Concurrent validity of a dual three-dimensional portable force-plate system against a laboratory force platform across vertical, anteroposterior and mediolateral loading tasks.

INTRODUCTION: Portable three-dimensional (3D) force-plates are increasingly used for field measurements of sport performance. The purpose of the study was to evaluate the concurrent validity of a dual portable 3D force-plate system (KINVENT 3D-Deltas) against a single laboratory force-plate (AMTI) for the vertical, anteroposterior (AP), and mediolateral (ML) force components and for center-of-pressure (CoP) outcomes. METHODS: Ten physically active participants performed four tasks, each loading a specific axis: a countermovement jump (CMJ; vertical), a forward jump (AP), and a lateral jump (ML). Additionally, a quiet-stance trial was performed to validate CoP kinematics. The AMTI force-plate was mounted on top of the 3D-Deltas so that both systems recorded each trial simultaneously. Agreement was quantified with mean bias and 95% limits of agreement, the intraclass correlation coefficient (ICC; two-way random effects, absolute agreement, single measures), Pearson correlation, ordinary-least-squares regression, the root-mean-square error and paired-samples t-tests. RESULTS: Agreement for the primary force component of each task was excellent (CMJ: peak vertical force, ICC = 0.999; forward jump: peak AP force, ICC = 0.994; lateral jump: peak ML force, ICC = 0.999; each with a mean bias below 2.5% of the criterion). CoP excursion outcomes (AP range, ML range, and 95% confidence ellipse area) showed good-to-excellent agreement (ICC = 0.966-0.998). Secondary low-amplitude off-axis force components showed larger relative error. DISCUSSION: The KINVENT 3D-Deltas system is a valid surrogate for a laboratory force-plate when measuring the principal force component of each task and the principal CoP excursion outcomes, supporting its use for field performance assessments.