In a supine position on the floor position the stability ball under your legs between your knees and feet. The further the stability ball is from your hips the more difficult. Raise your hips into the air as you push down into the exercise ball. At the top of the lift your body should be straight on a 30 degree angle with the floor. Hold the position. Pull the physio ball in towards your glutes keeping your hips off the floor. Bring it in as far as possible and slowly release it back to the start position. The exercise is more difficult when you maintain your hips off the floor in between each curl but it might be better to begin by resting your hips back to the floor between each rep until you become comfortable with the exercise.
Stability Ball Leg Curl