Purpose of Cams on Selectorized Weight Stack Strength Machines

By: Brian Lewallen   On: Wednesday 10 November, 2021

Cams address the fact that each muscle group has a separate strength curve that must be challenged for optimal results. To reach these results in building muscle strength and flexibility, the weight resistance on a machine must match the strength of the user’s specific muscle group.

With only a series of pulleys and cables and no cams on a machine, the weight resistance would not mimic the muscle group being used and the machine would not deliver the best outcome.

Leg Extension strength curves throughout the full motion. 

80-85% in the beginning

100% at mid-range

80% at the end of the motion

For example, a leg extension primarily targets thigh or quad muscles. When starting a repetition, the user’s strength is about 80-85% of their full-strength capability, when the lower leg is in about the 90-degree position versus the thigh position while seated. But as the leg extension motion continues, 100% strength is reached by the midpoint of the leg extension movement, but then tapers off in the last 20% of the motion to back to about 80% or less of the user’s strength.

To challenge and develop the muscles completely, the weight stack’s resistance must be modified to mirror the strength curve of the individual’s particular muscle group.

How Does a Cam Do This?

The cam has an eccentric shape, meaning it’s not a round circle. The radius of the cam from the center axis of the cam changes as the cam rotates with the cable connected to the weight stack. The larger the radius, the greater the distance the weight stack moves. This motion creates what is called in physics, work!

With less weight stack motion, less weight resistance is being created. So, if the cam shape is varied to match the user’s muscle strength, the resistance should feel almost even throughout the repetition and maximum results are achieved in activating the specific muscle groups.

Do All Muscle Groups Share the Same Resistance Curves?

No. For example, while doing any kind of upper body pressing motion,  like bench presses, shoulder presses, incline presses, and leg presses, the muscles used for the pressing action actually get stronger throughout the range of motion and peak at the very end of the exercise.

Pressing motion using the Bench Press

As a result, the radius of the cam gets progressively larger as the pressing action is executed. This is vastly different from the cam of a leg extension. Some call this a “progressive” cam as opposed to the cam of a leg extension that is referred to as a “regressive/progressive/regressive” cam.

Every single selectorized strength machine must be engineered to yield maximum results to the users and they are not all the same. Some 50 years of research and development have contributed to the shape and function of the Muscle D Fitness selectorized machines and there are no compromises.

Leg Press machine has the same increasing strength curve as all the other Pressing machines.

Contact Us to find out more about Muscle D Fitness selectorized machines.