Abstract
The muscles surrounding the ankle, knee and hip joints provide 42, 16 and 42%, respectively, of the total leg positive power required to walk on level ground at various speeds. However, each joint's contribution to leg work when walking up/downhill at a range of speeds is not known. Determining each biological joint's contribution to leg work over a range of speeds and slopes can inform the design of biomimetic assistive devices (i.e. prostheses). Twenty healthy adults walked 1.00, 1.25 and 1.50 m s−1 on 0°, ±3°, ±6° and ±9° while we collected kinematic and kinetic data. We calculated sagittal plane joint work and individual leg work over the entire stance phase. The ratio of ankle joint to total individual leg positive work (summed ankle, knee and hip joint work) did not change (0.42) with speed or slope, but the ratio of ankle joint to individual leg negative work was 0.38 at −9°, 0.42 at 0° and 0.27 at +9° across all speeds. The ratio of ankle joint to total individual leg negative work was 0.41 at 1.00 m s−1 and 0.32 at 1.50 m s−1 across all slopes. The ratio of knee joint to total individual positive leg work (0.22) did not change with speed or slope. The ratio of knee joint to total individual leg negative work was 0.39 at 1.00 m s−1 and 0.45 at 1.50 m s−1 across all slopes. The ratio of hip joint to total individual leg positive work did not change with speed but was 0.34 at −9°, 0.33 at 0° and 0.37 at +9° across all speeds. The ratio of hip joint to total individual leg negative work was 0.21 at 1.00 m s−1, and 0.24 at 1.50 m s−1 across all slopes and 0.17 at −9°, 0.19 at 0° and 0.29 at +9° across all speeds. The ankle significantly contributes to walking on slopes and this contribution changes during sloped compared with level-ground walking, thus assistive devices that provide biomimetic ankle function must adapt to accommodate walking at different speeds and slopes; whereas assistive biomimetic devices for the knee only need to adapt at different speeds.
Highlights
The net mechanical work done on the centre of mass (COM) during level-ground walking is presumably near zero over a stride
We determined the changes in ankle, knee and hip joint biomechanics during walking at different speeds and slopes and calculated sagittal plane individual leg work and joint work over the entire stance phase
The ratio of ankle joint to total individual leg positive work did not change with speed or slope, but the ratio of ankle joint to total individual leg negative work decreased with faster speed and steeper uphill slope
Summary
The net mechanical work done on the centre of mass (COM) during level-ground walking is presumably near zero over a stride. The biomechanics of the single support phase of walking have been described using an inverted pendulum model, where the body’s COM is represented by a point mass, and the leg by a rigid, massless strut [1,2,3,4] This model suggests that minimal external mechanical work is necessary to sustain steady-speed level-ground walking during single support because there is a constant phasic exchange of potential and kinetic energy [1,3]. Multiple studies have found that during level-ground walking at a constant speed, the net mechanical work done on the COM per step is approximately 0.22 J kg21 [5,6] and per stride is up to 4.0 J (0.05 J kg21) [7] These findings are probably due to mechanical work required during the step-to-step transition phase. Powered knee and ankle–foot prostheses have been developed to replicate normative walking mechanics by providing stance phase power primarily during the step-to-step transition [15]
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