Decreasing the stiffness of an energy storage and return prosthetic foot improves propulsion but does so at the cost of stability, according to research from the University of Texas at Austin presented in August at the ASB meeting.
Investigators analyzed 12 unilateral transtibial amputees as they walked at 1.2 m/s under three prosthetic foot conditions featuring different levels of foot stiffness. The researchers used selective laser sintering to create a foot matching the stiffness of a typical carbon fiber ESAR foot, one with 50% more stiffness, and one with 50% less stiffness.
The more-compliant condition was associated with the highest levels of energy storage and return, but the lowest levels of mechanical efficiency. Residual limb plantar flexion moment and biceps femoris muscle activity in late stance phase significantly decreased as compliance increased, consistent with the prosthetic foot providing more propulsion.
However, less stiffness was also associated with increased braking forces and increased gluteus medius and vastus medialis muscle activity during late stance phase, indicating a need to compensate for lost stabilization.