The non-disabled human ankle joint was examined during walking in an attempt to determine overall system characteristics for use in the design of ankle prostheses. The hypothesis of the study was that the quasi-stiffness of the ankle changes when walking at different walking speeds. The hypothesis was examined using sagittal plane ankle moment versus ankle angle curves from 24 able-bodied subjects walking over a range of speeds. The slopes of the moment versus ankle angle curves (quasi-stiffness) during loading appeared to change as speed was increased and the relationship between the moment and angle during loading became increasingly non-linear. The loading and unloading portions of the moment versus angle curves showed clockwise loops (hysteresis) at self-selected slow speeds that reduced essentially to zero as the speed increased to self-selected normal speeds. Above self-selected normal speeds, the loops started to traverse a counter-clockwise path that increased in area as the speed was increased. These characteristics imply that the human ankle joint could be effectively replaced with a rotational spring and damper for slow to normal walking speeds. However, to mimic the characteristics of the human ankle during walking at fast speeds, an augmented system would be necessary. This notion is supported by the sign of the ankle power at the time of opposite heel contact, which was negative for slow speeds, was near zero at normal speeds, and was positive for fast walking speeds.
Bibliographical noteFunding Information:
The authors would like to acknowledge the use of the VA Chicago Motion Analysis Research Laboratory of the VA Health Care System, Lakeside Division, Chicago, IL. The work described in the paper was supported by the Department of Veterans Affairs, Rehabilitation Research and Development Service and is administered through the VA Health Care System, Lakeside Division, Chicago, IL. This work was also funded by the National Institute on Disability and Rehabilitation Research (NIDRR) of the US Department of Education under Grant No. H133E980023. The opinions contained in this publication are those of the grantee and do not necessarily reflect those of the Department of Education or the Department of Veterans Affairs.
- Prosthetic ankle