ARX vs. The Isometric Machines
// BY JIM KEEN
“So How Is ARX Different?”
One of the common questions we get centers around the ways in which our technology is different from a type of exercise machine that performs isometric contractions.
“Isometric” in this context refers to a mechanism that permits muscular contraction against resistance as the length of the muscle remains the same. That is, there is no movement during the exertion. No concentric contraction (active muscle shortening) and no eccentric contraction (active muscle lengthening).
This is in contrast to normal weight lifting, where you lift and lower a weight using concentric and eccentric contractions.
The claims surrounding isometric machines are compelling, but there are limits to the applicability of this type of technology. In this quick article we’ll review the good, the bad, and how ARX fits into the picture.
Isometric Machines: The Good
This one is the most obvious. Isometric contractions are the safest-possible way for a person to administer mechanical loading to the body for the purpose of resistance exercise.
Even very slow-movement weight lifting is ever so slightly more risky than non-moving contractions on an isometric machine.
The elderly, the rehabilitating, and the inexperienced can all get many of the benefits of strength training merely by adopting a consistent routine of isometric exercise.
While ARX boasts granular quantification of dynamic, moving muscle contractions, the next best thing is to quantify a non-moving contraction. As far as I am aware, all of the commercially-available isometric machines have readouts that display the user’s performance and record their data.
Data collection is highly desirable, and it is not very hard to quantify your performance when you’re performing isometric exercise.
The best thing that isometric machines have going for them is their ability to enhance bone density. We know that high—but not moderate or low—levels of mechanical loading are required for the accrual of new bone tissue.
This study, as another example, showed that isometric contractions can increase bone density by 14% in one year of 1x/week sessions.
Along with bone density enhancement, isometric machines carry with them all the benefits that can be had through the application of mechanical loading on the muscles. Primary among these is strength improvement.
Any muscle/joint system that is exposed to meaningful mechanical loading—like the type that is possible using isometric machines—will produce an increase in contractile strength as an adaptive response. This is a huge benefit of resistance exercise, and one that is produced—to a certain degree—by isometric contractions.
Resistance training is known to cause improvements in glucose utilization, insulin sensitivity, and endothelial health. These are all adaptive responses to the stimulus of the muscles being made to contract against resistance.
When a set of isometric exercise is continued longer than fifteen seconds, the phosphagen energy pathway is fully exhausted and the glycolytic energy pathway becomes dominant, up until around two minutes have elapsed, at which point the oxidative energy pathway begins to contribute.
A properly-executed isometric set of exercise can fully stimulate all three of these energy pathways.
Isometric Machines: The Opportunities for Improvement
No Eccentric Contractions
The biggest drawback to the isometric machines is that they make it impossible to perform eccentric contractions. As we know, the greatest capacity for force production of any skeletal muscle exists when the active muscle is being made to lengthen against resistance.
We can control the descent of a far heavier weight than we could have lifted, in other words.
The stimuli of mechanical tension and microtrauma to the muscle fibers are only optimized with the inclusion of eccentric contractions in your resistance exercise protocol.
You can produce far more force—and thus expose your bones and connective tissues to more mechanical loading—during a safe, properly-loaded eccentric contraction than you can with an isometric contraction.
This means that, in fact, as good as isometric contractions are for stimulating improvements in bone density, properly-loaded eccentric contractions are even more effective for this purpose.
And as good as isometric contractions can be for the stimulation of strength increase, properly-loaded eccentric contractions are even more effective for this purpose.
So using a resistance exercise tool that precludes the performance of such eccentric contractions represents a huge drawback, and one that the isometric machines cannot overcome.
No Concentric Contractions
It’s not all about eccentrics though. A concentric contraction is also highly valuable, as it allows the filaments inside the muscle fibers to slide past each other. In this process, more energy is used than a comparable contraction without any movement—such as those performed on isometric machines.
This article from Dr. Brad Schoenfeld points out that:
Repetitive muscular contractions cause a compression of blood vessels, impeding both inflow and outflow during exercise and creating a hypoxic intramuscular environment. There’s evidence that the hypoxic effect mediates a hypertrophic response, conceivably by the buildup of metabolites and reduction in pH levels associated with such training.
Constant tension is an element of isometric training of course, but there is something beneficial about a series of excursions per se. That is, there are things accomplished by repetitive concentric muscle action that are not accomplished by a single isometric contraction.
ARX Wins Again
The first thing I always point out when people ask about the difference between ARX technology and the isometric machines they’ve seen advertised is the fact that ARX does isometric contractions too.
Put more bluntly, “an ARX machine becomes an isometric machine if you unplug the motor.”
Every benefit I’ve listed for isometric machines is also a benefit of ARX technology. There is no result possible through the use of isometric machines that cannot be duplicated and surpassed through the use of ARX.
This chart summarizes this nicely:
The reverse of this is not true: there are many things possible through the use of ARX that cannot be matched by any amount of work on an isometric machine.
The Bottom Line
So there you have it. Isometric machines definitely have their place, especially for those looking for the bare minimum of what’s possible through resistance exercise. For someone over fifty needing to avoid further bone loss, this is a huge deal.
You might say that a standard weight room yields a greater total effect than an isometric machine, and for most things you’d be right. But the ease of use and convenience of the isometric machines compared to the weight room makes them the more palatable option for millions of people who can’t or won’t make “the gym” a part of their lifestyle.
And half of a sure thing is better than twice of nothing.
However, all the reasons one would use an isometric machine can also be used to argue for the use of ARX machines, and then some.
ARX can do precisely the same thing that the isometric machines do, with no compromise. Just as easy to use, just as quantifiable, just as efficient, and just as much loading of the bones and muscles.
Perfectly-loaded concentric and eccentric contractions through a full range of motion give the user the benefit of adaptive resistance that responds to the user in real time. This maximizes the benefits of resistance exercise in a way that the isometric machines cannot match.
Just because ARX machines are better does not mean that isometric machines “don’t work” or that anyone should avoid them.
But if you have access to both an ARX machine and one of the isometric machines, the choice is obvious.
Welcome to the future of exercise.
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