Increasing ankle push-off work with a powered prosthesis does not necessarily reduce metabolic rate for transtibial amputees

J Biomech. 2016 Oct 3;49(14):3452-3459. doi: 10.1016/j.jbiomech.2016.09.015. Epub 2016 Sep 21.


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.

Keywords: Amputation; Energetics; Gait; Robotics.

MeSH terms

  • Adult
  • Amputation
  • Amputees
  • Ankle / physiopathology*
  • Ankle Joint / physiopathology*
  • Biomechanical Phenomena
  • Energy Metabolism
  • Gait / physiology
  • Humans
  • Joint Prosthesis*
  • Male
  • Middle Aged
  • Patient Satisfaction