Background: A large health survey was previously conducted in 1984-86, the Nord-Trøndelag Health Study (HUNT 1), and another was conducted in 1995-97 (HUNT 2). A third, HUNT 3, started in 2006. However, the physical activity (PA) questionnaires have not yet been validated.
Aims: To assess the reliability and validity of the self-reported physical activity questionnaire in the Nord-Trøndelag Health Study (HUNT 1).
Methods: The HUNT 1 questionnaire was administered to a random sample of 108 healthy men aged 20-39 years. Repeatability was assessed with a repeat questionnaire after one week, and validity by comparing results with direct measurement of VO(2) during maximal work on a treadmill, with ActiReg, an instrument that measures PA and energy expenditure (EE) and with the International Physical Activity Questionnaire (IPAQ). ActiReg records the main body positions (stand, sit, bent forward and lie) together with the motion of the trunk and/or one leg each second.
Results: The results indicated strong, significant agreement on test-retest (weighted kappa frequency, r=0.80, intensity, r=0.82, and duration, r=0.69). We found a moderate, significant correlation, r=0.48 (p< or =0.01), between the index based on questionnaire responses and VO(2max.) Metabolic equivalent (MET) values of 6 or more from ActiReg and "vigorous activity'' from the IPAQ most strongly correlated with the index (r=0.39, r=0.55, respectively). Associations of other measures obtained from ActiReg with questionnaire responses were weaker.
Conclusions: Our results indicate that the PA questionnaire in HUNT 1 is reproducible and provides a useful measure of leisure-time PA for men. The questionnaire is very short, and compared favourably with much longer instruments for assessment of more vigorous PA. It should be an appropriate tool for use in further epidemiological studies, particularly when the interest is in aspects of PA reflected in fitness or METs greater than 6.