The elliptical machine can be very useful for older adults or those with arthritis, but for most people it's not a very efficient tool to burn calories. The winner in the caloric expenditure department goes to the treadmill, followed by (from highest to lowest caloric expenditure) the stairstepper (stepmill), the rowing machine, the upright bike, and finally the recombinant bike.
The reality is that, in general, the elliptical machine does not elevate the heart rate nor does it burn bodyfat adequately. This is due to the fact that movement on these machines relies primarily on momentum rather than resistance. Momentum is simply the product of a body's mass and its velocity. Just as in weight training, if you move the joints quickly (increasing velocity), momentum increases while resistance decreases. The net result is essentially less real work being done since less force (resistance) is exerted. Now you know why people like to move quickly on the elliptical machines: it makes the exercise easier!
No matter which machine you choose, be sure not to lean most of your bodyweight on the hand rails for support. These railings are designed for your balance, not for support. By leaning predominantly on these railings, you'll reduce your caloric expenditure because your lower body will not be working as hard as it should. Straighten your posture by pulling your shoulders back and looking straight ahead. Rest your hands lightly on the rails to get an optimum workout. If you still cannot resist leaning heavily on the rails, you need to reduce the intensity on the machine--you're pushing way too hard. On the other hand, if you can read a book or comfortably breathe through your nose while doing cardio, your intensity level is way too low. Step up the intensity!
BOTTOM LINE: if you want to burn serious calories, you have to work hard to do it--sorry, working out on the elliptical machine does not qualify, in most cases, as hard work. Get out of your comfort zone and hit the treadmill, stairstepper or rower instead.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."