This work transformed our understanding of gait, since previously (before computerized video analysis) the ankle was thought to be relatively unimportant for propulsion (Perry, 1992).

Winter's reports of the joint powers slow, natural and fast cadences (see graphs below from page 48 of his 1991 book) seem to indicate an increase in all power bursts at higher speeds - in particular, the A2 burst appears to be almost directly proportional to speed.

In 1997, Chen published the results of his 3D study of ten healthy children, in which he calculated the energy contribution of each joint to propulsion, as the area under the positive, concentric part, of the power curve at three speeds. It can be seen that, although the ankle energy is predominant at low speeds, the contributions of the hip and knee become progressively more important at higher speeds. In fact, ankle push-off seems to remain roughly constant.

Walking Speed	Ankle (A2)	Knee (K2)	Hip (H1+H3)	Total
Slow (J/kg)	0.22	0.04	0.08	0.35
% Total	63	11	23
Natural (J/kg)	0.21	0.06	0.12	0.39
% Total	54	15	31
Fast (J/kg)	0.19	0.10	0.15	0.45
% Total	42	22	33

• Do you agree with Perry or Winter?
• What is the purpose of the A2 push-off burst?
• Do you agree that it remains constant as walking speed increases?
• Why should the knee and hip be favored progressively as speed is increased?
• Does you lab routinely adjust its normative data to account for changes in walking speed?

Bibliography

Kirtley C & Whittle MW (1985) Influence of Walking Speed on Gait Parameters. Journal of Biomedical Engineering, 7: 282-288.

Perry J. (1992). Gait Analysis Normal and Pathological Function. Slack, Inc, Thorofare, NJ.

Winter DA (1983) Energy generation and absorption at the ankle and knee during fast, natural, and slow cadences. Clin Orthop. May;(175):147-54.

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