Rhythmic stabilisation - perturbations to knees (Core/abdominal stabilization, perturbations to legs, supine on floats)

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.
Your assistant shall then apply a sudden gentle pressure through one of your knees in the direction of the floor as you attempt to resist any movement by using your stomach muscles.
Your assistant shall continue to apply sudden pressure to each of your knees at random.
Repeat.