Criterion Validity and Between-Day Reliability of Three-Dimensional Motion Capture and the Perch Camera System for Monitoring Velocity During Weightlifting Derivatives

ABSTRACT: Wood, T, Creaby, MW, Nicholson, V, Cowley, N, Hebron, I, Schultz, L, Timmins, R, Brennan, TR, and Weakley, J. Criterion validity and between-day reliability of three-dimensional motion capture and the perch camera system for monitoring velocity during weightlifting derivatives. J Strength Cond Res 40(5): e445-e453, 2026-Monitoring bar velocity in resistance training is widespread and can be beneficial for performance, but it is vital to consider the validity and reliability of the technology used. Consequently, this study aimed to quantify the criterion validity and between-day reliability of the Perch device across 7 weightlifting derivatives. Following 2 sessions to determine 1 repetition maximum (1RMs) of the power snatch, hang power clean, hang power snatch, clean pull, snatch pull, hang clean pull, and hang snatch pull, 14 subjects completed repetitions at 20, 40, 60, 80, 90, and 100% of 1RM across 4 subsequent sessions under a 3-dimensional (3D) motion capture system. To evaluate criterion validity, R-squared and root mean square error were calculated with generalized estimating equations, and Bland-Altman plots assessed the magnitude of difference between measures. Between-day reliability was calculated with SEM and minimum detectable changes (MDC) for 3D motion capture and the Perch across repeated sessions. The Perch explained 86-96% of the variation in the criterion measure, showing nearly perfect linear relationships, but was consistently ∼0.25 m·s-1 slower than the criterion, suggesting a systematic difference between the 2 devices. The SEM ranged from 0.04 to 0.19 m·s-1 for 3D motion capture and 0.03-0.16 m·s-1 for the Perch. The MDCs ranged from 0.10 m·s-1 to 0.54 m·s-1 for 3D motion capture and 0.09 m·s-1 to 0.48 m·s-1 for the Perch. The Perch device can be used to reliably monitor training and provide feedback, which can support performance and physical adaptation.