Test-Retest Reliability of Postural Sway Measures Using a Portable Low-Cost Force Plate in Healthy Adults

Area of Science:

• Biomechanics and Motor Control
• Clinical Biomechanics
• Rehabilitation Technology

Background:

• Center of pressure (CoP) metrics from force plates are crucial for quantifying postural control.
• Laboratory-grade systems limit routine clinical and field use of CoP measurements.
• Portable, low-cost force plates offer potential for longitudinal balance monitoring by physiotherapists.

Purpose of the Study:

• To systematically compare the test-retest reliability of CoP outcomes using a portable low-cost force plate.
• To evaluate reliability across bipedal and single-leg stance conditions.
• To provide device- and task-specific validation data for clinical and field implementation.

Main Methods:

• Test-retest reliability study involving 27 healthy young adults over two sessions (7-10 days apart).
• Participants performed barefoot bipedal and single-leg quiet stance trials with standardized conditions.
• Relative (ICC) and absolute (TE, CV) reliability metrics were analyzed, alongside paired t-tests for systematic differences.

Main Results:

• Single-leg stance demonstrated substantially higher inter-session reliability (ICC 0.85-0.90 for displacement/velocity) compared to bipedal stance (ICC 0.39-0.65).
• CoP displacement and velocity measures during single-leg stance showed good to excellent reliability with low variability (CV ≈ 8%).
• Bipedal stance exhibited poor to moderate reliability, with excessive variability for ellipse area (CV > 60%).

Conclusions:

• Single-leg stance yields more reliable CoP measures than bipedal stance with portable low-cost force plates in healthy young adults.
• Displacement- and velocity-based CoP outcomes during single-leg stance are most suitable for repeated assessments and balance monitoring.
• MDC95 values represent measurement error thresholds and should not be mistaken for indicators of clinical change.