Cybex has created a cross trainer called the Arc Trainer that seeks to change the fundamental motion used in most ellipticals. The Reverse Arc Motion moves legs in a biomechanically correct pathway – reducing stress at the knee while offering a complete range of motion for both the knee and hip. The toes are never placed behind the knees thereby reducing patellofemoral compression.
The Cybex Arc Trainer handle bars work in the same motion as your feet do. Basically, as the left foot goes forward so does the left handle bar in a very natural cross country skiing motion. This motion allows the user to work in a more vertical position with less forward lean which reduces loading on the back. This upright posture is achievable because the hip and knees are not forced into extension. A significant effect of this upright posture is that the hip and knee will share the work; as opposed to elliptical trainers where the majority of work is done at the knee joint. The result is less shearing force at the knee joints since the hip is working against an opposing force.
In addition, users commonly report that it is much easier to get their heart rate up using an arc trainer over an elliptical. Studies have shown that since the Arc trainer focuses on exercising larger muscle groups through a complete range of motion, the user will burn more calories and get a better work out in a shorter period of time.
The traditional elliptical motion is fine for most users, provided they invest in a quality product that allows the user to work through a proper biomechanical movement. As well, the user must have proper technique, without too much forward lean which may put undue strain on the lower back. However the Arc Trainer may be a better motion for most users: equally dividing force on the knees and hips and working larger muscle groups through a complete range of motion. The Arc trainer provides the user with natural climbing in a relatively stress free environment as well as the ability to burn more calories in less time and with less perceived exertion.