title: Increasing ankle push-off work with a powered prosthesis does not necessarily reduce metabolic rate for transtibial amputees.
abstract: Amputees using passive ankle-foot prostheses tend to expend more metabolic energy during walking than non-amputees, and reducing this cost has been a central motivation for the development of active ankle-foot prostheses. Increased push-off work at the end of stance has been proposed as a way to reduce metabolic energy use, but the effects of push-off work have not been tested in isolation. In this experiment, participants with unilateral transtibial amputation (N=6) walked on a treadmill at a constant speed while wearing a powered prosthesis emulator. The prosthesis delivered different levels of ankle push-off work across conditions, ranging from the value for passive prostheses to double the value for non-amputee walking, while all other prosthesis mechanics were held constant. Participants completed six acclimation sessions prior to a data collection in which metabolic rate, kinematics, kinetics, muscle activity and user satisfaction were recorded. Metabolic rate was not affected by net prosthesis work rate (p=0.5; R2=0.007). Metabolic rate, gait mechanics and muscle activity varied widely across participants, but no participant had lower metabolic rate with higher levels of push-off work. User satisfaction was affected by push-off work (p=0.002), with participants preferring values of ankle push-off slightly higher than in non-amputee walking, possibly indicating other benefits. Restoring or augmenting ankle push-off work is not sufficient to improve energy economy for lower-limb amputees. Additional necessary conditions might include alternate timing or control, individualized tuning, or particular subject characteristics.
authors.affiliation: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA.
authors.forename: Roberto E
authors.initials: RE
authors.lastname: Quesada
authors.affiliation: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA; Human Motion Technologies L.L.C., Pittsburgh, PA, USA.
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Caputo
authors.affiliation: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA; Robotics Institute, Carnegie Mellon University, Pittsburgh, PA, USA. Electronic address: stevecollins@cmu.edu.
authors.forename: Steven H
authors.initials: SH
authors.lastname: Collins
mesh_terms: D000328:Adult; D000671:Amputation, Surgical; D000674:Amputees; D000842:Ankle / Q000503:physiopathology*; D000843:Ankle Joint / Q000503:physiopathology*; D001696:Biomechanical Phenomena; D004734:Energy Metabolism; D005684:Gait / Q000502:physiology; D006801:Humans; D007595:Joint Prosthesis; D008297:Male; D008875:Middle Aged; D017060:Patient Satisfaction
keywords: Amputation; Energetics; Gait; Robotics