http://AskTheTrainer.com Michael Behnken, MS, NASM-CPT-PES, CSCS San Francisco Based Personal Trainer The BOSU Ball Supine Bridge is a great beginning core exercise. It teaches gluteal activation for people with weak or lengthened glute muscles. If you feel this exercise significantly in your hamstrings, you need to stretch your biceps femoris. Do not arch your back at all during this motion or any core exercises. Maintain the drawn in maneuver for the duration of the movement. http://fitSF.com San Francisco Personal Training