Does the impedance of above-knee powered prostheses need to be adjusted for load-carrying conditions?

Powered knee prostheses provide substantial advantages for amputees compared to traditional passive devices during basic walking tasks (i.e. level-ground, stairs, ramps), but the impedance control parameters are fixed. For environments that differ from the well-controlled setting of the clinic, amputees must compensate their gait patterns because fixed control parameters ideal for walking on level ground in the clinic do not meet real-life task demands. Load carriage is one instance where fixed control parameters may lead to undesired gait patterns and potentially result in injury. To evaluate the importance of impedance control parameters for different walking tasks, we tested one above-knee amputee walking using an experimental powered prosthesis under four walking conditions. The amputee walked with and without added mass with both load-specific and non-specific impedance control parameters. The load-specific parameters significantly reduced the amputee's intact-leg compensations, asymmetry, and perceived exertion compared to the non-specific control parameters. Powered lower limb prostheses that modulate impedance control parameters for load-carrying tasks may improve the gait performance, safety, and comfort of amputees.