Exercise Analysis - Single Cable Machine
Working against opposition transmitted through a cable/pulley system is a great way to stimulate your muscles because cables offer a variety of advantages over free weights. For example, by making subtle changes of the position of the involved joint in relation to the pulley, you can dramatically alter the loading pattern that the weight you have selected provides. This is not possible with free weights where the line of pull of the opposition is always directed straight down (gravity). And cables also score big over machines because they accommodate any limb length or range of motion that a user can present.
Last month, I described exercises that can be performed on a cable crossover machine. In each of these cases, the maneuver required opposition that was directed away from the side of the body, so standing perpendicular to the weight stacks in the center of the machine was the requisite body position. This is an effective use of cables, but there are also many other exercises you can do while facing the pulleys, so single cable stations also provide useful training tools.
Much like cable crossover machines, single cable stations generally have both a high and low pulley. Alternatively, some have a single pulley that can be adjusted. This version is ideal because it gives you the opportunity to present a wide range of loading angles to your muscles. For example, you can position the pulley at the lowest point to perform maneuvers that involve pulling a weight up and at the highest for ones where you pull a weight down. In addition, you can secure it anywhere in between and, importantly, at the level of the rotating appendage to target muscles that initiate movement in the horizontal plane (the rotator cuff muscles of the shoulder, for example).
To exemplify why the cable load is far more accommodating than even the most user-friendly resistance training machine, consider using a single cable to perform an exercise that is typically not considered a cable movement. Usually, one-arm overhead extensions are done with a dumbbell: The exerciser lowers a weight behind their head by bending their elbow and then extends back up to work their triceps. But the loading pattern provided by the weight in this case is far from ideal. Unfortunately, the position of the upper arm dictates that as full elbow extension is approached, the load will progressively decrease because the moment arm of the opposing load (the perpendicular distance between the line of pull of the force and the joint at which movement occurs) is reduced. In fact, when end-range is reached and the arm is extended straight over head, the load is effectively zero and there is virtually no opposition to elbow extension at this critical stage for muscle stimulation.
Savvy exercisers might suggest that the inappropriate loading pattern on overhead dumbbell extensions can be remedied by simply altering arm position by 90 degrees. For example, triceps kickbacks performed with the upper arm parallel instead of perpendicular to the ground involve maximal load at end-range extension. However, this is not necessarily an optimal solution. The elbow extensors are not very capable at end-range, so encountering the greatest effective load at this point will serve to dramatically limit stimulation throughout the rest of the range of movement. In other words, in order to lock out fully with your upper arm perpendicular to the ground, you’ll have to choose a very light dumbbell which won’t provide much of a challenge throughout the rest of the range. Kickbacks are also different because the arm is not raised at the shoulder. One of the three heads of the triceps also raises the upper arm so shortening it by holding the arm above the head alters its relative contribution. Consequently, overhead extensions and kickbacks aren’t interchangeable from a muscle activation standpoint.
A single cable machine offers the perfect means for performing overhead extensions with the ideal loading pattern. To set up for this movement, simply position a flat bench perpendicular to the weight stack and hook a rope or D-handle to the cable coming from the bottom pulley. The movement involves sitting on the bench facing away from the stack with the attachment in your hand and extending your arm overhead like you would with the dumbbell. But in this case, the line of pull of the opposition is no longer a line directed straight down; instead, it is directed toward the pulley, so the perpendicular distance from the cable to your elbow establishes the moment arm through which the opposing force (the load you have selected on the stack) is applied. This means that at full extension, the opposition is still significant. In addition, you can change the loading pattern quite easily. For example, if you find the lockout is not loaded enough, you can sit further from the pulley. As long as you don’t change the angle of your upper arm at the shoulder, this will lengthen the moment arm and increase the effective load at full extension. Similarly, sitting closer to the pulley decreases it. This is also useful because you can make subtle adjustments from rep-to-rep to vary the opposition as muscle fatigue mounts.
This article was originally published in New Living Magazine, which can be accessed on-line at www.newliving.com.
