Think of your skeleton as just a bunch of bones held together by muscles and attachments. The length of these attachments and the tone of the muscles affect the entire skeleton's position, or posture. And most people don't realize that sitting a particular way-be it with crossed legs, on your knees, Indian-style, whatever-or doing any one physical act repeatedly can alter the balance of strength from one side of your body to the other. If you did hundreds of pushups every day, what do you think would happen to your posture? If you said you'd get rounded-forward shoulders, then you get the idea. And doing 100 crunches every day isn't going to cut it, either. In fact doing those crunches, especially if you ride a cruiser, will probably give you lower back pain. That's because once again you're creating an imbalance-you are making the front abdominals very strong (or shorter), which will pull on the lower back (antagonist to the abs), eventually causing pain. Crunches and other ab exercises should be part of every exercise program, but more often than not they are only one of a few exercises people do.