Secular and longitudinal physical activity changes in population‐based samples of children and adolescents

Abstract

The aims of this study were to investigate whether physical activity (PA) and sedentary time (ST) in 9‐ and 15‐year‐olds differed between 2005‐2006 and 2011‐2012 (secular change), and to investigate changes in PA and ST from age 9 to 15 (longitudinal change). In 2005‐2006, we invited nationally representative samples of Norwegian 9‐ (n=1470) and 15‐year‐olds (n=1348) to participate. In 2011‐2012, we invited a new nationally representative sample of 9‐year‐olds (n=1945), whereas 15‐year‐olds (n=1759) were invited to participate either based on previous participation in 2005‐2006 or from a random sample of schools. We assessed PA and ST objectively using accelerometers. In 2011‐2012, both 9‐ and 15‐year‐olds spent more time sedentary (≥35.7 min/d, P<.001) and less time in light PA (≥35.2 min/d, P<.001) compared to their peers in 2005‐2006. Nine‐year‐old girls also spent less time in moderate‐to‐vigorous PA (MVPA) (4.2 min/d, P=.041). In both age groups, the proportion accumulating an average of 60 min/d of MVPA did not differ between the two cohorts. From age 9 to 15, girls and boys decreased their time spent in LPA (≥106.7 min/d, P<.001) and in MVPA (≥20.8 min/d, P<.001). During the same period, ST increased by a mean of >2 h/d (P<.011). We observed an adverse secular change in PA from 2005‐2006 to 2011‐2012 among 9‐ and 15‐year‐olds, and a large decline in PA in the participants followed longitudinally from age 9 to 15 years.