Background: To validate the physical activity (PA) questionnaire in Nord-Trøndelag Health Study (HUNT 2).
Methods: The questionnaire was administered twice to a random sample of 108 men aged 20-39 and validity by comparing results with VO(2max) and ActiReg, measuring PA and energy expenditure and with the International Physical Activity Questionnaire (IPAQ).
Results: Spearman correlation coefficients indicated poor and moderate significant agreement by test-retest (light activity, r = 0.17, and hard activity, r = 0.50). We found a moderate significant correlation r = 0.46 (p < or = 0.01) between hard PA and VO(2max) and n.s for light activity (r = -03). Metabolic equivalent (METs) values 6+ from ActiReg most strongly correlated with hard PA r = 0.31 (p < or = 0.01), though associations of other measures obtained from ActiReg with questionnaire measures were weaker. Occupational activity was strongest correlated for METs 3-6 r = 0.48 (p < or = 0.01) by ActiReg.
Conclusions: The HUNT 2 question for "hard" LTPA has acceptable repeatability and appears to be a reasonably valid measure of vigorous activity, as reflected in moderate correlations with several other measures including VO(2max), and with corresponding results from IPAQ and ActiReg. The HUNT 2 question on occupational activity had good repeatability and appears to best reflect time spent in moderate activity, with moderate associations with measured time at intermediate intensity levels. The "light" activity question from HUNT 2 had poor reproducibility and did not correlate well with most of the comparison measures. Thus, the "hard" PA and the occupational activity question should be useful measures of vigorous PA, if time and space allow only very brief assessment. The utility of the "light" PA questions remains to be established.