I think a lot of these kinds of problems arise because people generally do not learn how to relax muscles and selectively engage only those necessary for the mo

I think a lot of these kinds of problems arise because people generally do not learn how to relax muscles and selectively engage only those necessary for the movements they make. The human body has more degrees of freedom than it needs to accomplish the tasks of daily living - you can, for example, awkwardly walk with everything below the hip locked in place (it looks like a penguin waddle). If you can't do things one way, you can often contort yourself to do them another. How does this cause muscular weaknesses and imbalances? If a strong muscle is pretty much always tensed up, you plan out motor sequences that avoid using the opposing one. This muscle will naturally wind up becoming weak, but that's not really the fundamental problem. It's more that you use too much of the wrong muscles to do things. The process for learning these skills is not particularly well documented in my experience. I think this sort of thing is the core idea behind both Alexander Technique and Feldenkrais Method, but I haven't read/experienced them in depth and aren't certain about it. Both of these are mostly transmitted through (sometimes literally) hands-on tutoring. I personally picked this up through getting into Blues idiom dancing, and probably got some of the previously mentioned stuff second or third-hand. "Progressive Muscle Relaxation" is also probably relevant?