Nautilus originally derived its name because their first off-center pulleys resembled a chambered Nautilus shell. The cams on the older Nautilus machines were open faced, with spiral bands that fanned out from the nucleus to a curved steel band that encircled the pulley. Later, the steel cams were replaced by cams made from aluminum, but that retained the distinct Nautilus shape, the purpose of which being to vary the resistance the trainee’s muscles were contracting against as the muscle moved through its fullest possible range of motion. The reason for this is that when you perform an exercise, the strength of your muscle varies as it moves from a position of full extension to one of full contraction. The Nautilus cam was designed to compensate for these variations in strength, automatically increasing or reducing the resistance to correspond to your muscle’s potential strength capacity. It is enabled to do this by means of changes in its radius, which results in greater or lesser leverage where needed. With barbells there is no way of varying resistance properly; therefore, you are always limited in your progress by how strong you are when in the weakest position.

In addition, with free weights, the resistance is always provided linearly (or straight up and down), whereas all movement in the human body is rotational around axis points, with the result that there are many points in conventional exercises where there is no effective resistance being placed on the muscles at all. The same is true with conventional exercise machines, which either employ round pulleys or pulleys that are completely out of phase with the actual strength curve of the muscle (you notice this on some round pulley machines; that the movement starts hard, then finishes easy – providing too much resistance in your muscle’s weakest position and too little resistance in its strongest position). Nautilus, however, provides correct resistance in every position: lower in your weaker positions, higher in your stronger positions, and maximum in your strongest position. According to Dr. Ellington Darden, the former Director of Research for Nautilus Sports/Medical Industries:

The Nautilus cam is the only practical method of changing the available resistance during the actual movement. It does so by producing changes in the effective lever, made possible by varying the radius of the cam. The shape of the cam is determined by careful calculation of the available strength of the involved muscle in each of the positions required by a particular exercise. In other words, physics and muscle physiology dictate the design of every Nautilus cam, which is why each machine has a different shaped cam. In a Nautilus machine, the selected weight can be as much or as little as you require, and the weight remains constant during the exercise. But the shape of the Nautilus cam varies the effective lever as movement occurs, thus increasing or reducing the effective resistance. The resistance must be in correct proportion to the potential strength in every position for the muscle being exercised.