Habitual Physical Activity and Physical Fitness in Older Japanese Adults: The Nakanojo Study

Background: Optimal patterns of habitual physical activity to ensure healthy aging remain unclear because of measurement limitations; most investigators have used either subjective questionnaires, or accelerometer or pedometer measurements limited to a single week, despite evidence of both the limited reliability/validity of questionnaires and seasonal changes in activity patterns. Objective: This study explored possible associations between indicators of physical fitness (walking ability, upper-and lower-extremity isometric strength, and static and dynamic balance) and yearlong pedometer/accelerometer assessments of the quantity and quality of habitual physical activity in ostensibly healthy older adults. Methods: Subjects were 76 male and 94 female Japanese aged 65-84 years. Each participant wore a pedometer/accelerometer for 1 year; measurements included the average number of steps taken each day and the duration of activity at an intensity of >3 metabolic equivalents (METs). Compliance was good, the instrument being removed for intervals of >3 h on <5% of days; data for such intervals were excluded from analysis. At the year's end, traditional laboratory techniques assessed preferred and maximal walking speeds, peak handgrip force, peak knee extension torque, total body sway, and maximal functional reach. Results: After controlling data for age and/or sex, lower-extremity function (walking speeds and knee extension torque) showed significant positive relationships with the daily step count and daily duration of activity at >3 METs, especially in individuals >= 75 years of age. On the other hand, handgrip force and body sway were unrelated to pedometer/accelerometer measurements. Linear and exponential regressions showed positive associations between walking speeds and pedometer/accelerometer scores up to the observed maxima of 13,700 steps/day and 62 min/day at >3 METs. However, when data were categorized into quartiles, walking speeds were not significantly greater in persons exceeding 7,000-8,000 steps/day and/or 15-20 min/day at >3 METs. With a few exceptions, subjects meeting these levels of habitual activity had walking speeds above the threshold predicting the development of functional dependence. Conclusion: The present data suggest that fitness is well maintained in elderly people who take >7,000-8,000 steps/day and/or spend >15-20 min/day at >3 METs. Nevertheless, the direction of this association merits exploration by longitudinal prospective studies and/or randomized controlled trials. Copyright (C) 2009 S. Karger AG, Basel