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Fused Versus Independent Movement Arms

Exercise equipment is typically engineered to either have fused or independent movement arms. Just to clarify, the movement arm is what the exercise subject pushes or pulls in order to perform each exercise, as most movements fall into one of those two categories. With independent movement arms, both limbs are operating separately lifting and lowering the resistance provided by the weight stack. A fused movement arm allows both limbs to work together to move the resistance and perform the muscular function targeted in the exercise. Both fused and independent movement arm-based machines can be used effectively in a comprehensive strength training program, provided there is properly regulated frequency, intensity, and volume, and that sleep and nutritional requirements are met.

There are many inherent problems with using independent movement arms. Even in exercise subjects who are not injured, there is often a strength discrepancy between one's dominant and non-dominant limbs, and this can complicate matters. In addition, from a motor learning standpoint it is far more difficult to control two movement arms than it is to control one, which usually means there will be a significant loss of focus on the targeted musculature. This will also result in a lack of trunk and/or neck stability, which makes it extremely difficult to achieve a meaningful muscular inroad. Accompanying these challenges is the danger of unilateral loading of the pelvis and spine. This happens when an exercise subject works only one side of the body at a time and should be avoided whenever possible, particularly when entering or exiting a piece of equipment. Safety must be priority number one. Dumbbells are another example of independent movement arms, and I try to avoid using them whenever possible. Inevitably, most clients have a difficult time controlling them safely and navigating proper speed and turnaround technique, but I do occasionally use them for the Bicep Curl exercise if elbow or wrist problems prevent the use of a barbell.

Most of the commercially available equipment brands manufacture machines with independent movement arms, even Nautilus and Hammer Strength, whom I hold in higher esteem than most. Many years ago at a commercial gym where I worked, I used a Hammer Strength Leg Press that had independent movement arms, and I could not understand why I lifted significantly less weight on that machine than on a similar machine that had a fused movement arm. This was well before I knew anything about motor learning. The movement I produced was choppy and awkward, and I had to think far more about controlling the movement arms when I should have been focused on fatiguing my glutes, quadriceps, and hamstrings. A few years later when I worked at Fairfax Racquet Club, there was a MedX Pulldown machine that had independent movement arms. It was a great piece of equipment that had articulating handles, but it was difficult to focus on getting a proper inroad when pulling two different movement arms. I solved this problem by placing a straight bar attachment across the handles, thus rendering it a fused movement arm.

There is a hierarchy of learning difficulty in exercise that Ken Hutchins discusses in the book "Super Slow: The Ultimate Exercise Protocol." Independent movements fall into the more difficult to learn category, along with blind movements (where movement takes place behind you), alternating movements (such as doing a Bicep Curl one arm at a time), and simple movements (rotating around a single joint). Exercises like Hip Abduction and Adduction (which we perform at Total Results, but only as a Timed Static Contraction) may seem like independent movements when utilizing a machine since they involve the legs moving away and together, but are in fact contracting against a fused movement arm. Safe and productive exercise should be an intellectual endeavor, but should not be overly complicated by having to move one limb at a time or two limbs in different directions at the same time. There are only two exercises that I can think of that must be performed unilaterally. One is Torso Rotation (MedX manufactures an excellent machine), but I believe it is a largely unnecessary exercise for most people. The other is External Rotation for the rotator cuff muscles of the shoulder. To my knowledge, the only way this can be done is unilaterally, and we perform it as a Timed Static Contraction.

All of the machines at Total Results have fused movement arms. Our exercise protocol is already challenging enough without needlessly complicating things by using independent movement arms. An exercise like the Leg Press already has a bit of inherent danger to it, in that most people have one leg slightly shorter than the other. The shorter leg can lock first, twist the pelvis, and injure the lower back, so it is very important for the instructor to properly set the machine's end point in order to avoid this scenario. When rehabilitating clients following surgery, we occasionally perform unilateral movements in the very earliest stages, but most of our clients have gotten strong enough prior to surgery that this is not necessary. Whatever discrepancy there is in strength between the affected and non-affected limbs will usually even out over time as both limbs get stronger by pushing or pulling against a fused movement arm. In addition to all of that, using a fused movement arm is simply more efficient for achieving a proper exercise stimulus in minimum time without consuming too many recovery resources along the way. It takes far less time to train both sides of the body at once.

Don't be fooled by typical fitness industry misinformation and terms like "muscle confusion" or the need to "shock the body" in order to produce results. If all you have at your disposal is dumbbells or machines with independent movement arms, do your best to move slowly and carefully, but it will be much more difficult from a motor learning perspective. People have gotten stronger in this fashion, but there is a better way. This is why the machines at Total Results are so valuable in enhancing safety as well as the overall exercise stimulus. Experience the difference today.

Posted February 09, 2023 by Matthew Romans