A Life Fitness Leg Curl is classed as a Selectorized piece. Selectorized units are strength machines that have a weight stack, typically ranging from 100 - 500 lbs, in which a specific increment weight can be selected. The particular weight is usually selected with a pin, which permits a number of resistance options, thus allowing a vast range of users, from beginners, to more advanced, to obtain a beneficial and progressive workout on a single machine.