The (real) 411 on TRX
Fake (fitness) News…
Gregory Gordon, MA
In our last installment, we looked at some of the current fitness marketing “news” against the use of exercise machines i.e., the type that has a weight stack that you typically sit in and stick a pin into. As we covered in our last issue, most of the typical bias centers around a central theme; exercise machines often have a guided or fixed path of movement, often isolate a single joint, and you are often seated while performing these movements. Other exercises such as squats or cleans or bodyweight exercises such as pull ups and push ups require the use of multiple joints and are performed without the use of a guided path or seat, thereby making it more functional=transferrable to “real life”. Are these claims true? To summarize from our last issue, NO, they are not. ANYTHING that helps you produce force is a functional exercise, including exercise machines. With that premise as our basis, it then stands to reason that exercises which limit your ability to produce force could actually be considered (context-dependent) less functional. So, in that spirit, let’s explore the hypothesis that TRX and other bodyweight training methods are superior to exercise machines to see if that is real or fake (fitness) news... The TRX Band If you have been in a gym in the last decade you almost assuredly have seen a TRX band. They are a heavy duty nylon straps that suspend from an attachment, allowing the straps to become a lever in which you can perform exercises on. Typically people use their own bodyweight as resistance and perform a myriad of pulling, pushing and lower body exercises on the straps. They were “invented” (people have been using ropes and chains for various exercises for decades before TRX) by a Navy Seal, so, the marketing behind the product, and it’s relative ease of use and set up has helped drive it’s immense popularity.
As we showed in our last newsletter, even gyms who invest thousands of dollars in equipment often blatantly critique the use of that equipment in favor of doing bodyweight exercises on apparatus such as a TRX, under the construct that bodyweight exercises are more functional. We already demonstrated that producing force is the single biggest determinant in the functionality of an exercise, so, let’s take an objective look at how the TRX band stacks up with other forms of exercise.
This performer is doing a push up on a TRX. One of the difficulties you might have noticed with using the TRX vs a machine is, how much weight am I moving? With a machine, even with respect to various cam and pulley configurations, there is a number on the weight stack that gives you a representative value. A thoughtful exerciser will look at these values over a period of time to get some indication of progress. With a TRX band, you guessed it, there is nothing to help you determine how much you are moving. Think it’s your entire body weight? Nope. Also, sometimes it might feel much easier than other times…why would that be? Well, the difficulty is going to be largely based on your body position relative to the strap. So, for the thoughtful exerciser, who enjoys using the TRX, wouldn’t it be great to know much load they are actually pushing? To figure this out we need to use a little bit of math…
This is my client JJ who is approximately 6’ tall and weighs 185 lbs So, how do we go about figuring out how much force he would have to come up with to do a push up in this orientation? The equation would look like this:
(force of body weight)x(distance of body weight)=(ForceTRX)x(DistanceTRX)
For the first position, JJ is in a very common TRX type push up alignment, and when we measured distances, this is what the equation looks like:
61.6 or 62 lbs
So, essentially JJ is pressing a third of his bodyweight here, which comes out as 62 lbs or approximately 31 lbs on each side. There is nothing wrong with this per se, but, this is well below the load we use when bench pressing or using dumbells for a chest press type exercise.
Well, just lower down into a “real” push up position you say...Sure, let’s take a look at that. When the body is basically parallel to the ground, the COM & TRX move a little bit further from the the axis of rotation for the entire body which changes our equation:
555ft lbs% 4.5
123lbs or 66% of body weight
So, essentially in this alignment, JJ is pressing 123 lbs or about 66% of his bodyweight. This is certainly a good amount of load. However, if I wanted to induce the overload principle; an amount of load previously unaccustomed to, this would not be an adequate amount to provoke a significant stimulus as JJ routinely bench presses significantly more (70-100% of his body weight on bench press). Could I load a TRX push up in the same way? Possibly, but I would have to wrap clients in extremely heavy weighted vests or put weight plates on their back, or figure out some other way to add external load which definitely takes away from the convenience of the TRX, one of the major selling points of the product.
Another thing to consider is that the construction of a TRX, which mimics a bench press in some ways through each arm having some influence of output on the other side, is less stable than a barbell or flat ground. The tension put into the straps by the bodyweight of the perfomer creates some rigidity, but, not a great deal. A machine on the other hand, where the path may be fixed offers a lot more stability. Why is this important? The more unstable the condition, the more the body will co-contract muscle around a joint in order to increase joint stiffness (Behm et al., 2012). Think about walking on ice in sneakers, do you move around in a flowing and graceful way, or do you take shorter steps and limit your range of stepping motion? Right, we shorten our strides while taking shorter steps to enhance stability in an unstable environment.
The instability offered by the TRX creates significantly more co-contraction of both agonists and antagonists (muscles that either move the joint in the intended direction or oppose it) then you would most likely see in a barbell press. The extreme end of co-contraction is an isometric contraction where there is no movement of a joint at all, just muscular tension. Is increasing co-contraction a pro or con? Neither! Increasing co-contraction around a joint can be a very useful exercise, when the goal is enhancing stability, or limited motion.
If the goal is enhancing movement however, particularly movement at a high velocity, increasing co-contraction can be detrimental. Part of skill acquisition is the pruning away of any muscular contraction not necessary to accomplish the task. Actually as one increases dexterity at a task there is often LESS overall muscular activation, as too much co-contraction creates a quasi-isometric like condition that leads to increased joint stiffness, slower movement and metabolic inefficiency.
So, bottom line, while the TRX can be a quick, convenient tool to use, it’s application would be for developing increased co-contraction and stability. As you are limited to around 65-70% of your bodyweight without an external devices, it’s application for building maximal strength is limited, and as a tool for developing power it is extremely limited. Therefore, is it real or fake news that the TRX is superior to other modalities of training for building strength, power and endurance? FAKE NEWS!!!
(Behm, D et al.,) Int J Sports Phys Ther. 2012 Apr; 7(2): 226–241. THE EFFECTIVENESS OF RESISTANCE TRAINING USING UNSTABLE SURFACES AND DEVICES FOR REHABILITATION