Concurrent validity of Strength By Numbers Stomp-IT force platforms for measuring strength, balance and jump movements

Portable force platforms are increasingly used in sport, exercise and rehabilitation settings, but system-specific validation is required before they are implemented for decision-making. This study assessed the concurrent validity of the Strength By Numbers Stomp-IT portable uniaxial dual force platform system against laboratory-based force platforms across selected upper-body strength, balance and jump tests. Eighteen physically active young adults completed three trials of the athletic shoulder test at 135 degrees, 30-s single-leg balance, countermovement jump, drop jump, and 10/5 repeated jump. Vertical ground reaction force and centre of pressure data were collected simultaneously from both force platform systems. Time-series agreement was assessed using root mean square error and Bland–Altman plots, while discrete metric agreement was assessed using relative differences and intraclass correlation coefficients. Force-time waveform agreement was strong across strength and jump tasks, while centre of pressure waveform agreement in balance tasks demonstrated greater variability, particularly in the mediolateral direction. Discrete metrics demonstrated generally strong agreement, with 92% of metrics showing good or excellent relative differences and 67% demonstrating good or excellent intraclass correlation coefficients. The Stomp-IT system appears valid for many common force-platform outcomes within the tested protocols, although metric-specific interpretation remains essential.