(24) COMPARISON OF BARBELL VELOCITY BETWEEN TWO INERTIAL MEASUREMENT UNITS DURING BACK SQUAT AND BENCH PRESS

Purpose: To compare the mean velocity (MV), peak velocity (PV), and mean propulsive velocity (MPV) from two different inertial measurement units (IMU) affixed to a barbell during back squat and bench press in men and women. Methods: Thirteen resistance-trained men and women volunteered to complete an incremental loading protocol to predict their 1-repetition maximum (1RM) on barbell back squat and bench press, followed by sets to failure at 75% of their 1RM. The incremental loading protocol began with an unloaded standard barbell and was increased on subsequent sets until the barbell mean velocity decreased below 0.50 m/s. To predict 1RM, a linear regression was determined from the barbell mean velocity at one light load ( >0.7 m/s) and one heavier load (< 0.5 m/s) with 1RM being the load at 0.30 m/s and 0.17 m/s for squat and bench press, respectively. After a 10-minute rest, participants completed four sets of squat and bench press at 75% of their estimated 1RM with two minutes of rest between each set. Throughout the study, barbell velocity was measured with two different IMUs (Output Sports; OS and Enode Pro; EP) affixed to the barbell. The mean, peak, and MPV from each device were recorded for all completing repetitions throughout the study. A total of 770 repetitions from the sets to failure were recorded for analysis. Differences in MV, PV, and MPV between devices (OS vs EP) were assessed by exercise (Back Squat vs Bench Press) and gender (Men vs Women) with a 3-way mixed factorial ANOVA. Significant interactions and main effects were assessed with Bonferroni-adjusted post hoc pairwise comparisons. Alpha level was set at p< 0.05 and data were presented as mean±standard deviation. Results: A significant devicexexercise interaction (p< 0.001) was observed for MV with post hoc tests revealing the EP (0.44±0.09 m/s) recorded significantly great greater MV than OS (0.37±0.09 m/s) during back squat (p< 0.001), but not bench press (0.36±0.12 m/s vs 0.36±0.13 m/s; p=1.000). For PV, a significant 3-way interaction (p=0.001) was observed. Post hoc tests revealed that during back squat the EP recorded significantly greater PV than OS for men (0.81±0.17 m/s vs 0.68±0.17 m/s; p< 0.001) and women (0.69±0.15 m/s vs 0.61±0.16 m/s; p< 0.001); however, during bench press the EP recorded significantly lower PV than OS for men (0.56±0.18 m/s vs 0.66±0.16 m/s; p< 0.001) and women (0.42±0.11 m/s vs 0.50±0.08 m/s; p< 0.001). Furthermore, a significant 3-way interaction was observed for MPV (p< 0.001) with post hoc tests revealing EP recording greater MPV than OS during back squat for men (0.44±0.11 m/s vs 0.39±0.09 m/s; p< 0.001), back squat for women (0.41±0.09 m/s vs 0.35±0.09 m/s; p< 0.001), and bench press for men (0.45±0.15 m/s vs 0.39±0.13 m/s; p< 0.001). However, no difference between EP and OS MPV during bench press for women (0.31±0.07 m/s vs 0.30±0.07 m/s; p=1.000). Conclusions: The two IMUs recorded significantly different barbell MV, PV, and MPV data during back squat and bench press sets to failure at 75% 1RM. The magnitude of disagreement between IMUs appear to be greater during back squat than bench press particularly for measuring MV. Practical Applications: Despite both IMUs being previously validated with acceptable reliability, they should not be used interchangeably by practitioners or researchers. Furthermore, caution should be taken when comparing barbell velocity data to previously published normative data collected with a different device. Acknowledgements: None