Hamstring Curls Single Leg

Start by lying on a mat with a swiss ball in front of you. Place your heel on the peak of the ball and come to a bridge position (no bend in the waist) Keeping a straight angle knee to shoulder (if you can) pull the ball back while breathing out. Keep a tight core as this exercise has a tremendous amount of stabilization. If you feel a cramp of other pain in the hamstring stop - you have probably done enough.

Work you way up to this exercise. If you can do about 30 reps of the double leg version in perfect form, then try this variation.

Most people will have trouble not bending the waist at first, but over time your hamstrings and core/back will gain the strength. Great for posterior!