This Muscle Energy Technique increase the mobility in your gluteal muscles. Tightness in the glutes can also cause pain or injuries in the hip, lower back or knee so it is important that you try and keep them moving freely.
Lie on your back and lift one knee towards your chest.
Place both hands behind the lower thigh then press your thigh down into your hands (as if you were straightening your leg out).
Press at a comfortable resistance (~20% resistance to start). Make sure your leg does not move and that you relax your head and shoulders.