Sit up straight on the floor with your legs straight out in front of you.
If it helps, bend the leg you do not plan to exercise and place it where it helps to support you.
Loop a strap or a belt around the ball of your other foot.
A thick resistance band can also be used.
Ensure your knee and toes point directly up towards the ceiling.
Gather any excess
Sitting up tall, tighten your thigh muscle as you pull back on the band.
Allow your heel to stretch away from you.
It may even lift off the floor.
Apply a little more tension to the outer side of the strap.
You should feel a stretch at the back of your knee.
Hold this position.
Relax, and then repeat.