Functional roles of ankle and hip sagittal muscle moments in able-bodied gait

Objective. The main objectives of this study on able-bodied gait were (a) t o identify the main functions of the ankle and hip muscle moments and their contribution to support and propulsion tasks, and (b) to illustrate the in teraction between the ankle and hip moment activities. Design. Twenty young, able-bodied male subjects walked along a 13 m path at a freely chosen speed. Background. Functional contributions of the ankle and hip muscles and their interactions in achieving support and propulsion tasks during gait are sti ll subject to controversy. Methods. Principal component analysis was applied as a curve structure dete ction method to identify the main functional characteristics of the ankle a nd hip muscle moments. The first two principal components which contained o ver 70% and 85% respectively, of the information in the ankle and hip momen t curves revealed their functional tasks. Ankle versus hip moment plots was used to illustrate the interactions between muscles acting at the hip and ankle in the sagittal plane. Correlation coefficient and covariance calcula tions quantified the interaction between the ankle and hip moments. Results. The first principal component revealed that the main role of the a nkle and hip is to keep the body from collapsing. The second principal comp onent is associated with the functional contribution of both ankle plantarf lexors and hip flexors during the propulsion phase (50-60% of the gait cycl e). High coordination (r = 0.82) between the ankle and hip moments was obse rved. Conclusion. Maintaining body support against gravity was identified as the first functional task of the ankle plantarflexors and hip extensors, while contribution to propulsion was recognised as the second major role for the ankle plantarflexors and hip flexors.