Power · 3 min read
Dual force plates record what each limb contributes separately. A difference between them is a finding, not a fault, and treating it as a fault is the most common error made with this data.
By Chris Gkoufas, DVOTION ·
Perfect symmetry is not the normal state of a body, and it is not the target. Sport shapes the body: a side-dominant action repeated over years can produce a durable difference, and that difference may be part of how an athlete performs well rather than something obstructing it.
A measured difference tells you the limbs contributed unequally to that task on that day. On its own it does not tell you whether that matters.
Context is what makes the number interpretable.
Consistency across protocols matters: a difference that appears in every task is a different finding from one that appears in a single test. Direction matters: a difference that aligns with the athlete's sport and history is less surprising than one that does not. Change over time matters most of all — a stable difference and a widening one carry very different weight.
What is being measured matters as well. Reviews of the published work find that left-right differences in strength are the ones most often associated with reduced jumping, kicking and cycling performance, while the findings for sprinting, change of direction and balance are mixed. A difference in one quality does not carry the same weight as a difference in another.
Agreement with the movement assessment matters too. Where force data and movement findings point the same way, confidence is higher. Where they disagree, that disagreement is usually the more useful observation.
A left-right difference does not diagnose an injury and does not predict one. This is a performance assessment, not a clinical examination, and framing an asymmetry as an injury risk overstates what the measurement supports.
It also does not follow that the correct response is to train the two sides towards equality. In some cases the difference reflects a strategy that suits the athlete's sport, and reducing it would have no benefit.
A difference is a prompt to look, not a conclusion. It is read alongside the movement assessment, the athlete's training history and the demands of their sport before any training decision follows from it.
Where it does prompt a change, that change is usually in exercise selection or in how a movement is loaded, rather than in adding isolated work to one side. And it is worth re-measuring under the same protocol before concluding anything has changed.
There is no single threshold that applies across sports and tasks. What is informative is whether a difference is consistent across protocols, whether it fits the athlete, and whether it is changing.
No. A performance assessment cannot establish injury risk. If something in the assessment warrants clinical attention we will say so and recommend an appropriate professional.
Not automatically. Whether a difference is worth addressing depends on your sport, your history, and whether it is stable or changing. That judgement is part of what the assessment is for.