Coaches and trainers often adopt movements that appear to have the greatest “transfer” to an athlete’s sporting discipline when designing a training program. Once they’ve deemed what they believe to be essential, they commonly scrap or disregard any movement outside of that for its relative ineffectiveness or inapplicability. Of course, we only have so much time to train, and we simply cannot do it all, but how do coaches decide what movements an athlete should do or what is most important? Is it as simple as taking what appears to work from a surface level and disregarding the rest?
Performance coaches commonly make decisions based on the assumption that if a sporting action moves through a given plane of motion, exercises replicating (or closely mimicking) the same action automatically correlate, thus reigning as superior to those that do not. Coaches then fight tooth and nail over programming elements—like whether athletes should back squat or not—saying that it doesn’t emulate a skill like sprinting and therefore is useless. In reality, however, when properly programmed and transferred into the skill of sprinting, squat lifts can most certainly enhance performance.
Most of these topics have been beaten to death over the years, and you can simply scroll through social media to find coaches throwing literature in one another’s faces to justify or assert their position. That is not the intention of this article—the goal, rather, is to inform the reader on why it is inadequate to rely on certain theories for programming, mainly the force-vector theory.
Understanding the Literature
The force-vector theory is a recurring concept that some coaches have leaned on, where movements are classified based on the direction in which force is expressed in relation to the global coordinate frame. This means that activities such as sprint acceleration would fall under the horizontal acceleration umbrella, whereas maximum velocity sprinting would reside under the vertical. Subsequently, “horizontal” or “vertical” exercises would be more specific to their respective categories.
While at first glance this may seem like a sound theory, the principle of dynamic correspondence contends otherwise, showing us that there truly is more to human kinetics than meets the eye. Sure, athletes require unique training methods depending on their sporting discipline, but we could argue that a number of universal movements assist athletes no matter what they are doing.Sure, athletes require unique training methods depending on their sporting discipline, but we could argue that a number of universal movements assist athletes no matter what they are doing. Click To Tweet
It’s easy to understand the assumption that an exercise loaded similarly to that of a particular sporting action is as simple as a 1 + 1 = 2 equation. Take the 2018 study that examined and directly compared the relationship of vertically directed exercises (loaded and unloaded vertical jumps and half squat) and horizontally directed exercises (hip thrust) to sprint performance in top-level track and field athletes.1 Testing results for speed at the 10-, 20-, 40-, 60-, 100-, and 150-meter marks indicated that horizontally directed movements (hip thrusts) were more strongly associated with the maximum acceleration phase, whereas vertical movements (loaded and unloaded vertical jumps) were more strongly associated with top-end speed phases.
Loturco et al. concluded that “the force-vector theory is thereby an emergent methodological approach, based on a solid and well-established mechanical foundation.”1 Essentially, this newfound theory would allow coaches to select exercises based on their relative direction and apply them to the specific phase of running or sport skill the individual athlete needs to improve. Boom! That’s it! All we need to do is train athletes with exercises loaded in a similar fashion to that of the plane they travel in their sport, right?
Sounds nice, but think again.
This is most certainly a broad generalization, and according to Fitzpatrick et al.2, comes as a “direct opposition to the most commonly accepted criteria of mechanical specificity used in strength and conditioning, that is, the principle of dynamic correspondence.”
While it is true that during high-speed running, ground reaction forces are predominately vertical, whereas during acceleration, there is a greater horizontal force relative the global frame, it cannot be explained by the force-vector theory. Rather, it is simply due to the athlete’s body position.2 During acceleration, the athlete must lean forward to project greater horizontal force, meaning that the ground reaction force relative to the global frame of the body is simply projected in a more horizontal fashion.
Kugler and Jahnsen4 demonstrated the same when looking at both horizontal and vertical jumping, finding that the direction of ground reaction force is relative to the athlete, and whether they travel forward or not depends on whether they lean forward. Thus, how the body and the ground reaction force are oriented at toe-off dictates where the athlete travels. This is all further proof that perhaps the development of strength, speed, and power in athletes across the board is more similar than some would like to admit.
Dynamic correspondence supports that activities like back squatting are, in fact, mechanically similar to more “horizontal” motions such as acceleration because the direction of the ground reaction force relative to the athlete is similar despite it being different in the global frame. There is a reason fundamental movement patterns (e.g., squat, hinge, lunge, press, pull, push, etc.) have been around so long in the general physical training of athletes and will continue to be—because they work in the development of foundational qualities needed across most sports.
What Matters Most
If we were to adopt the force-vector theory to guide our programming and decision-making, how would we know when a particular movement goes from being horizontal to vertical, and vice versa?
Take our acceleration and sprinting analogy—there is not an immediate change from one to the next, but rather a gradual shift in the ground reaction forces that propel the athlete forward. Even further, how does something like a hip thrust (knees flexed at 90 degrees) directly transfer to the ground reaction forces of an athlete during closed kinetic chain leg extension?2 It certainly doesn’t, and neither do any other exercises for that manner, which is why we don’t program based on the idea of “replicating” what we see. Loturco et al.1 were certainly on to something when they popularized the use of the hip thrust and similar type exercises, as these movements have been shown to have the potential for greater glute and hamstring activation versus the back squat, which may assist in more hip-dominant skills. That would be a more justified reason to select one exercise over another within a program, not that one happens to fall in line with the force-vector theory.
For this reason, we also must do our research and select an array of movements in our programming to determine what is most beneficial for our athletes, ultimately helping contribute to better athletic potential. Nick Winkelman said it best (and I paraphrase): Athletes are a lot like racecar drivers and we as coaches are a lot like mechanics. We don’t tell the athlete how to drive the car, we just help give them a better and higher performing car to drive.Perhaps the greatest error a coach can make is getting stuck in the dogmatic thought process that lures many into believing that anything in human performance is universal, says @jimmypritchard_. Click To Tweet
Perhaps the greatest error a coach can make is getting stuck in the dogmatic thought process that lures many into believing that anything in human performance is universal. The cliché “It depends” gets tossed around a lot, and rightfully so. Is a hip thrust better than a back squat for acceleration or speed development? It depends. Numerous factors play into the required development for an individual in their given sport and the forces they encounter on their body concerning the global frame.
Having a truly deep understanding of the sport in which the athlete participates, and subsequently the physiological, biomechanical, and competitive skills they must have to be successful, is no doubt the most important factor. This leads us to the realization that there are many ways to skin a cat, and in sport a multitude of ways to get to our destination. We should prioritize helping the athlete develop the ability to produce force and produce it quickly, or display greater feats of strength, power, endurance, and speed in the context of competition.
Application of Dynamic Correspondence in Exercise Selection
The force-vector theory prioritizes the direction of force relative to the global frame, while what is clearly most important is the direction of force relative to the athlete. Adopting this theory and applying it in practice is rather problematic in that it violates the basic tenets of the relationship between the way a body is oriented and the ground reaction forces that occur on it, thus creating a great deal of misunderstanding.
Obviously, we know that the more effective approach is to make decisions based on dynamic correspondence, but how does one actually do this?The force-vector theory prioritizes the direction of force relative to the global frame, while what is clearly most important is the direction of force relative to the athlete, says @jimmypritchard_. Click To Tweet
First and foremost, identify precisely what metric or performance parameter you wish to improve. Say, for example, that you know an athlete must improve their foot ground contact time while sprinting in order to get faster, and that a specific athlete is currently somewhere in the neighborhood of 85 milliseconds. Ask yourself what exercises or movements would most effectively improve this quality in order to get to a more desirable number, like 80 milliseconds? The right answer is whatever exercises increase the performance—and what certainly does not matter a bit is the direction in which they execute the movement.
By starting with the end in mind, it is easy to work backward from this end performance goal as well as decipher whether an exercise translates to performance or not. In the case of ground contact time, you may choose to incorporate an array of vertical, horizontal, and multidirectional plyometrics to improve performance.
Lastly, we must not forget that any and every action we choose to execute is in fact a supplement aimed at improving performance. It is easy to get lost in the minutiae of all the training details we encounter while working with athletes, but at the end of the day, whatever improves the athlete’s performance most is what really matters.
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1. Loturco, I., Contreras, B., Kobal, R., et al. “Vertically and horizontally directed muscle power exercises: Relationships with top-level sprint performance.” PLoS One. 2018;13:e0201475.
2. Fitzpatrick, D.A., Cimadoro, G., and Cleather, D.J. “The Magical Horizontal Force Muscle? A Preliminary Study Examining the ‘Force-Vector’ Theory.” Sports. 2019;7:30.
3. Bryanton, M.A. and Chiu, L.Z. “Hip-versus knee-dominant task categorization oversimplifies multijoint dynamics.” Strength & Conditioning Journal. 2014;36:98-99.
4. Kugler, F. and Janshen, L. “Body position determines propulsive forces in accelerated running.” Journal of Biomechanics. 2010;43:343-348.