the sports we play, and any physical training we engage in. No other human being on the planet stands and moves quite like you.
A study published in the Journal of Applied Physiology in October 2019 calls these muscular patterns our “individual muscle activation signatures.” The study found them to be so predictable that a computer program could recognize patterns of muscle activation in individuals 99% of the time.
The study authors recognize recognize that the concept of individual muscle activation signatures has implications for understanding why people experience musculoskeletal pain and degeneration:
“This would open new research perspectives in which individual differences are considered relevant information for addressing fundamental questions about the control of movement in health, aging, and disease…It is known that even small differences in activation level can have a large effect on movement. It is, therefore, possible that each individual muscle activation signature has specific mechanical effects on the musculoskeletal system. As such, some strategies may place some individuals at greater risk of developing musculoskeletal disorders than others.”
Athletes, dancers, and other trained movers have long understood the uniqueness of our muscular patterns. Many of the comments to the New York Times article on the study agreed that the finding was old news. However, while the fact that we all stand and move differently is obvious to most of us, knowing how to change these deeply learned muscular patterns is not widely known—and this is why so many people suffer in pain.