Assessment of health-enhancing physical activity at population level

To assess the levels and patterns of health-enhancing physical activity in the population there is a real need for better instruments to be developed. The overall aims of this thesis were to test the International Physical Activity Questionnaire (IPAQ) and to study the level of health-enhancing physical activity in the Swedish adult population using both the IPAQ (a subjective method) and accelerometry (an objective method). To validate the IPAQ, data was collected from a convenience sample of 46 adult men and women. In a second study data was collected from 980 men and women, aged 18 - 65, randomly chosen from a population register. The IPAQ data was compared against data from an accelerometer and a logbook for concurrent validity, and body composition and aerobic fitness for construct validity. For the population based studies two nationally representative samples of adult men and women were used (N = 1,470 and N = 1,114). The validation studies showed significant correlations between the IPAQ and the accelerometer and logbook, although large intra-individual differences were found. Vigorous intensity activity and time spent in inactivity were systematically overreported with IPAQ. The IPAQ data showed that adults reported a median (25th - 75th percentile) of 1,699 (693 - 3,600) MET-min.week-1. This corresponds to about 60 (24 - 128) minutes of brisk walking per day. Men reported significantly more activity than women (1,836 vs. 1,554 MET-min.week-1, P < 0.001). A significant difference in total physical activity was found across age, BMI and self-rated health categories. For men, walking contributed 35 % (11 - 73 %) of the total physical activity, while for women, walking contributed 45 % (22 - 92 %). The accelerometer data showed that men were significantly more active on moderate or higher intensity level than women. For total physical activity and time spent in inactivity, neither gender, age nor BMI could explain the variance. More than half (52 %) of the study population reached the 30 minutes per day recommendation when every minute at moderate or higher intensity was counted. When activity bouts of 10 minutes or longer were considered, the prevalence estimates were only one percent. This is the first time levels and patterns of physical activity have been assessed at population level, using objective methodology. Even though the absolute values between the instruments used differed, they both provided qualitatively consistent pictures. This thesis has shown a new and sobering picture of health-enhancing physical activity at population level. At the same time, the need to better understand the nature and measurement issues of health-enhancing physical activity has been highlighted