Comparison of the MetricVBT App and the Vitruve Linear Position Transducer for Assessing Execution Velocity and ROM

Background: The primary aim of this study is to evaluate the concurrent validity and practical applicability of the MetricVBT smartphone application compared with the Vitruve linear position transducer (VitruveLPT) for measuring mean velocity (MV) and peak velocity (PV) at one-repetition maximum (1-RM) during the Smith machine bench press (SMBP). A secondary aim is to assess the range of motion (ROM). Methods: Eighteen resistance-trained men completed a single 1-RM SMBP exercise test, with barbell kinematics simultaneously recorded using VitruveLPT and MetricVBT. Between-device differences were assessed using Wilcoxon signed-rank and paired-sample t-tests with Bonferroni correction (α ≤ 0.05). Associations were examined using Spearman's (ρ) and Pearson's (r) correlations, and absolute agreement was evaluated via intraclass correlation coefficients (ICC) and Bland-Altman analyses. Results: Significant differences were observed for MV (p = 0.026), but not for PV (p = 0.143) or ROM (p = 0.130). PV showed a very high correlation (r = 0.91, p < 0.001), whereas MV (ρ = 0.65, p = 0.002) and ROM (ρ = 0.55, p = 0.018) demonstrated moderate correlations. Agreement was good for PV (ICC = 0.888), moderate for MV (ICC = 0.612), and poor for ROM (ICC = 0.236). Mean bias was small for MV (-0.02 m·s^-1) and PV (0.02 m·s^-1), whereas ROM showed a larger bias (1.64 cm) and wide limits-of-agreement (LoA) for all variables (MV: -0.07 to 0.04 m·s^-1; PV: -0.08 to 0.11 m·s^-1; ROM: -13.82 to 17.10 cm). Conclusions: Although no statistically significant differences were observed, MetricVBT did not meet the reliability criteria for velocity monitoring. Despite small mean bias, the wide LoA for MV, PV, and ROM indicates that MetricVBT and VitruveLPT are not interchangeable for assessing performance parameters.