Restricted mobility will be caused by one or both of two major factors: lack of joint mobility or lack of muscle flexibility
In the case of lack of joint mobility, the joint capsule is restricting movement. This issue will most often present with a feeling of intense tightness, pinching, or pain that is deep in the area of the specific joint. At the same time, the lack of mobility will not likely allow any of the surrounding muscles to reach a full stretch.
For lack of muscle flexibility, there are actually two possible causes. One issue may be that the muscle, itself, is short. However, this problem is extremely uncommon. The more likely issue is a muscle that is chronically hypertonic or overactive. In this case, the muscle is constantly in a low-grade contraction, and so you are not reaching the muscle’s full length. Instead, you are fighting against a contracting muscle.
Basic, static stretching will never release the tension or improve the muscle’s flexibility if the issue is chronic hypertonicity. Instead, you must decrease the activation of the target muscle. The best ways to achieve this goal are through post facilitation stretching or PAILs/RAILs.