Optimization of Active Backpack Loading Patterns to Improve the Walking Performance for Individuals With a Unilateral Transtibial Amputation

Individuals with unilateral transtibial amputation (TTA) often demonstrate asymmetrical gait patterns, which are further exacerbated during load carriage as passive prostheses cannot modulate their mechanical stiffness to accommodate the increased demand. Load carriage also increases the loads on the intact limb that can lead to overuse injuries and is also associated with increased metabolic cost and decreased forward propulsion. While active and passive load-suspended backpacks have been studied in healthy populations, no studies have explored the use of active backpacks to improve the walking performance for individuals with TTA. Therefore, the purpose of this study was to identify active backpack loading patterns to improve the metabolic cost, forward propulsion, and knee joint loading of individuals with TTA using a musculoskeletal simulation-based optimization framework. Different loading patterns were simulated using a time-varying actuator force applied to an active backpack over the gait cycle. The magnitude and timing of the actuator force were optimized for each performance criterion that resulted in a unique actuation pattern for each biomechanical measure. Interestingly, similar improvements relative to a passive backpack were observed across all actuation patterns, regardless of the optimization criteria. With all active backpacks, the force impulse experienced by the body from the dynamic load decreased, which resulted in increased forward propulsion, decreased intact knee joint loading, and improved metabolic cost. This suggests that active backpacks have the potential to improve walking performance during load carriage for individuals with TTA.