How strong is your core? If you've tried any exercise program, or watched the infomercials, you've probably heard a lot about developing "core strength." Generally, while a lot of us might only think "abs," this refers to strengthening the muscles between your pelvis and shoulders. Your core supports the rest of your body, protects your spine and is at the root of daily muscle activity. Arthur Agatston, M.D., cardiologist and author of the South Beach Diet, recommends core strength training for more than physical fitness, but also for strengthening your heart.