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Why Your Box Height Doesn't Matter

At some point, the height of the box used for box jumps has become a benchmark of sorts–the layman’s way to determine jump height. While this information get’s you in the ballpark, it doesn’t really get you to your seat. The same sort of thing happens when schools measure body fat with the Body Mass Index (BMI)… when you’re only operating with some of the information, accuracy becomes expendable.

Nevermind that boxes are being used for metabolic conditioning these days. Let’s start with why the box is an inaccurate assessment of jumping ability. Just because you can jump onto something doesn’t mean you can jump as high as that thing. No doubt, you’ve seen the extreme training videos showing how explosive and powerful all these bros are.

Guys like this jump on literally anything from crazy high aerobics steps to vending machines. In fact, here are plenty of “athletes” out there that can hit the top of a 42″ box but have a sub-30″ vertical. Why is that? The problem is, A) they get running starts, or an approach, and B) they don’t actually displace their hips enough distance from the ground relative to the object to warrant that size of box.  I’ll explain.
While an approach might be a practical tool when training specifically for certain sports such as basketball or volleyball, it doesn’t display or train raw power output. There are just too many variables at play when multiple plyometric movements occur before there is any vertical transfer of maximal force. Additionally, when assessing jump height using an approach, that data can only be compared to other jump heights using that exact same protocol.

Vertec vs Just Jump.jpg
The Vertec (L) and Just Jump Pad (R) are highly valid jump tests.

Most people that jump on these really high objects just have insanely good hip mobility and strong hamstrings. They’re able to achieve hip flexion so great that as long as they can get their feet on an object, they can curl their way on up. This says nothing of their ability to displace their hips or torso from the ground without the aid of an anchor above the ground. If you jumped up to a pull-up bar 7 feet above the ground and performed a muscle-up, would you say you jumped 9 feet? Absolutely not. Furthermore, those without the requisite hip mobility find compensatory movement through excessive lumbar and thoracic flexion. Do they have ups? Maybe, but their true jump height pales in comparison to the height of the object. There’s a reason the video doesn’t show them under a Vertec or on a Just Jump pad, each considered the gold standard in vertical jump testing. The truth hurts and honesty isn’t always the most effective marketing tool.
box-jumps diagram
The extra box height doesn’t equate to greater hip displacement and isn’t worth the excessive spinal flexion or loss of GRF absorption.

What really gets lost in translation are the purposes of the box.
The box is supposed to provide a small cue to the athlete to jump higher if a little prodding is necessary, i.e. not lazily.
The box reduces the impact of ground reaction forces on the joints by shortening the distance between the height of the athlete’s jump and the landing. The overwhelming majority of injuries that occur during jump training happen during landing. This enables the athlete, novice or veteran, to extend themselves a little further without fear of injury. Additionally, absorption of GRFs is a huge boon to the prevention of noncontact ACL injuries.
Occasionally, coaches and athletes lose sight of why train with jumps in the first place. Not all sports necessarily require you to get hangtime on a regular basis. The triple extension found in explosive jumping is highly similar to sprinting acceleration strides. If athletes are jumping on boxes too high for them, it will become immediately evident by their natural instincts to tuck the knees rather than extend fully through the hips, knees, and ankles. Smaller boxes with less frequent height increases will improve safe jumping mechanics and effective force absorption while teaching explosive triple extension and quality body control.  You know a box is too high if the athlete lands below femur-parallel depth. Landing at or above femur-parallel with no recoil is a good sign that the athlete is absorbing the GRFs properly at a box height that won’t cause bloody shins as a result of a missed jump.
An example of a quality box jump landing.

A fringe purpose of the box is teaching leg recovery. While we want the athlete to learn effective triple extension, sprinting isn’t all concentric movement. Knee recovery needs to be automatic, especially during acceleration, in order to produce one powerful stride after another. Make no mistake about it: the bros in the Youtube video don’t even have this part right. Watch it again.
Sprinting occurs predominantly in the sagittal plane–hips and knees moving up/down and forward/back… flexion and extension. Being forced to externally rotate the hips and turn the toes out in a sumo stance or knee valgus only to barely “land” is not effective AND has zero transfer to sprinting recovery leg mechanics.  Conversely, if the athlete can land on the box with straight legs, the box is probably a little bit too small.
An example of a bad box jump landing.

The last problem with high boxes, particularly if you’re training alone is the increased risk of injury. Injuries on a ridiculously high box can come in two ways: violent explosion with bad mechanics or a missed jump. It’s the latter that occurs more often than not. A missed jump can mean a lot of things. Barely reaching the top of the box doesn’t allow the athlete to “land down”. It forces them to “land forward” or “scuff”, transferring their center of mass forward and leading to a fall off the other side.
Narrow boxes that prevent an athletic stance (feet hip/shoulder width) in the landing and can lead to some pretty painful albeit comical crotch landings. Another risk comes from not quite making it to the top, leading to some bruised/bloody shins (at best) and falling backwards onto your back (at worst).
Each of these risks is bad enough on their own but when box jumps are used as conditioning exercises rather than power developers, you can basically multiply the risk x3. Highly fatigued jumping leads to shorter jump heights as the rep count increases, further increasing your fatigue level as you continue to attempt the same jump height. At some point, you are too fatigued to recover from a landing mistake and any single one of the aforementioned risks becomes a possibility.
Knowing all of this begs the question: what could possibly be the purpose of jumping on an extremely high box?
One word: EGO
It’s in an athlete’s nature to be competitive and with that comes ego. While an ego can be an asset, a healthy ego can turn to arrogance quickly if mismanaged. Check your ego at the door. Be smart and use the plyo box for what it’s meant for. If egotistical satisfaction is all that’s to be gained, then it’s not worth it. If you do feel the need whip out the measuring stick, point to your vertical jump score. That’s the only number that matters in jump measurement.

Coach Runner is the Owner and Director of Sports Performance at Full-Stride Performance. Prior to founding FSP, Runner was formerly the Strength & Conditioning Coach for the Atlanta Gladiators of the East Coast Hockey League, a minor league affiliate of the NHL's Boston Bruins. Coach Runner was also the Head Strength & Conditioning Coach for the Husson University Eagles, Graduate Assistant Strength Coach at the University of Maine, and a former collegiate hockey player for Plymouth State University. He earned his Master of Science degree in Kinesiology & Exercise Science from the University of Maine and is recognized as a Certified Strength & Conditioning Specialist by the National Strength & Conditioning Association in addition to numerous other certifications.

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