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Please remember, as with any exercises, to start at a level that is comfortable for you & that does not cause pain.
Hamstring Curls Supine
Lay on floor, place heels on ball with both knees straight.
Use heels to pull ball toward the buttocks. Straighten legs and repeat.
Hip Extension Knee Bent
Lay on stomach over ball with hands and toes touching floor. Bend one knee to 90°. Squeezing the buttocks, raise thigh up until level with upper body. Hold, lower and repeat.