Effects of age and functional limitation on leg joint power and work during stance phase of gait

It is commonly accepted that leg muscle power is an important component of functional ability. Paced gait data for 20 healthy young women (27+/-4.2 yrs), 16 healthy old women (72.5+/-5.6 yrs), and 24 functionally limited old women (73.5+/-7.2 yrs) were analyzed during stance phase to investigate whether power calculations from motion analysis data were sensitive to impairments beyond the differences expected with aging. Healthy women included in the study functioned at a high/moderate level with no limitations, while functionally limited women functioned at a much lower level and exhibited one or more functional limitations as defined by the SF36 physical function scale. Single support time (SSUP), stance duration (SDUR), average forward center of gravity velocity (GVEL), and three-dimensional net power and work of the ankle (APOW/AWRK), knee (KPOW/KWRK), and hip (HPOW/ HWRK) were computed for the stance limb during the stance phase of gait. Univariate ANCOVA was used to examine which variables were most sensitive to functional limitations. We found that SDUR and SSUP were not different among the three groups when controlling for height and weight. Although differences in CG velocity between healthy and functionally limited old women were not significant, both elderly groups translated their CG slower than did the younger women (p<0.0001) when walking at the same cadence. Controlling for CG velocity eliminated all significant differences among groups except for APOW and AWRK in late stance phase between healthy and functionally limited elderly women (p<0.003). These results suggest that decreased ankle plantar-flexor power in late stance of gait may be an impairment-related characteristic more than an age-related characteristic.