Strength testing, isokinetic dynamometry, force plates, and hop testing make up the standard objective return-to-sport battery after ACL reconstruction. They measure mechanical output well: force, torque, jump height, and limb symmetry. The problem is that ACL reinjury rates have stayed high even for athletes who clear that battery. This article walks through what the peer-reviewed evidence says the battery measures, what it does not, and the dimension of readiness it cannot see. The point is not that these tools are bad. The point is that they have a blind spot, and the evidence shows where it is.
What does the standard objective battery measure?
The standard objective battery measures mechanical output. Force plates capture ground reaction force, jump height, and load distribution. Isokinetic dynamometry measures peak torque through a controlled range. Hand-held dynamometry and other strength testing capture force production. Hop tests record distance and limb symmetry.
These tools share a common testing condition. The athlete performs a pre-planned movement, one task at a time, with full attention on the task. Jump on the plate. Push against the dynamometer. Hop and land on the line. The athlete knows what is coming and can focus completely on doing it well.
This is legitimate, useful measurement. A clinician needs to know whether the surgical limb can produce force and absorb load. Strength testing and force-plate testing answer that question with objective numbers, which is far better than guessing. None of what follows argues against using these tools.
The argument is narrower. The standard battery measures mechanical output during pre-planned, single-task, full-attention movement. Sport does not happen that way. The athlete reacts to an opponent, makes decisions under time pressure, and moves while attention is split. The battery does not test under those conditions, so it cannot report on how the athlete performs in them.
Why does reinjury stay high after clearance?
ACL reinjury rates are high, and they stay high even for athletes who pass return-to-sport testing. Four peer-reviewed findings make this clear.
Wiggins et al. · 2016
Meta-analysis of 19 studies on second ACL injury risk.
Roughly 23% of athletes under age 25 who return to sport suffer a second ACL injury. Almost one in four young athletes who go back is injured again.
Paterno et al. · 2014
Prospective cohort tracking athletes after return to sport.
29.5% of athletes were reinjured within 24 months of returning to sport. The two-year window after clearance is a high-risk period, not a safe one.
Losciale et al. · 2019
Pooled data on athletes who passed return-to-sport criteria.
14.4% of athletes who passed return-to-sport criteria still suffered a second ACL injury. There was no reliable protective link between passing the criteria and avoiding reinjury.
Webster and Hewett · 2019
Meta-analysis of return-to-sport test batteries and reinjury risk.
The evidence that return-to-sport test batteries reduce reinjury was called "equivocal." Passing the battery has not been shown to dependably lower second-injury risk.
Read those four findings together. Athletes who pass the standard battery are still being reinjured at rates that have not improved in step with how much objective testing has grown. The test clears the athlete, and the athlete gets hurt again anyway. That pattern points to something the test is not catching.
Why does symmetry-based clearance overestimate recovery?
Much of the standard battery is scored as symmetry: the surgical limb compared to the uninjured limb, often with a 90% pass threshold. That comparison has a hidden flaw. The uninjured limb does not stay at full strength after the injury. It weakens too. So the target the surgical limb is measured against drops, and the symmetry score looks better than the recovery actually is.
Wellsandt et al. · 2017
Limb Symmetry Index compared against pre-injury baseline.
57% of patients cleared the standard 90% symmetry threshold. When measured against their own pre-injury capacity instead of the weakened other limb, only 29% had actually recovered. The Limb Symmetry Index overestimated recovery because the uninjured limb had also weakened. The study's own reported result: "57.1% cleared 90% LSI; only 28.6% met 90% estimated pre-injury capacity (EPIC)."
Hop-distance symmetry has a second problem. The athlete can pass it without the knee itself having recovered.
Kotsifaki et al. · 2020, 2022
Joint-level analysis of how athletes achieve hop-test symmetry.
Hop-distance symmetry can be passed by compensating around the knee, shifting load to the hip and ankle. A passed hop test confirms the athlete covered the distance. It does not confirm the knee did the work.
A symmetry score of 90% or better can mean two athletes are recovered. It can also mean the other limb dropped to meet the surgical limb, or the hip and ankle quietly carried the load. The number passes either way. That is why symmetry alone overestimates how ready an athlete is.
Do force and jump scores separate the athletes who reinjure?
If force and jump testing predicted reinjury, the athletes who scored worse would reinjure more often. Two large studies tested that and did not find it.
King et al. · 2021
Study of 1,045 athletes after ACL reconstruction.
Strength and jump-performance scores did not differentiate the athletes who went on to reinjure from those who did not. The scores that clear an athlete did not separate the two groups.
Fältström et al. · 2023
Hop-test performance and reinjury in female footballers.
Better hop-test scores were associated with more reinjury, not less. The relationship ran in the opposite direction from what the test is used to assume.
There is a further point worth stating plainly. Force-plate-based return-to-sport testing has very little second-injury outcome validation in the literature. The studies that follow athletes forward to see whether force-plate clearance predicts who stays healthy are largely missing. The tools measure force well. Whether that force data predicts a second injury is a separate question, and the evidence to answer it is thin.
Is ACL injury also a neurological event?
An ACL tear is treated as a structural injury, and it is. It is also a neurological event. The brain changes after an ACL injury, and those changes show up on imaging.
Kapreli et al. · 2009 · Grooms et al. · 2017
Neuroimaging of motor control after ACL injury.
After ACL injury, the brain reorganizes and shifts toward a more vision-dependent strategy to control the knee. The athlete starts relying more on what the eyes see and less on the joint's own sense of position. Grooms et al. (2017) corroborated the same visual-motor reorganization.
The neurological side is not only a consequence of injury. It can come first.
Swanik et al. · 2007
Neurocognitive testing before ACL injury.
Slower reaction time and slower neurocognitive processing measurably preceded ACL injury. This is a pre-injury risk factor, not only a post-injury finding.
Rice and McNair · 2010
Quadriceps weakness after knee injury.
Quadriceps weakness after knee injury is partly a neural activation failure, called arthrogenic muscle inhibition. The muscle is not only smaller. The nervous system is not driving it fully.
There is one more piece of logic that the standard battery cannot answer. Paterno et al. (2014) found that roughly two thirds of second ACL injuries landed in the knee that was never operated on, the contralateral side. A limb-specific strength or force test only measures the limb it tests. It cannot explain an injury in a limb it never assessed. If a meaningful share of second injuries lands in the knee that was never operated on, the risk cannot live only in the surgical limb. It lives in the athlete's nervous system, the system that controls both legs.
What does this mean for the return-to-sport decision?
The standard objective battery is necessary but not sufficient. A clinician still needs to know the surgical limb can produce force and absorb load, and force plates, dynamometry, and hop tests answer that. The evidence above does not say to stop using them. It says they do not measure everything that matters.
The dimension the battery does not measure is cognitive-motor and neurological readiness. That includes reaction time, decision-making under load, dual-task control, and the visual-motor strategy the brain adopts after injury. These are the demands sport places on an athlete, and they are the demands the evidence keeps pointing back to.
Cognitive-motor reactive training systems, including QuickBoard, are built to assess and train the neurological readiness dimension that force and strength testing does not capture. Where force plates measure mechanical output during pre-planned movement, cognitive-motor reactive testing adds a visual stimulus and decision demand, so the clinician can see how the athlete performs when attention is split and the movement is not rehearsed. It answers a different question, alongside the force and strength battery, not instead of it.
For the clinical vertical detail, see Ortho Rehab and Athletic Training. For the peer-reviewed studies, see the published Research library.
How does this change Monday morning?
The practical move is to add cognitive-motor assessment to the return-to-sport workflow already in place, not to swap anything out. The strength and force battery stays. The cognitive-motor piece sits next to it.
In a typical sequence, a clinician runs the strength and jump testing the way they always have. Then, in the same return-to-sport visit, they add a reactive task that introduces a visual stimulus and a decision under time pressure. The athlete reacts to a cue rather than performing a movement they already memorized. The clinician compares the affected and unaffected side under that cognitive load.
The value is in the comparison. An athlete who looks symmetric on hop distance can still show a slower or less symmetric response once a decision is added. That gap is the cognitive-motor readiness the force battery did not surface. It becomes one more input the clinician weighs, alongside strength data, hop symmetry, time from surgery, and clinical judgment.
None of this replaces the clinician's decision. It gives that decision one more category of objective data, drawn from the kind of demand the athlete will actually face on the field.
What does the evidence not say?
This article is built on peer-reviewed studies, and being precise about their limits is part of using them honestly. Three caveats matter.
First, the reinjury studies cited here did not classify whether the second injuries were contact or noncontact. The reinjury rates are reinjury rates, full stop. Nothing in this article should be read to mean those second injuries were all noncontact, or that they were all preventable by training.
Second, there is no QuickBoard-specific study showing that QuickBoard prevents or reduces ACL reinjury, and QuickBoard does not claim one. The claim in this article is category-level only: cognitive-motor reactive training addresses a readiness dimension that force, strength, and jump testing do not measure. That is a statement about a measurement gap. It is not a promise of fewer second injuries.
Third, the gap in outcome validation cuts both ways. Force-plate return-to-sport testing has little second-injury outcome validation in the literature, and cognitive-motor testing has not been validated against second-injury outcomes either. The honest position is that the standard battery has a documented blind spot, and cognitive-motor readiness is a reasoned, evidence-informed candidate for part of what falls in it. It is not a proven fix.
Takeaways
- Reinjury stays high after athletes pass the standard battery: 14.4% of those who passed return-to-sport criteria still suffered a second ACL injury (Losciale et al., 2019), and test batteries have not been shown to dependably lower that risk (Webster and Hewett, 2019).
- Symmetry-based clearance overestimates recovery, because the uninjured limb also weakens: 57% cleared the 90% threshold but only 29% had actually recovered against their own baseline (Wellsandt et al., 2017).
- The battery measures mechanical output during pre-planned movement; it does not measure the cognitive-motor and neurological readiness sport actually demands. Add a reactive, decision-loaded assessment alongside the force and strength battery, not instead of it.
Common questions on force-plate testing and ACL return-to-sport
Do force plates work for ACL return-to-sport testing?
Yes, for what they measure. Force plates measure ground reaction force, jump height, and limb symmetry accurately during pre-planned movements, and that data is useful. The documented blind spot is that force-plate return-to-sport testing has little second-injury outcome validation, and force and jump scores have not separated the athletes who go on to reinjure from those who do not (King et al., 2021). Use force plates for mechanical output, and pair them with assessment of cognitive-motor readiness.
Why do athletes reinjure after passing return-to-sport testing?
Reinjury rates stay high even after clearance. Losciale et al. (2019) found that 14.4% of athletes who passed return-to-sport criteria still suffered a second ACL injury, with no reliable protective link between passing the criteria and avoiding reinjury. The evidence that test batteries reduce reinjury is equivocal (Webster and Hewett, 2019). One reason is that the standard battery measures mechanical output but not the neurological and cognitive-motor readiness dimension.
What is the Limb Symmetry Index and why can it overestimate recovery?
The Limb Symmetry Index compares the surgical limb to the uninjured limb, and a common pass threshold is 90%. It can overestimate recovery because the uninjured limb also weakens after injury, so the comparison target drops. Wellsandt et al. (2017) found that 57% of patients cleared the 90% symmetry threshold, but only 29% had actually recovered when measured against their own pre-injury baseline.
What is cognitive-motor or neurological readiness?
Cognitive-motor or neurological readiness is the brain side of recovery: reaction time, decision-making under load, dual-task control, and the visual-motor strategy the brain adopts after injury. Neuroimaging shows the brain reorganizes after ACL injury and shifts toward a more vision-dependent strategy to control the knee (Kapreli et al., 2009; Grooms et al., 2017). Force, strength, and jump testing measure mechanical output and do not capture this dimension.
Does QuickBoard reduce ACL reinjury?
No QuickBoard-specific study supports a reinjury-reduction claim, and QuickBoard does not make one. QuickBoard is a cognitive-motor reactive training system built to assess and train the neurological readiness dimension that force and strength testing does not capture. The claim is about a measurement gap, not a guaranteed reduction in second injuries.
Citations
- Wiggins 2016
- Paterno 2014
- Losciale 2019
- Webster 2019
- Wellsandt 2017
- Kotsifaki 2020
- Kotsifaki 2022
- King 2021
- Faltstrom 2023
- Kapreli 2009
- Grooms 2017
- Swanik 2007
- Rice 2010
See QuickBoard research for full citation details.