Objective: To study associations of motor disability, physical activity, and muscle strength in older women, in particular to investigate whether model of spiraling decrease is expressed in the data.
Design: Cross-sectional analysis using data from the baseline measurements of The Women's Health and Aging Study (WHAS).
Setting: Participants' homes.
Participants: A total of 1,002 disabled women aged 65 years and older living in the community.
Outcome measures: Motor disability was measured by the number of self-reported difficulties in grasping, lifting 101b, walking across a small room, walking 1/4 mile, climbing 10 steps, and doing heavy housework. Level of physical activity was determined from response to a series of questions on the frequency and amount of common activities and physical exercise. Hand grip and knee extension forces were measured using portable hand-held dynamometers.
Results: Disability and physical activity were inversely associated, with inactivity being most common among the most disabled women. Those with poorer strength reported more difficulties in motor activities. Greater strength was found among the physically more active. In stratified analyses, the positive association of physical activity on knee extension strength was consistent across disability levels. Multiple regression analysis showed that both physical activity and muscle strength were significant predictors for severity of disability. Structural equation model (LISREL) showed that muscle strength had a mediating role between physical activity and disability; disability was associated with physical inactivity, which correlated with lower muscle strength, which was associated with greater degree of disability.
Conclusion: Even though causality cannot be confirmed in this cross-sectional analysis, our findings suggested a spiraling model of decline in which muscle strength has a significant role.