Background: We studied human locomotor adaptation to powered ankle-foot orthoses with the intent of identifying differences between two different orthosis con-trol methods. The first orthosis control method used a footswitch to provide bang-bang control (a kinema-tic control) and the second orthosis control method used a proportional myoelectric signal from the soleus (a physiological control). Both controllers activated an artificial pneumatic muscle providing plantar fle-xion torque.Methods: Subjects walked on a treadmill for two thirty-minute sessions spaced three days apart under either footswitch control (n = 6) or myoelectric control (n = 6). We recorded lower limb electro-myography (EMG), joint kinematics, and orthosis kinetics. We compared stance phase EMG amplitudes, correla-tion of joint angle patterns, and mechanical work performed by the powered orthosis between the two con-trollers over time. Results: During steady state at the end of the second session, subjects using propor-tional myoelectric control had much lower soleus and gastrocnemius activation than the subjects using footswitch control. The substantial decrease in triceps surae recruitment allowed the proportional myoelec-tric control subjects to walk with ankle kinematics close to normal and reduce negative work performed by the orthosis. The footswitch control subjects walked with substantially perturbed ankle kinematics and per-formed more negative work with the orthosis. Conclusion: These results provide evidence that the choice of orthosis control method can greatly alter how humans adapt to powered orthosis assistance during walking. Specifically, proportional myoelectric control results in larger reductions in muscle activation and gait
kinematics more similar to normal compared to footswitch control.

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