Treadmills have high demands on knees, while elliptical machines do little harm to knees. Then I will talk about the motion characteristics of elliptical machine. Elliptical machine exercises the whole body. In fact, elliptical exercise is also a running type of exercise. Elliptical machine is an aerobic fitness equipment, which can simulate running, cycling, mountain climbing and even more kinds of sports. The main structure of elliptical machine includes handrail, pedal, track, flywheel and control panel. Elliptical machine is suitable for people with bad knees. The elliptical machine simulates the way of human walking by drawing an elliptical trajectory by the machine, which reduces the influence of body weight on the weight of lower limbs and the influence of speed and ground gravity on knees. Although the influence of elliptical machine on knees is secondary in fitness equipment, there are still some, especially when the trajectory of some elliptical machines is not very ergonomic, the heel will unconsciously lift and the gravity of the body will still act on the joints. Recently, Xiao Di discovered an interesting product and adopted some new methods, claiming that it can further reduce the impact on the knee through shock absorption.