Instrument & interpretation
Equipment & metrics
From a single force plate to a full CDP booth and out to wearable IMUs and VR headsets — the hardware determines what you can measure. The metrics — equilibrium score, composite score, strategy score, latency time — translate the raw centre-of-pressure trace into clinically interpretable numbers.
Every posturography system shares a common root: a sensor that records body sway over time. The simplest is a stationary force plate, which computes the centre of pressure as it shifts under the feet. The most complex is the CDP booth, with a dual force plate, a movable platform and a movable visual surround.
Newer wearable systems substitute miniature inertial sensors for the force plate, trading some controlled-condition fidelity for portability and real-world measurement.
Static-platform measures — sway area, sway velocity, path length — distinguish healthy from impaired postural control and are well-reproduced between sessions, with test–retest reliability around 0.75–0.95 for most parameters.1,2 They are not, however, diagnostic of which sensory system is dysfunctional.
CDP equipment is more expensive and more discriminating. The NeuroCom® EquiTest is the most-cited commercial system; subsequent generations have added integration with EMG, video and motion capture. Calibration is the critical maintenance variable — force-plate drift and visual-surround timing both need periodic checks.4
The conceptual model underlying CDP interpretation is the sensorimotor integration framework, in which the central nervous system adaptively reweights its dependence on each sensory channel; Peterka's stabilogram-diffusion analysis maps the raw CoP signal back to those control parameters and predicts the SOT condition scores from first principles.3 This is why the equilibrium score and strategy score are interpretable — they map onto the underlying control variables, not just raw sway numbers.
The expanding wearable ecosystem now includes validated trunk-IMU systems like ISway, which match force-plate sway in a range of populations and unlock tele-rehabilitation use-cases.5 They are not a CDP replacement — IMUs cannot deliver sway-referenced visual surround perturbations — but a complement.
The hardware spectrum
Five modalities, by ascending capability and cost. Choose by the clinical question; the static plate is sometimes all that is needed.
| Modality | Principle | What it measures | Best for | Caveat | Cost |
|---|---|---|---|---|---|
| Static posturographyBertec® BalanceCheck, Tetrax™ | Fixed force plate records CoP sway during quiet stance. | Sway area, sway velocity, path length, frequency content. | Population screening, longitudinal tracking, low-resource clinics. | Cannot localise the sensory or motor system at fault. | low |
| Dynamic posturographyResearch and modified clinical platforms | Force plate plus controlled platform perturbations (translation, tilt). | Reactive postural responses to mechanical disturbance. | Selected research populations and tertiary referral centres. | Standardisation between sites is variable; protocols often custom. | medium |
| Computerized Dynamic PosturographyNeuroCom® EquiTest, SMART EquiTest, Pro-Kin | Dual force plates + sway-referenced visual surround under software control. | SOT (sensory weighting), MCT (motor latencies), ADT (adaptation), LoS (voluntary control). | Vestibular labs — sensory dependence, central vs peripheral, rehab planning. | Cost, footprint and trained-operator requirement limit accessibility. | high |
| Wearable IMU systemsAPDM Opal, BioStamp, smartphone accelerometry | Miniature inertial sensors over trunk / lower limb measure sway, gait and turning. | ISway-style sway, turn velocity, gait variability — across real-world settings. | Community testing, tele-rehabilitation, longitudinal Parkinson tracking. | Lacks the controlled sensory-conflict manipulations of CDP. | low |
| VR / AR-augmented testingHeadset + force plate / IMU systems (research and emerging clinical) | Virtual or augmented visual environments graded for optic flow and complexity. | Sway under controlled, immersive visual perturbation. | Visual-dependency syndromes (PPPD), graded desensitisation, paediatric engagement. | Equipment cost and motion-sickness risk; clinical evidence still building. | medium |
Inside the instruments
Tab through four representative systems to see what is actually under the bonnet — the CDP booth's dual plates and sway-referenced surround, the load cells of a static force plate, the IMU's belt-clip and three-axis sensor, and a VR-augmented setup pairing headset and platform.
NeuroCom EquiTest booth
The reference CDP system — dual force plate, sway-referenced visual surround, software-controlled platform tilt, overhead safety harness.
- Three-walled enclosure isolates the patient from ambient visual flow.
- Dual force plates (one per foot) compute mediolateral and anteroposterior CoP.
- Servo motors tilt the platform in sync with measured AP sway.
- Visual surround sways under software control to deliver SOT 3 and 6.
The four metrics that matter
- Equilibrium score (SOT, per condition)
- Percentage of the theoretical 12.5° sway envelope retained. Higher is better; 0 indicates a fall.
- Composite score (SOT, overall)
- Weighted average of the six condition scores. The single number used for inter-visit comparison.
- Strategy score (SOT, per condition)
- 0–100 measure of ankle (high) vs hip (low) strategy use. Drift towards hip strategy under low-difficulty conditions flags compensation or fear of falling.
- Latency time (MCT)
- Time from platform translation to corrective CoP movement. Prolonged values indicate central slowing or peripheral neuropathy.
Setting up reliably
- Foot placement: standardised stance width and 30° external rotation, per protocol.
- Footwear: consistent across visits — usually shoes off, or standardised flat shoes.
- Harness: a non-restrictive overhead harness for CDP. Catches falls without limiting sway.
- Environment: sound-attenuated, climate-controlled room; calibration before each session.
- Operator training: recognising artefacts (handrail touches, head movements, talking) is as important as running the protocol.