Like most other exercises, a cross-trainer requires you to keep your stomach and back tight, helping you build core strength. While this doesn’t automatically mean you’ll build a six-pack on an elliptical alone, keeping your core muscles activated will surely help you get in shape. To activate your core even more efficiently, try to let go of the handles. Do this carefully to avoid falling. Using the cross trainer without handles will make your abdominal muscles work extra hard to keep you balanced.