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; R=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.

Modular footwear that partially offsets downhill or uphill grades minimizes the metabolic cost of human walking

“…Despite the considerable range of tested shoe inclinations, the effects of shoe inclination were relatively shallow and outweighed by the effects of the treadmill grade. There was also high variability in the individual trends (electronic supplementary material, figure S7) similar to studies with exoskeletons and prostheses [62][63][64]. This interindividual variability is probably a combination of real differences in optimal footwear for each individual and trial-to-trial variability from noisy metabolic rate measurements.…”

Inclusion of actuator dynamics in simulations of assisted human movement

“…To date, an experimental study found that a powered foot‐ankle prosthesis was not able to reduce the metabolic cost below non‐amputee levels 11 . A similar experimental result was found in Reference 12, where an experimental powered foot‐ankle prosthesis emulator was not capable of approaching the metabolic cost of a person without amputation, despite being able to achieve higher than normal anatomical levels of ankle work. Although many elements likely contributed to differences between modeled and observed results, one cause may be that the device in the Handford and Srinivasan (2016) study produced large ankle torque impulses during late stance where most current prostheses are not capable of such high torques 11,13 .…”

Segmental contributions to sagittal-plane whole-body angular momentum when using powered compared to passive ankle-foot prostheses on ramps

“…Our results may also help explain why people with TTA prefer devices that deliver more ankle power than passive prostheses, despite evidence that the increased ankle push-off work does not necessarily reduce metabolic cost [22] and suggesting an alternative objective pertaining to balance [23]. Our results indicate that the powered prosthesis contributes a larger magnitude of H Trunk than a passive prosthesis, which should aid in walking and reduce metabolic cost.…”