Hamstring Curls

Start face up lying on a mat and place your heels right on the peak of the swiss ball. Then tighten your core and bridge up, keeping a straight angle knee to shoulder (do not bend at the waist). Pull the ball back as you breathe out, then back to the starting position keeping the high bridge.

If you can't keep a straight angle and have to bend your waist, slowly work towards this over time.