You will need an assistant for this exercise.
Lie on your back with a buoyancy collar around your neck and a noodle under your hips.
Ask your assistant to place a fin on the foot of your exercising leg.
Ask your assistant to stand behind your head with their hands on your back.
Relax into the water, keeping your back straight.
Your assistant will then quickly push you through the water while you bend your exercising knee.
Keep your back straight and your thigh on the surface of the water.