The elliptical is awesome in so many ways, but it's also easy to cheat on this joint-friendly machine. Avoiding the handles [1] at different points of your workout will engage your core, but when the hands go, form often follows. Get more out of your elliptical workout with this simple trick.

Without the handles our bodies want to shift from side to side, rather than propel forward. Even if your arms are pumping, your hips may bounce from left to right, and while your heart rate stays up your quads are getting a break. When you're doing intervals with no hands, place your hands firmly on your hips for 15 seconds and pull your shoulder blades together to maintain posture. You will feel your hips move less, your core tighten, and your quads challenged. Repeat whenever you feel your form slipping.

Source [2]