This article originally appeared in Well+Good.

Sometimes hip pain, which can also lead to back and knee pain, is the result of your muscles becoming tight and shortened and your joints shifting. Yes, it sounds extreme, but our joints and muscles tend to do their own thing as they get tight and stiff. Case in point: the hip flexors and quadratus lumborum (QL), are often the culprit behind your hips and pelvis shifting, which can result in hip pain.

Why your hips tend to shift into different positions

"When the hip flexors become tight they pull on the pelvis and rotate the pelvis slightly forward into an anterior pelvic tilt," says Theresa Marko, PT, DPT, MS, board-certified clinical specialist in orthopedic physical therapy. One of the easiest ways to tell if you have an anterior pelvic tilt is if there's an arch in your lower back or lumbar spine, your glutes stick out, and your ribs protrude forward.