Stand on your right foot, keeping it flat on the ground throughout the exercise. Keep your left leg straight and extend it in front of you. Drop as low as you can into a squat. If your right knee moves to the inside of your right big toe, then you likely have tight adductors (inner thigh muscles) and weak abductors (muscles that pull your leg outward), including your gluteus medius (a buttocks muscle that helps keep you stable during single-leg movements). Perform the test on your left foot as well.
