Poster P4 - Impact of an Active Ankle Exoskeleton on the Biomechanics of Healthy Men during Prolonged Walking

Introduction: Active lower-body exoskeletons can decrease the energy requirement of lower-body muscles by providing mechanical assistance (e.g., torque) at various joints, however, they also alter gait kinematics and kinetics. To date, we still do not know how prolonged use of such exoskeletons alters gait dynamics, especially with load carriage, and whether the resulting changes are detrimental or beneficial.

Materials and

Methods: We investigated the impact of prolonged exoskeleton use with load carriage on the walking biomechanics of men. We collected computed tomography images, electromyography (EMG) data, and motion-capture data for young, healthy men (N = 5) as they walked on an instrumented treadmill at 1.34 m/s for 5 km (~60 minutes) while carrying a 22.7-kg load, with and without an active ankle exoskeleton (the ExoBoot EB60). The ExoBoot applied a user-specific torque at the participants’ ankle joint and its magnitude was determined by their individual gait. Using this data, we developed individualized musculoskeletal models and computed various spatiotemporal parameters, such as stride length, and joint biomechanical parameters (joint angles, forces, and moments) for each participant under each walking condition (Figure 1). We then performed a non-parametric Wilcoxon rank sum test with Holm-Bonferroni correction to determine which biomechanical parameters significantly changed between walking 0 km and 5 km, both with and without wearing ExoBoot.

Results, Conclusions, and Discussions:

Results: While carrying a 22.7-kg load, without the ExoBoot device, the peak trunk flexion angle at 5 km compared to 0 km increased significantly between 8-113% and the stride length increased between 3-7% in at least 4 out of 5 participants. The same two parameters also increased when walking with the ExoBoot device, however, the average increases were smaller and ranged between 20-40% for the peak trunk flexion angle and 1-3% for the stride length. Expectedly, compared to without it, ExoBoot use significantly increased the ankle plantarflexion angle (12-64%) in the majority of the participants at 5 km. In addition, ExoBoot use also significantly altered three hip-related biomechanical parameters, i.e., on average, increased the peak hip abduction angle by 22% and hip extension angle by 13%, and decreased the hip flexion angle by 9%, after walking 5 km compared to 0 km.

Conclusion: We performed a pilot study and quantitatively assessed the potential impact of an active ankle exoskeleton device on the lower-limb biomechanics of young, healthy men due to walking with load carriage for 5 km (~60 minutes). We found that, during prolonged walking with load, ExoBoot use may mitigate the effects of fatigue-induced changes by lowering the magnitude of the increase in peak trunk flexion angle and stride length compared to unassisted walking. In addition, our analysis identified specific hip-related angles (hip extension, hip flexion, and hip abduction angles) that were significantly altered due to prolonged ExoBoot use. Thus, by identifying which specific gait-related parameters are most susceptible to change during prolonged use of exoskeleton devices, our study offers potential insights into the parameters that should be further evaluated for association with lower-leg musculoskeletal injuries. Such knowledge will ultimately inform the development of standards for safe and effective use of emerging exoskeleton technologies.

Acknowledgements (Optional): Acknowledgements: This work was sponsored by the Military Operational Medicine Program Area Directorate of the U.S. Army Medical Research and Development Command (USAMRDC), Fort Detrick, MD. The Henry M. Jackson Foundation was supported by the USAMRDC under Contract No. W81XWH20C0031. In addition, we acknowledge support from the Department of Defense High Performance Computing Modernization Program.

Disclaimer: The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the U.S. Army, the U.S. Department of Defense, or The Henry M. Jackson Foundation for the Advancement of Military Medicine, Inc. This abstract has been approved for public release with unlimited distribution.