Guides · ForceDecks · 8 min read
An ACL return-to-sport force plate battery: the tests and thresholds physios actually use
A practical force plate battery for ACL return-to-sport decisions — bilateral and single-leg CMJ, drop jump, IMTP — with the limb symmetry thresholds and the strategy metrics that catch what symmetry misses.
By Vikas Kashyap · Updated 25 September 2026
Force plates have become standard in ACL return-to-sport testing for one reason: they can measure the limb-to-limb comparison that hop tests approximate, and they can see how the athlete is producing the movement rather than only the outcome. This guide is the battery most performance physios settle on, with the thresholds in common use. It is not a clinical protocol; it is a testing framework to sit inside one.
The four tests
| Test | What it adds | Key outputs |
|---|---|---|
| Bilateral CMJ | Global output and, on dual plates, the limb split during a bilateral task — where compensation hides. | Jump height, RSI-mod, propulsive impulse asymmetry, braking force asymmetry, landing force asymmetry. |
| Single-leg CMJ | Each limb's capacity on its own, without the option of shifting load. | Jump height per limb, RSI-mod per limb, propulsive impulse, countermovement depth per limb. |
| Drop jump (or single-leg drop jump) | Reactive strength and landing control under a higher demand. | RSI, contact time, peak landing force asymmetry. |
| IMTP | Maximal strength, bilaterally and per limb on dual plates. | Peak force asymmetry, relative peak force, RFD in early windows. |
The thresholds in common use
- Limb symmetry index of at least 90% on the primary outputs (single-leg CMJ height, IMTP peak force) is the widely used criterion for progression to full training; some programmes require 95% for return to competition.
- Asymmetry on bilateral tasks under about 10% for propulsive impulse and peak landing force.
- Absolute values, not just symmetry: the injured limb should also approach its own pre-injury or the athlete's contralateral baseline in absolute terms, otherwise symmetry can be reached by the uninjured limb declining.
- Drop jump RSI and contact time on the injured side within the athlete's normal range for that test.
The strategy metrics that catch compensation
On each test, look beyond the primary output at how the limb produced it:
- Single-leg CMJ countermovement depth per limb — a shallower countermovement on the operated side with matched height usually means the athlete is avoiding knee flexion under load.
- Braking (eccentric) impulse and peak braking force asymmetry on the bilateral CMJ — the deceleration phase is where offloading is most visible.
- Peak landing force asymmetry on the drop jump — the highest-demand landing in the battery.
- RSI-mod per limb — efficiency, which lags height in recovery.
Sequencing through rehab
- Early: IMTP (bilateral, then per-limb) and bilateral CMJ, once cleared for jumping. Track absolute force on the injured side.
- Mid: add single-leg CMJ. The per-limb comparison becomes the primary progression marker.
- Late: add drop jump and single-leg drop jump. Landing control and reactive strength are the final gates.
- Throughout: test at the same point in the week and after the same warm-up, so the time series is clean.
Reporting it
The report the surgeon, the coach and the athlete need is the same page: each test, injured versus uninjured, LSI, the strategy asymmetries, and a plain-language line per test. The report the physio needs adds the time series — where the injured limb is against its own history — because the question at each review is not only 'is it symmetric' but 'is it still improving'.
How Kinexis handles this
Kinexis tracks the injured versus uninjured limb on every test in this battery on one athlete profile, calculates LSI and the phase-specific asymmetries automatically, checks them against the thresholds your medical team sets, and writes the per-test line — so the return-to-sport review starts from a page, not from four exports.