title: Locomotor adaptation to a powered ankle-foot orthosis depends on control method.
abstract: BACKGROUND
  We studied human locomotor adaptation to powered ankle-foot orthoses with the intent of identifying differences between two different orthosis control methods. The first orthosis control method used a footswitch to provide bang-bang control (a kinematic 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 flexion 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 electromyography (EMG), joint kinematics, and orthosis kinetics. We compared stance phase EMG amplitudes, correlation of joint angle patterns, and mechanical work performed by the powered orthosis between the two controllers over time.
  
  
  RESULTS
  During steady state at the end of the second session, subjects using proportional 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 myoelectric 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 performed more negative work with the orthosis.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Biomedical Engineering, University of Michigan, 1107 Carl A, Gerstacker, 2200 Bonisteel Blvd,, Ann Arbor, MI 48109-2099, USA. smcain@umich.edu
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Cain
authors.forename: Keith E
authors.initials: KE
authors.lastname: Gordon
authors.forename: Daniel P
authors.initials: DP
authors.lastname: Ferris
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000842:Ankle / Q000502:physiology*; D001696:Biomechanical Phenomena; D035061:Control Groups; D004576:Electromyography / Q000379:methods; D005080:Exercise Test / Q000379:methods; D005260:Female; D005528:Foot; D006801:Humans; D016014:Linear Models; D008124:Locomotion / Q000502:physiology*; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology; D009989:Orthotic Devices; D011187:Posture; D013997:Time Factors