Purpose: Physical inactivity is associated with an increased risk of various chronic health conditions that shortens disease-free life expectancy and decreases quality-adjusted life expectancy. However, we lack objective evidence on the patterns of habitual physical activity associated with healthy aging. One major problem is that most investigators have used questionnaires to ask about the frequency and/or duration of various types of physical activity during a typical recent week. Such instruments often take no account of weekly and seasonal variations in physical activity, and provide only limited estimates of the intensity and total volume of physical activity undertaken, particularly in older adults (who often have cognitive problems and difficulty in recalling recent events). The purposes of the current study were thus 1) to examine relationships between one objective measure of the quantity of habitual physical activity (the daily step count) and an assessment of its intensity (the daily duration of activity >3 metabolic equivalents [METs]) and 2) to explore interactive associations between the intensity and volume of habitual physical activity and health-related quality of life (HRQOL) in healthy free-living older adults. HRQOL is generally considered an important index of health and functional status in older populations. We hypothesized that HRQOL scores would be higher in elderly individuals in whom a larger proportion of their total daily activity was spent at an intensity >3 METs.
Methods: The participants were 74 male and 109 female volunteers aged 65-85 years. Criteria for recruitment included attendance at an annual medical examination, and the absence of chronic conditions that could limit physical activity or have a major effect on perceived quality of life. Participants gave their written informed consent to participation in this institutionally approved study, after the protocol, stresses, and possible risks had been fully explained to them. Step counts and the corresponding MET values were measured by pedometer/accelerometer throughout each 24-hr period for 1 year. At year-end, the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36) was used to assess HRQOL.
Results: The step count and the daily duration of physical activity at an intensity >3 METs were quite closely intercorrelated (quadratic r2 = .93, p < .05). After controlling for age, sex, and daily step count, the overall SF-36 score of participants taking approximately 7,000 steps/day was significantly higher in individuals who spent more rather than less of their total activity at an intensity >3 METs. Three categories of individual were distinguished, those who spent 25, 22, and 11 min/day at >3 METs. Engagement in activity >3 METs was associated more closely with the physical than with the mental components of the SF-36.
Conclusion: The associations we have observed suggest the importance of the intensity and thus the volume of physical activity to the HRQOL of older individuals. This issue should be evaluated further by longitudinal studies where subjects modify both their intensity and their total volume of physical activity.