Mind the gap
Mind the Gap!
Your force plate and your GPS are doing their job. The problem is the job you've given them.
A female field sport athlete, rehabbing a left knee. Isometric sprinter squat on a force plate.
The injured left leg was perfect. Clean application of force. Cleared to move on.
The right leg produced the same force. Same number. Symmetrical on the report...
But it was not the same movement. On the right she created a contralateral pelvic elevation (the non-stance side of her pelvis hitched excessively high in the frontal plane), with her stance knee collapsing into valgus. Her history explained it. An old right ankle injury. The ability to systemically develop force on the right was compromised from the ground up (I often see the same pattern in old ankle injuries when the athlete is running).
The knee we were rehabilitating was fine. The limb we weren't looking at was the problem.
Both limbs showed the same force capacity. Only one of them looked correct in its method. If I had not watched that test, if a staff member had run it and sent me the numbers, I would have missed it completely.
The number said symmetry. The movement said otherwise.
Two technologies, one decade
If you have worked in sports performance over the last decade, as an S&C coach, a physio, a rehab practitioner, your world has been shaped by two bodies of technology.
In the gym and the clinic: dual force plates and isometric dynamometry. On the field: GPS.
Both are excellent. Both do exactly what they were designed to do. I have no problem with either of them.
The problem is that we have asked them to answer a gap in our knowledge they were not designed for.
The Gap Problem
The Gap Problem is what happens when a tool built to measure what an athlete can do gets used to explain how the athlete does it.
A force plate tells you force capacity. An isometric dynamometer or load cell tells you force capacity. GPS tells you how far an athlete moved, how fast, and in which direction. None of them tells you HOW that athlete moves.
That does not stop people asking them to. A practitioner once said this to me directly, after a hamstring injury:
"We're going to get this athlete so strong on eccentric hamstring. We don't need to understand running. We just need to get them strong."
That athlete went on to have five hamstring injuries.
Strength was not his problem. His muscle capacity was very good. What let him down was his running mechanics and how he applied force to the ground. The answer to his issue: learn how to apply force in running, and practice it. He didn't need to be a pretty sprinter. He needed to be a football player who could accelerate and run at speed, repeatedly.
Strategy over output
Nick van der Horst (Sports Physiotherapist, PSV Eindhoven) has just put this into words. His paper, shared on social media ahead of press, is titled simply: Strategy over Output.2 Its argument is that how an athlete moves matters as much as what they achieve in return-to-play decisions. Three points sit at the center of it:
- Output measures establish what the athlete achieves: jump height, hop distance, peak force, sprint time, limb symmetry.
- Movement strategy measures establish how the athlete produces that output: joint contribution, force distribution, loading strategies, timing, compensated rhythm.
- An athlete can therefore recover the output while still producing it through a substantially altered strategy, making output restoration alone an incomplete basis for rehabilitation progress or return-to-play clearance.
I agree with every word. That squat is his third point, in the flesh. The output came back. The strategy did not.
A changed gait is not neutral
This matters most in two groups. Athletes with a highly acute injury. And athletes with any injury that changes their gait.
Limping for fourteen days. A spell in a boot. Worse still, major surgery. Every one of those changes how the athlete moves, and the brain adapts to it.
This is not speculation. After ACL injury, the brain reorganizes how it controls the knee.1 If a ligament injury can rewrite motor control, do not assume a fortnight in a boot leaves it untouched.
Getting capacity back tells you the engine is there. It does not tell you how the athlete is driving it.
Use the right tool for the Gap!
What I see too often is practitioners fitting questions to the equipment they have. Or worse, finding a number and attributing a solution to it.
Force plates and GPS answer exactly what they were built to answer. What the athlete can do. How the athlete moves, and how they apply the capacity a force plate shows you, has to be measured differently.
That is where SpeedSig sits. It is not the be-all and end-all. It does not replace your force plate or your GPS...it's not meant to. It answers the question they were never built to answer.
SpeedSig tells you how the athlete moves.
Watch the test first.
Read the number second.
Ask how, not just how much.
Stop fitting questions to the equipment you have.
Find equipment that answers the questions you have.
See What Your Hardware Already Knows
SpeedSig extracts five validated variables from Catapult and STATSports devices you already own.
Book a Demo1. Grooms, D. R., Appelbaum, G., & Onate, J. A. (2015). Neuroplasticity following anterior cruciate ligament injury: A framework for visual-motor training approaches in rehabilitation. Journal of Orthopaedic & Sports Physical Therapy, 45(5), 381–393. https://doi.org/10.2519/jospt.2015.5549
2. van der Horst, N. Strategy over Output. Ahead of press. Shared via Instagram: https://www.instagram.com/p/Dda127dDE-V/
