In this study, tasks of the hip in elderly and young gait were identified using principal-component analysis (PCA). Discrepancies between older and younger participants for hip-flexor and -extensor action during stance were also investigated. PCA was applied to the sagittal-hip-muscle-power curves of participants. Three principal components (PCs) were retained for further analysis. A t test revealed that all measures of gait spatiotemporal parameters were significantly lower in the older participants (p < .05). The first PC for both groups extracted the largest variation and described hip-power action during midistance. The second and third PCs in the older participants highlighted the role of the hip extensors and flexors during weight acceptance, late stance, and pull-off. The corresponding PCs for the younger participants were mainly associated with hip-extensor/flexor action during pull-off and weight acceptance. The results indicate that the hip-extensor/flexor muscles are mainly responsible for balance control in elderly gait but contribute to both balance control and propulsion in the gait of younger individuals.
Sadeghi and Zabjek are with the Research Center, Sainle-Justine Hospital, Montreal, Quebec, H3T 1C5 Canada. Prince and Allard (also Sadeghi) are with the Department of Kinesiology at the University of Montreal. Sadeghi is also with the Kinesiology Department at Tarbiat Moallem University, Ministry of Sciences, Research and Technology, Tehran. I.R. Iran.