Composition of weekly physical activity in adolescents by level of physical activity

Background Physical activity (PA) in adolescence is crucial for lifelong healthy lifestyle, and attention is needed to adolescents at health risk due to insufficient PA. This study investigates the composition of weekly PA in adolescents by PA level and provides a rationale for change in their lifestyles. Methods The research was conducted at 66 schools in Poland between 2009 and 2016, among 949 girls and 650 boys aged 15-18 years. We used pedometers to monitor weekly PA with data assessed using the Indares web app. The participants were split into three groups by mean daily step count (lower, < 9000; middle, 9000-12,999; and higher, >= 13,000 steps/day), as a reliable and non-expensive indicator of PA. Results We did not observe statistically significant differences in composition of 7-day PA between participants with varying levels of PA, regardless of their gender (F-(12,F-9558) = 0.60; p = 0.841; eta(2)(p) > 0.000). The smallest differences in daily step counts by PA level were found on Mondays and the biggest on Fridays and Saturdays, in boys and girls; the differences between average school and average weekend days were most pronounced in less active girls (1677 steps/day) and boys (1886 steps/day). During the school week, the highest proportion of less active girls met the 11,000 steps/day recommendation on Fridays (21.9%), statistically significantly less than on other school days (p < 0.001). Similarly, less active boys (22.2%) had significantly less activity on Fridays than on other school days, except for Mondays (p = 0.143) Analogous pattern was apparent also in more active adolescents. Conclusions Less active adolescents have comparable composition of weekly PA to the more active ones but they can hardly meet the generally accepted PA recommendations. Better understanding of weekly PA composition and rates of meeting PA recommendations by day of the week can lead to more efficient interventions improving lifestyles. The recommendation of 9000 steps/day most days of the week, thus, appears appropriate for less active adolescents, as a motivating achievable goal.