Think of your body like a car. Where the muscles are the shock systems in the car and the joints/bones is the frame of the car. The job of the shock system is to absorb any force that is required to not “bottom out” on the frame of the car. Example: when you go over a speed bump, the shocks in your car are supposed to absorb that force and prevent the frame from taking any damage. This is the same job of the muscles in the body. When you perform an action, whether it is playing sports or sitting at a desk for a job, the muscles should be working to absorb the weight and stresses so that you don’t ‘bottom out” or rest on the skeleton frame for an extended period of time.
So when you are in pain or get hurt, for the most part, the main reason is that the muscles (shocks) didn’t respond fast enough or too weak to prevent the injury. This is the same reasons out hear people say, “I get massages, go to the Chiropractor and/or stretch all the time and it seems to help but keeps coming back.” Or “I took (said extended period of time off) and it still didn’t help and I have the same pain!”
The key component that is missing from most therapy programs is the strengthening aspect. Your sympathetic nervous system is responsible for the “fight or flight” mechanism and it will do whatever it has to do to get the job done and survive. In this process the brain will shutdown/activate/tighten any muscle it needs to, to prevent damage to the frame of the skeleton.
Not to get too technical, but flexion/tightness of a muscle is the sympathetic nervous system activating to prevent you from doing any more damage and the only way to tell the brain to turn off the protective mechanism and say “relax” is by strengthening whatever muscles (shocks) failed and caused the damage in the first place.