Background: The usage of the Force-Velocity relationship for individualizing training regimes for athletes has increased in popularity. This can be done through measurements of muscle mechanical properties and creating individual force-velocity profiles. To do this, one must use valid and reliable test equipment. These types of equipment are often expensive and impractical, which limits the usage to a small population with the right financial means. Therefore, the purpose of this study was to examine the concurrent validity of the inertial sensor Vmaxpro for measuring muscle mechanical properties. Method: 52 male ice-hockey players (age:17.9 ± 2.2 years, body weight: 77.7 ± 10.6 kg, height: 180.3 ± 6.2 cm) participated in this study and performed two jumps each on four different loading conditions (unloaded, 25, 50 and 75% of BW). The jumps were recorded simultaneously with an inertial sensor and a linear transducer. Three different variables were analyzed: peak velocity (pV), average velocity (avgV) and average power (avgP). Pearson’s correlation coefficient (r), linear regression analysis, Bland-Altman analysis, and standard error of estimate (SEE) was used to examine the concurrent validity. Results: The results showed a strong correlation, agreement and small SEE for pV: r=0.98, bias = -0.12, SEE = 0.08, for avgV: r=0.98 bias = 0.01, SEE = 0.04 and for avgP: r = 0.97, bias = 30.94, SEE = 73.47. Practical application: The results from the present study indicate that the Vmaxpro can be used for assessing muscle mechanical properties. Furthermore, since the Vmaxpro is both cheap and portable, it can potentially expand the usage of test equipment to clubs and associations with limited budgets.

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.