Oscillating hip flexion stretch in supine ("Knee hugs" Hip/lumbar extensors stretch, end range oscillations, supine)

Lie on your back with your legs straight.
Use your hands to hug your affected leg in towards your chest.
You may wish to place your hands behind your thigh, or on your shin.
Hug your knee in towards your chest until it feels a little tight.
Gently bounce your knee in and out in this position.
You can increase the size of the bounce as the stretch starts to ease.