Proper body posture is a vital issue for all kinds of exercise. If your body posture is wrong, it may cause some serious problems like back pain, knee pain, muscle injury, etc. So, please maintain correct posture while you ride on your elliptical machine as well as for other workouts.
What you’ll have to do is keep your body straight. Do not go up and down along with the elliptical motion. The proper motion should keep your body steel and move the hands and legs, almost like squats. Keep your back straight, look forward, and paddle.
Here’s a nice video about how you can maintain a proper posture on the elliptical by EverFit Strategies.