There are so many ways of experiencing Uttanasana, each one resulting in awakening sensititivity in different areas.
In this way, with the belt around the feet and pelvis the belt creates a compactness in the legs and pelvis. The sacrum is drawn in, along with the femur heads - which is very useful for people with hyper-mobility, although all can benefit. This action stimulates the organs of the pelvis, including the reproductive organs. The bones of the legs working against the resistance of the belt is beneficial for bone density.
Place a looped belt beneath your heels, feet together.
Bend your knees a little & tighten the belt.
Slowly straighten the legs, using the resistance of the belt, lifting the buttocks. Keep the hips gripped, lift the inner ankles & knees.
Focus on maintaining the length in the front body, pubice to sternum. Keeping the shoulders away from the ears, press the hands into the bricks & lift your face to aid the dorsal moving in & the sternum lengthening.
If you are pregnant or have a spinal disc problem you should remain in this position & not descend the trunk further.
A restorative way of practising Uttanasana is to have the back against the wall