The Association between Physical Activity and Lower Extremity Strength in Older Persons

Background and aim: Age-related physiological changes are well documented, such as loss of muscle fibers and muscle strength. Although there are many studies documenting the effect of resistance training on lower extremity strength, there has been less focus on the effect of general daily-life physical activity on lower extremity strength. The main purpose of the present study is therefore to investigate whether there is an association between general physical activity and lower extremity strength. Secondary aims are to investigate whether the relationship is different for self-reported and directly measured estimates of physical activity, for different estimates of lower extremity strength, and for different levels of physical activity. Possible gender differences will also be investigated. Methods: 486 men and women (mean age 71.5) performed a concentric functional chair rise task, Sit-to-Stand test, and an isometric leg press task as estimates of lower extremity strength. The participants filled out a questionnaire about physical activity based on the HUNT survey. Physical activity level was also measured directly using ActiGraph GT3X accelerometers. Results: There was a significant moderate association between the directly measured vertical acceleration and the movement of chair rise, and the intensity of daily physical activity and movement of chair rise. There was also a strong association between the parameters derived from ActiGraph, and moderate to strong associations between some of the questionnaire parameters. Between ActiGraph and the questionnaire parameters, there is a moderate association between the total number of activity minutes per week and vertical acceleration. In addition there was a moderate association between at least 30 minutes of activity per day and acceleration in all three directions. For the lower extremity strength parameters there was a strong association both within and across the different parameters for two tasks. Both genders reported to be less active than when their daily activity was directly measured by accelerometer. The men were more physically active and stronger in the lower extremities than the women. There was also an association between physical activity and lower extremity strength for both genders, but the association is stronger with respect to the men. Conclusion: There is an association between physical activity and lower extremity strength. There were significant findings for all of the paratmeters, but there was only a moderate association between both directly measured and self-reported physical activity and movement of chair rise. Finally, the participants are a rather active group, but tend to underestimate their activity level. There is also an association between physical activity and lower extremity strength for both genders