By John Cronin
One of our primary challenges as strength and conditioning coaches and technical coaches is that a great deal of gym-based strength increases are non-specific, and transference to speed for sporting performance is less than optimal. I maintain that it is easy to develop a better athlete—as, by definition, if you make them stronger, fitter, or more agile, you have improved athleticism. However, and more importantly, do these increases translate to being a better player, with improved on-field or on-court performance? In many circumstances, the answer is, sadly, no.
Therefore, our challenge is to find training methods that improve strength and power specific to each of our unique training and performance situations. This is called “optimizing transference,” and in terms of speed development, a new training tool that optimizes transference is wearable resistance (WR), also known as light variable resistance training (LVRT). To be honest, this new kid on the block is not in fact that new—click on Google and you can see plenty of different ideas around what wearable resistance looks like, with research dating back to the 1980s.An Exogen suit with fusiform weights lets us overload speed and constituent parts like nothing else. Click To Tweet
There are, however, a couple of new additions to this area, including the figure-hugging Exogen suits with fusiform weights (50-300 gm/1.7-10.6 oz) that you can affix to the body anywhere there is a compressive garment—i.e., vest, shorts, arm and leg sleeves (see Image 1). As such, in terms of high-velocity movement-specific strength and metabolic training, I haven’t come across anything better—and I have been in the game a long time and had my head across a lot of different ideas and technologies to improve speed. This technology has enabled us to overload speed and the constituent parts (e.g., arm mechanics, step length, step frequency, etc.) like no other tool.
Why Is Optimizing Transference Important?
Let’s take as an example the squat, since it is a foundational movement of most strength training programs. There is a lot of research out there showing that the squat transfers really well to squat-like performance; the transfer to jumping and sprint performance, however, is not that convincing. Big increases are needed in squat strength before we see small improvements in sprint performance—if any occur at all.
When you compare squatting and sprinting (see Image 2), is it any wonder there is minimal transference, given the characteristics of the exercises? We rack our brains about how we can make training more specific so the likelihood of transference of training adaptation to athletic performance is more likely. We search for those exercises that have similar posture or force vector specificity. It is important to simulate the type and duration of the contractions that the athlete produces (i.e., contraction and metabolic specificity). We know we want to train fast because we know about velocity-specific adaptation. And so on and so forth.
As I look back, I think we have overcomplicated it all to show how smart we are, and as I get older, I want to simplify things. Therefore, my advice is to slap on an Exogen suit with 200-600 gm/7-21 ounces affixed to your lower limbs and start sprint training, as your strength and metabolic training are not separate from what you do but rather part of it. And guess what? You are most likely ticking a lot of those “specificities” that optimize transference of strength gains to sprint performance.
Now, I am guessing that you are likely thinking, “How can you seriously think that moving 200 grams/7 ounces is a strength stimulus, and moreover, that it can be a strength stimulus that can improve sprinting performance?” This is when we need to take a first principles physics approach (established science and not assumptions) to understanding WR: By understanding a few biomechanical formulas, the value of WR becomes much clearer, and in turn it becomes difficult to argue with the benefits of this type of training. What we bang our heads upon all the time is the “lift heavy” mindset, and the perception of moving 200-600 grams/7-21 ounces would offer very little to no overload to the muscular system.
Those who think like that couldn’t be more wrong. By taking a first principles approach, the naysayers will hopefully see that the future of fast is light. By this I mean that moving lighter loads—but at higher velocities during sport-specific movements—is where we need to direct much of our training. I am not saying to stop lifting heavy, as heavy resistance strength training is important for many team sports, but that LVRT offers a bonafide resisted overload depending on the magnitude, placement, and orientation of load, as well as the velocity of movement.We need to train moving lighter loads, but at higher velocities during sport-specific movements. Click To Tweet
More about these key loading parameters and the physics behind them later: The only reason LVRT won’t work is because the coach or user doesn’t know how to apply it properly. So, the aim of this series is to make sure this doesn’t happen, by embedding foundational knowledge about the physics of this technology and sharing the learnings of near-on five years of using WR.
First Principles Physics
Most of us are very interested in increasing the force capability of our athletes, as we intuitively and mechanistically understand that the amount of force an athlete can produce per unit time (impulse), coupled with the correct force orientation, is a major determinant of how fast they move. Therefore, improving force capability is a focus of some of our training. The typical way we go about this is to lift moderate to heavy loads in an explosive manner.
But let’s unpack this in a first principles type of way. The formula for force is: force = mass x acceleration. Now if we look at the example given above, the formula looks like this:
That is, if we want to develop force capability in an athlete, we typically place large external loads (mass = kilograms) on a bar, which requires large internal muscular forces to overcome or lift. But guess what? When we use that approach, the subsequent movement velocities and accelerations are small/low/slow. Now this is potentially not a problem if we are combining some slow-velocity gym training with a whole lot of on-field or on-track high-velocity training. However, I don’t want to discuss the merits of this, but rather bring attention to the fact that there is another way to develop high force capability in athletes according to first principles physics, which is often not understood and/or used. What say we flip the emphasis to the formula below, where load is light (mass = grams) but movement velocities and accelerations are high?
So, mechanically speaking, there are two ways to develop force capability: the first is a more traditional resistance strength training approach, where moving heavy masses is the emphasis; the second is the premise that wearable resistance is based on, in which movement velocity is the emphasis. Attaching a light load to the thigh or calf, and moving the loads at high velocities/accelerations, is another way to develop force capability, and most likely in a movement-specific context.
Now let’s take that concept of force orientation and optimizing transference. Without getting too complex and talking about the applications of three-dimensional forces and vectors I mentioned previously, I am pretty sure most of you can see that force capability developed during running/sprinting with WR (i.e., sprint-specific strength training as part of your sprint training with micro-loading) is more likely to transfer to sprint performance than non-specific strength training in the gym. We all know that gym-based, non-specific strength serves a function; however, if you need special strength or specific strength for sprinting, I hope you have seen the light—that LVRT is an innovative and targeted training tool for movement-specific speed development.
Obviously, from the formula I note, there are two methods to overload the muscular system to produce force, by either adding mass to the bar or limb or moving that bar or limb quickly. These are two really important loading concepts to understand if you want to optimize WR overloading. First, and potentially easiest to understand, is that as soon as we add mass to a limb, force output increases as long as the associated movement velocities and accelerations don’t decrease. With WR, however, the addition of mass can get a little more complicated when you look at the loading options you have.
The same load/mass can have varying resistive overload/forces based on its placement on the body. Click To Tweet
In Image 3, you can see different examples of loading: a) central or vest loading; b) peripheral or limb loading; c) proximal medial loading; d) distal lateral loading; e) distal medial loading; and f) medial loading. Obviously, each of these configurations places a different overload on the muscles around the hip, not only in terms of medial-lateral loading, but also in terms of loading close to the hip (proximal) versus away from the hip (distal).
For example, let’s take a 400-gram/14-ounce loading on a vest, thigh, or shank. What you would feel if you had a suit and sprinted with 400 grams/14 ounces is: vest – didn’t notice it; thigh – yep noticed that; shank – that was hard. In summary, the same load/mass can have very different resistive overload/forces depending on where you place that load on the body. To understand this second concept of LVRT further, we need to jump back into first principles physics and discuss inertia.
Momentum and Torque
Inertia is the resistance of a body to change in motion, and is a function of mass. For example, we have a 90-kg (~200 pounds) collegiate volleyball player who’s about to perform a vertical jump. Theoretically, they have to produce more than 90 kg or ~900 N (90 kg x acceleration due to gravity = 9.81 m/s2) of force into the ground to get airborne. If we put a vest on them and place 10% of their body mass (9 kilograms/20 pounds) on the vest, then they would have to produce more than 99 kg or 990 N of force into the ground to get airborne.
What we have done here is increased the volleyball player’s inertia—their resistance to change in motion—as it is taking more force to produce motion. With vest loading, that is easy to understand. With lower limb loading, however, we have an additional complexity in that the thigh and shank rotate around the hip and knee, so WR provides a rotational overload.
Many people will read this and not think much of it; however, this is what makes WR pretty unique. Meaning, it provides a direct rotational overload of the muscles. Even though a 100-meter sprint is a linear activity, getting to the finish line is the product of rotation at the legs and arms, so rotationally overloading the limbs used for sprinting makes a lot of sense. It goes back to maximizing specificity to optimize transference.What makes WR pretty unique is that it provides a direct rotational overload of the muscles. Click To Tweet
So instead of inertia, rotational inertia is what we are really interested in when talking about limb-loaded WR, and it is a biggie to understand for you to overload with WR safely and effectively. The formula for rotational inertia is I = mr2, where I = rotational inertia, m = mass, and, r = distance from axis of rotation. So, let’s take the thigh as an example: We know the thigh has mass and therefore requires rotational force (torque) to move it. The larger the thigh mass, the more muscular effort required by the hip flexors and extensors.
By simply adding more WR to the thigh, we increase the rotational inertia of the thigh, which means more muscular effort or turning forces/torques are required. But let’s not forget the second part of the rotational inertia formula (r2), which indicates that where we put the mass is really important. In fact, this has more of an influence on rotational inertia (muscular effort), as any distance change is squared.
As an example, we add 400 grams/14 ounces to the thigh mid-femur as shown in Image 4a. Let’s put some numbers into this so you can see the effect of placement on rotational inertia, and therefore muscular effort/torque requirements from the hip. I have modelled the rotational inertia associated with the thigh of an 86-kilogram/190-pound lacrosse player. In Image 5, you can see the rotational inertia associated with a variety of loads when the loads are positioned mid-thigh and distal thigh.
Let’s have a look at 400-gram/14-ounce neutral loading as shown in Image 4. By shifting the same load 20 centimeters down the leg (Images 4A and 4B), we increased the rotational inertia of the lacrosse player from 4.7% to 12.1% because the load is further away from the axis of rotation (hip). We call this distal loading, and it is one of the most important loading parameters to understand with WR, because for every cm/inch you move from the axis of rotation, the distance is squared. Hence, it has a substantial effect on rotational inertia, and therefore muscular effort at the hip.
Wearable resistance micro-loads to make sprint-specific resistance training part of sprint training. Click To Tweet
An important consideration here is that we only influence the muscles at the hip if we thigh load; if we load with the calf sleeve, however, then we influence the muscles across the knee as well as the hip. Also, it is important to understand that calf loading places the load a great distance from the hip joint and, as such, there are significant muscular work requirements to move a light load so far away from the hip’s axis of rotation. As a rule of thumb, we use a 1:3 ratio in that we believe the equivalent loading at the calf is one-third of the thigh: For example, a 600-gram/21-ounce load at the thigh has about the same rotational inertia at the hip joint as a 200-gram/7-ounce load at the calf. Finally, remember the same principles apply across the arm.
The future of fast is light, as wearable resistance uses micro-loading to provide sprint-specific resistance training as part of your sprint training, not separate from it. As such, any strength gains are more likely to transfer to sprint performance than other more traditional resistance strength training methods. In this article, we provided the rationale and guiding principles around using load and placement (distance from the axis of rotation) for LVRT. In a future article, I will discuss in detail the effects of orientation and velocity of movement as methods to overload the athlete interested in improving speed.
Here, I took a first principles physics approach to show you why WR works. However, you don’t need to talk forces, torque, inertia, or rotational inertia with your athletes or clients—these concepts are for you to understand so you can use WR in a safe and effective manner. As I said earlier, WR offers a bonafide method of resistance training based on first principles physics, so it is difficult to argue its efficacy. Ultimately, the effectiveness of this technology in changing speed capability is based on your knowledge and its application.