If you work out in a gym you've probably seen someone doing an exercise with short quick movements, perhaps with too much weight. This is a common mistake that can limit your range of motion and lead to injury.
Range of motion (ROM) is the amount of movement around a...
Do you have a literal pain in the butt? If so, you might be suffering from piriformis syndrome, a type of sciatic pain cause by when the piriformis muscle gets shortened or goes into spasm, putting pressure on the sciatic nerve.
Many people that experience knee pain assume that they have some sort of problem with the bones or ligaments involved. Although this might very well be the case, you shouldn't also rule out the role muscle tightness plays.