Objective To evaluate the concurrent validity and test-retest reliability of common movement, strength, and balance tests using portable uniaxial dual force plates. Design Repeated measures cross-sectional study. Methods Sixteen healthy individuals participated in two testing sessions, where they performed 12 different movement, strength, and balance tests. Vertical ground reaction forces (GRF) and centre of pressure (COP) data were collected using the VALD ForceDecks simultaneously with ground-embedded laboratory force plates. Concurrent validity was assessed by quantifying the agreement between force plate systems using root mean square error for raw time-series data and Bland-Altman plots for discrete metrics. Test-retest reliability was assessed using intraclass correlation coefficients (ICC) and minimal detectable changes. Results ForceDecks recorded vertical GRF and COP with high accuracy compared to laboratory force plates. The mean bias between systems was negligible (< 2N or 0.1mm), with small limits of agreement (< 5N or 1mm). Of all possible discrete force and COP metrics, 530/674 (79%) showed good or excellent validity (< 10% difference) and 611/773 (79%) had good or excellent reliability (ICC>0.75). ForceDecks reliability was similar to laboratory force plates (< 0.07 ICC median difference for all metrics). Conclusions Portable uniaxial force plates record highly accurate vertical GRF and COP during a range of movement, strength, and balance tests. The VALD ForcDecks are a valid and reliable alternative to laboratory force plates when strict standardized testing and data analysis procedures are followed. Users should be aware of the validity and reliability characteristics of the tests and metrics they choose.
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