Common sense will tell you that musicians (and athletes, dancers, or anyone who focuses on one human activity the majority of the time) will experience muscle imbalances at some point in their life or career. They might not label their pain or adaptation as a result of muscle imbalances, but it's often at the root of our issues. Let's backtrack first though.
Muscles move bones through a combination of contraction and relaxation in tandem with opposing muscle groups (i.e. the hamstring group and the quadriceps group or opposing groups). Contraction is also called facilitation, and relaxation as inhibition. In the gait cycle, the hamstrings will contract to extend the hip and flex the knee, whereas the quadriceps will contract to extend the knee and flex the hip. They work in opposition at various points in walking. (*Just to be clear, there are many other myofascial units that play a role in gait. This is just a simplified example!) Normal muscle function is when the facilitation/inhibition cycle is balanced, with no one muscle or muscle group dominating above the others.
Imbalance is when a muscle or muscle group dominates within its role in movement. This may be due to overtraining, meaning that the opposite muscle may be weak, with limited range of motion, or have difficulty firing. If we apply this to walking with hamstrings and quadriceps, many people over-fire their quadriceps, meaning that they don't relax after their work is done. This may then pull on the knee cap (patella), affect the resting length of the hamstrings, and also affect movement actions like walking, extending the hip, etc. This uneven relationship may be because of overtraining (i.e., way too much quadricep strengthening, lack of hamstring mobility or strength) or a combination of other factors.
What makes this issue more interesting, at least to me, is that it's not just a muscle issue. Our nervous system plays a huge role in the way we recruit muscles and retrain them. For example, a trauma to the tissues (accident, injury, etc) can affect the muscles long after the injury has passed. Speaking from personal experience, I injured my knee in a bike accident 8 years ago, but my non injured hip and leg do weird compensations, even though the other leg is perfectly capable of healthy movement now. Physical and emotional trauma can also take on an emotional/fear response- a past injury or emotionally traumatic event may evoke a sense of fear, albeit unconscious, when addressing that muscle. Musicians who have experienced tendonitis in one arm or hand may have this sense when beginning to rehab, practicing a challenging passage, or receiving massage/bodywork. This can also apply to more complex traumatic events like assault, physical violence, car accidents, and other events, which may force the person to dissociate from their body or areas of the body. All of this can be labeled as a neuromuscular imbalance, which is more complex than simple "muscle weakness/strength" models.
Putting it all together, when someone comes in with a pain symptom, either related to music or other events, it's a lot more complicated than "you're practicing too much" or "your instrument setup needs to improve." Imbalance can be a result of
1) Exercise/overtraining: musicians often overtrain the flexor muscles of the hands and forearms with little attention to larger muscle groups or opposing actions
4) Neurological disorders
5) Illnesses: arthritis, diabetes, chronic fatigue, and many other illnesses affect muscle tension relationships, pain, and strength.
6) Pain: Pain will affect the nervous system's ability to know where it is in space (proprioception) and will affect movement. There have been quite a few good blogs on pain and movement, so here is one from guest writer, PT Arlyn Thobaben, to get started.
7) Stress: Stress, along with pain, can affect muscle tensional relationships. Often when we're stressed, we move and breathe in a less than optimal way, which may enhance tension in the upper back, neck, and so forth.
How can we address these issues? Bodywork, especially with someone who can address muscle imbalances and nervous system imbalances can be a great starting point. General exercise can make imbalances worse if not addressed- seeking a knowledgeable trainer in pilates, corrective exercise, weight training, or other movement modalities can help restore balance to overworked muscles. As I mentioned in the last post, everything starts with awareness, so finding a teacher in subtle body practices like Alexander Technique, Body Mapping, Feldenkrais, or other practices can be very helpful in feeling the imbalances in your own body. Lastly, giving your nervous system the chance to relax, whether through constructive rest, massage, or meditation is a great starting point for moving out of the fight and flight sympathetic nervous system response.