Effects Of Knee Exoskeleton On Balance And Knee Flexion Angles During Drop-landing And Movement Tests

A light-weight pneumatic-powered knee exoskeleton could augment Soldiers’ mobility and lifting capabilities. However, added weight/bulkiness and artificially produced knee extension torque could compromise sensorimotor characteristics (e.g., poor balance, stiffer landing, or limited joint range-of-motion [ROM]) PURPOSE: To compare balance characteristics and knee flexion angles during drop-landing and FMS tasks with (EXO) and without (NoEXO) wearing a knee exoskeleton. METHODS: Ten healthy Soldiers conducted three visits within 10 days to the biomechanics laboratory (familiarization, EXO, and NoEXO). Subjects were asked to complete the following tasks on each visit: single-leg balance, single-leg drop-landing from 12-inch height, and select FMS (overhead squat, hurdle step-over, rotary stability, lunge, and straight leg-raise). Balance characteristics (the ground reaction forces [GRF] variability and center-of-pressure [COP] velocity) were derived from force plates while knee flexion angles during drop-landing and FMS tasks were captured using an IMU-based motion capture system. Paired t-tests were used to compare between EXO and NoEXO conditions. RESULTS: The EXO condition showed increased GRF variabilities (EXO:3.5-7.2 N, NoEXO:3.0-6.0 N, p = 0.013-0.019) and decreased COP velocity (EXO:69.1-86.0 mm/s, NoEXO:76.2-92.6 mm/s, p = 0.001-0.017). During landing, the EXO condition showed lower knee flexion angle at the initial contact (EXO:7.0-10.1°, NoEXO:11.6-18.6°, p = 0.004-0.021) and peak (EXO:45.9-47.0°, NoEXO:52.7-55.1°, p = 0.006-0.01). Additionally, the EXO condition showed less knee flexion ROM during the overhead squat (EXO:108.1-112.9°, NoEXO:120.2-121.3, p = 0.007-0.033) and hurdle step-over (EXO:114.5-115.9°, NoEXO:125.7-127.1° p = 0.004-0.005). CONCLUSIONS: While wearing EXO, subjects exhibited stiffer landings (less knee flexion) and reduced available knee ROM during FMS. Given that these compromised sensorimotor characteristics have been associated with musculoskeletal injury risk, modifications to the EXO to facilitate knee flexion during dynamic activities may be warranted. Supported by MO21500/MO210170. The opinions expressed are the authors' and are not to be construed as official or as reflecting the views of the Army or Department of Defense.