During this exercise, keep your back straight and in neutral alignment, and pay special attention that you don't arch your back. Use your muscles to create a slow, controlled movement — do not swing your legs.
You can also add fire hydrants to the mix as well for more hip flexor rotation. Instead of lifting your leg back, lift it to the side, so your thighs are parallel to the floor and the soles of your feet are facing the wall behind you.
Source: POPSUGAR Studios