Relationship between physical activity, knee muscle strength, and gait performance in persons with late effects of polio.

OBJECTIVE To examine the relationship between physical activity (assessed subjectively and objectively), knee muscle strength, gait performance, age, gender, and body mass index (BMI) in persons with late effects of polio. DESIGN Cross-sectional. SETTING A university hospital outpatient clinic. PARTICIPANTS Seventy-seven community-dwelling ambulant persons with late effects of polio (42 men and 35 women; mean age 67 years [standard deviation 6, range 54-80]). MAIN OUTCOME MEASURES Physical activity was described by the Physical Activity and Disability Survey and by a pedometer (number of steps/day). Isokinetic concentric knee extensor and flexor muscle strength was measured at 60°/s. Gait performance was assessed by the Timed "Up and Go" test, the Comfortable Gait Speed and Fast Gait Speed tests, and the 6-Minute Walk test. RESULTS The Physical Activity and Disability Survey leisure subscale was significantly correlated with all knee muscle strength measurements (P < .01), the Comfortable Gait Speed test (P < .05), and the 6-Minute Walk test (P < .05), and the number of steps per day was significantly correlated with all knee muscle strength measurements and all gait performance tests (P < .01). In the linear regression analyses, knee muscle strength and gait performance explained 1% to 8% of the variance in the leisure subscale, and when the personal attributes (age, gender, and BMI) were added, they explained up to 14% of the variance. Knee muscle strength explained 16% and gait performance explained 15% to 31% of the variance in the number of steps per day, and when personal attributes (age, gender, and BMI) were added, they contributed at most an additional 3% of the variance. CONCLUSIONS In ambulatory persons with late effects of polio, knee muscle strength and gait performance explain only a small portion of physical activity. Further studies are needed to increase our understanding of how other impairments, activity limitations, environmental factors, and personal factors are associated with physical activity in persons with late effects of polio.