Accuracy Of Inertial Measurement Units For Quantifying Kinematics During The Army Combat Fitness Test Deadlift

BACKGROUND: The hex bar deadlift (HDL) is a critical component of the Army Combat Fitness Test. Due to the risk of injury to the pelvis and spine there is a need for remote kinematic data collection in tactical environments. Optical motion capture (OMC) serves as the gold standard for collecting kinematic data, however their restriction to a laboratory limits application in tactical settings. The purpose of this study is to compare the compatibility of inertial measurement units (IMU) and OMC tracking of trunk, pelvis, and thigh orientations during three phases of the HDL under two loads. METHODS: Nineteen healthy active-duty soldiers (12 M, 7F) performed HDL at 85 and 93% of their estimated one repetition maximum (RM) based on their most recent three RM. IMU and OMC marker clusters were secured to the participants’ thighs, pelvis, and upper-spine to record sagittal plane trunk/pelvis segment angles and trunk-pelvis and pelvis-thigh relative angles. Based upon total trunk displacement, the concentric phase of three repetitions at each load was divided into three phases. The root mean square differences (RMSD) between IMU and OMC tracking were computed. T-tests were conducted for each RMSD to determine if IMU-OMC deviations significantly differed from zero followed by separate load by segment analyses of variance conducted on each angle. RESULTS: All RMSD values were significantly different from zero (P < .001, d = 1.1 to 1.6). No significant differences were revealed for either the trunk (P > .217) or pelvis (P > .209) segment angles with overall RMSD of 2.2 ± 1.9° and 2.2 ± 1.34° for the trunk and pelvis segment angles, respectively. For the trunk-pelvis relative angle, there were no significant differences (P > .232) with an overall RMSD of 2.8 ± 2.4°. Load had no significant effect on the pelvis-thigh relative angle (P > .189), whereas the RMSD was found to be significantly greater for the first phase (8.5 ± 6.3°), compared to the second (5.2 ± 3.4°, P = .004, d = .62) and third (5.0 ± 3.5°, P = .010, d = .65) phases. CONCLUSIONS: While IMU-OMC differed significantly, the discrepancy magnitudes between the two systems remained constant, therefore demonstrating that portable IMU systems may serve as a preferred data collection method in remote settings. Supported by: The study was funded by MOMRP MO230055. The authors declare no conflicts of interest or financial affiliations with any products used in the study. The views expressed in this manuscript do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.