Valid and Reliable Barbell Velocity Estimation Using an Inertial Measurement Unit

The accurate assessment of the mean concentric barbell velocity (MCV) and its displacement are crucial aspects of resistance training. Therefore, the validity and reliability indicators of an easy-to-use inertial measurement unit (VmaxPro^®) were examined. Nineteen trained males (23.1 ± 3.2 years, 1.78 ± 0.08 m, 75.8 ± 9.8 kg; Squat 1-Repetition maximum (1RM): 114.8 ± 24.5 kg) performed squats and hip thrusts (3-5 sets, 30 repetitions total, 75% 1RM) on two separate days. The MCV and displacement were simultaneously measured using VmaxPro^® and a linear position transducer (Speed4Lift^®). Good to excellent intraclass correlation coefficients (0.91 < ICC < 0.96) with a small systematic bias (p < 0.001; η_p² < 0.50) for squats (0.01 ± 0.04 m·s^-1) and hip thrusts (0.01 ± 0.05 m·s^-1) and a low limit of agreement (LoA < 0.12 m·s^-1) indicated an acceptable validity. The within- and between-day reliability of the MCV revealed good ICCs (0.55 < ICC < 0.91) and a low LoA (<0.16 m·s^-1). Although the displacement revealed a systematic bias during squats (p < 0.001; η_p² < 0.10; 3.4 ± 3.4 cm), no bias was detectable during hip thrusts (p = 0.784; η_p² < 0.001; 0.3 ± 3.3 cm). The displacement showed moderate to good ICCs (0.43 to 0.95) but a high LoA (7.8 to 10.7 cm) for the validity and (within- and between-day) reliability of squats and hip thrusts. The VmaxPro^® is considered to be a valid and reliable tool for the MCV assessment.