Rowing machines have the advantage of using the entire body in a single, fluid motion. The seat on a rower slides on rails and there are handles attached to stretchy cords that simulate the arm motion of using a paddle. When performed with the correct technique, rowing spreads the intensity of exercise evenly over all three major muscle groups, legs, arms and torso. Rowers are manual devices. It is a mistake thinking that this machine gives you only an upper-body workout. Because you must push with the legs while you pull with the arms, rowers require all body coordination. They also require you to engage your core abdominal muscles to support and protect your back. Rowers burn lots of calories because they use so many muscle groups. Rowing trainers are not suitable for those of extra weight or exercisers with back problems. Usually extra weight comes with back pain, and this is not a machine you would like to use if you have back issues.