text: Every good exercise program has components of stretching, cardio, and strength training.  You can accomplish the same on an elliptical that you would on a treadmill, but quicker and with low impact (easier on leg joints).  Plus you'll also tone your upper body.  If you want to do crunches there's a safe and effective piece of fitness equipment called a hyperextension (roman chair).  It's great for improving obliques, abdominals, and back muscles.  You don't really say what you're trying to accomplish, so I made some assumptions.