Concurrent Validity, Inra-unit, and Inter-unit Reliability of the Vmaxpro for Measuring Velocity

Abstract: The purpose of the present study was to evaluate the concurrent validity, intra-unit, and interunit reliability of the IMU Vmaxpro for measuring velocity for VBT purposes. Two protocols were constructed to cover velocities seen in the practical environment. Utilizing the 1080 Quantum the first protocol collected data without the use of subjects. For the second protocol, six well-trained men (age: 25.7 ± 4.2 years, standing height: 185.8 ± 10.6 cm, bodyweight: 87.3 ± 9.1 kg) performed loaded countermovement jumps. Two Vmaxpros and a 1080 Quantum simultaneously recorded repetitions for mean and peak velocity. Linear regression, RMSE, Bland-Altman, TE, and SDC were used to evaluate the concurrent validity, intra-unit, and inter-unit reliability. A strong relationship was found for MV and PV (R2 = 0.991– 0.997, RMSE = 0.044 – 0.05), p < 0.05) as well as a strong agreement on both protocols (bias: -0.039 – 0.072 on Protocol 1 and bias: 0.155 – - 0.005 on Protocol 2). The Vmaxpro showed strong reliability scores for within (MV: TE = 0.013 – 0.021; PV: TE = 0.017 – 0.023), and between sessions (MV: TE = 0.014 – 0.020; PV: TE = 0.019 – 0.027). Inter-unit reliability was acceptable to strong for both MV (TE = 0.012 – 0.034) and PV (TE = 0.021 – 0.057). The Vmaxpro can provide valid and reliable measurements for VBT purposes when using a single sensor. However, the inter-unit reliability showed a magnitude of variance which suggests practitioners not to use multiple devices interchangeably, and if so, it should be done with caution.