Development and Preliminary Evaluation of a Bimodal Foot Prosthesis for Walking and Running.

People often alternate between bouts of walking and running, for instance, when adults participate in recreational activities. Transitioning between activities can be challenging for prosthesis users because existing prosthetic feet are not well-suited for both tasks. Meanwhile, switching between prostheses for different tasks is often impractical. Collectively, these challenges can present barriers to physical activity participation for people with limb loss, which can negatively impact social or physical health. This work describes the development and evaluation of a passive bimodal prosthetic foot prototype with different configurations and stiffnesses for walking and running. Users rated the bimodal prosthesis higher for standing and walking compared to a running prosthesis (+2.3 for both tasks on a seven-point Likert scale). Users rated the bimodal prosthesis higher for running compared to a walking prosthesis (+1.7 and +0.5 for 2.0 and 2.5 m/s running, respectively). Changing from walking to running mode increased the device's stiffness by 23-84%, depending on the user's preference. Users could switch between bimodal prosthesis walking and running modes quickly (21.3 ± 12.0 s). Overall, the preliminary results were encouraging in terms of user satisfaction, stiffness change between modes, and mode-switching speed. These findings motivate future exploration of this bimodal prosthesis concept.

Combining an Artificial Gastrocnemius and Powered Ankle Prosthesis: Effects on Transtibial Prosthesis User Gait.

Walking is more difficult for transtibial prosthesis users, partly due to a lack of calf muscle function. Powered ankle prostheses can partially restore calf muscle function, specifically push-off power from the soleus. But one limitation of a powered ankle is that emulating the soleus does not restore the multi-articular function of the gastrocnemius. This missing function may explain elevated hip and knee muscle demands observed in individuals walking on powered ankles. These elevated demands can make walking more fatiguing and impact mobility. Adding an Artificial Gastrocnemius to a powered ankle might improve gait for prosthesis users by reducing the prosthesis-side hip and knee demands. This work investigates if an Artificial Gastrocnemius reduced prosthesis-side hip or knee demands for individuals walking with a powered ankle providing high levels of push-off. We performed two case series studies that examined the effects that a passive elastic Artificial Gastrocnemius has on joint moment-impulses when prosthesis users walked with a powered ankle. We found that hip moment-impulse was reduced during stance when walking with an Artificial Gastrocnemius for six of seven participants. The Artificial Gastrocnemius effects on knee kinetics were variable and subject-specific, but in general, it did not reduce the knee flexor or extensor demands. The Artificial Gastrocnemius should be further explored to determine if reduced hip demands improve mobility or the user's quality of life by increasing the distance they can walk, increasing walking economy, or leading to increased physical activity or community engagement.