Article

In an effort to improve amputee gait, energy storage and return (ESAR) prosthetic
feet have been developed to provide enhanced function by storing and returning
mechanical energy through elastic structures. However, the effect of ESAR feet on
muscle activity in amputee walking is not well understood. Previous studies have
analyzed commercial prosthetic feet with a wide range of material properties and
geometries, making it difficult to associate specific ESAR properties with
changes in muscle activity. In contrast, prosthetic ankles offer a systematic way
to manipulate ESAR properties while keeping the prosthetic heel and keel geometry
intact. In the present study, ESAR ankles were added to a Seattle Lightfoot2 to
carefully control the energy storage and return by altering the ankle stiffness
and orientation in order to identify its effect on lower extremity muscle
activity during below-knee amputee walking. A total of five foot conditions were
analyzed: solid ankle (SA), stiff forward-facing ankle (FA), compliant FA, stiff
reverse-facing ankle (RA) and compliant RA. The ESAR ankles decreased the
activity of muscles that contribute to body forward propulsion and increased the
activity of muscles that provide body support. The compliant ankles generally
caused a greater change in muscle activity than the stiff ankles, but without a
corresponding increase in energy return. Ankle orientation also had an effect,
with RA generally causing a lower change in muscle activity than FA. These
results highlight the influence of ESAR stiffness on muscle activity and the
importance of prescribing appropriate prosthetic foot stiffness to improve
rehabilitation outcomes.
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