Alterations In Gait Parameters During A Timed Ruck March Using A Single Inertial Measurement Unit

Alterations in Gait Parameters During a Timed Ruck March Using A Single Inertial Measurement Unit Peter D. Finch, Vanessa J. Ramirez, Kyla A. Driver, Rebecca E. Fellin, and Mark J. Buller U.S. Army Research Institute of Environmental Medicine, Natick, MA and Soldier Effectiveness Directorate, U.S. Army Combat Capabilities Development Command Soldier Center, Natick, MAMusculoskeletal injuries (MSKIs) are the main threat to Army readiness and Soldier health. Ruck marching and running are primary sources for knee, low back, and ankle injuries. Identifying gait changes with unobstructive equipment may provide an opportunity for early MSKI mitigation. PURPOSE: The purpose of this study is to examine gait parameters and how they changed over the course of a timed ruck march. METHODS: Nineteen male Soldiers (mean ± SD; age = 24.3 ± 3.0 years; height = 1.77 ± 0.07 m; weight = 81.2 ± 8.4 kg), took part in a timed (complete under 3-hours) 12-mile ruck march with combat load (27.2 kg). One inertial measurement unit (IMU) (APDM, Portland, OR), was placed on the left medial shank above the boot line. Step length, stance time, and cadence were measured. Yaw, the twisting around the vertical axis, tibial external rotation, was derived from the magnetometer data. Change in gait over time was examined during flat and uphill (> 3%) segments near the start and end of the march route. For each set of march segments (flat or uphill), variable means (SD) were compared using a paired t-test, with α < 0.05. RESULTS: There were no differences in cadence and stance time. Yaw did not change on the flat terrain but increased 2.1° (95% CI:0.52-3.78), p = 0.006) on the last uphill segment compared to the first. Step length decreased at the end of the course for both the flat (mean difference: 0.06 m (95% CI:0.02-0.12), p = 0.01) and uphill segments (mean difference: 0.05 m (95% CI:0.02-0.09), p = 0.008). CONCLUSIONS: An IMU detected meaningful changes in gait during a timed ruck march, including increased yaw and decreased step length from the first uphill segment to the second. Changes in tibial rotation elucidate changes in hip and ankle rotation, which are both moderate predictors for injury risk during prolonged ambulatory tasks. Disclaimer: The opinions here are the private views of the author(s) and do not reflect the views of the Army, the DOD, or the U.S. Government.