Author(s): INGVARSDOTTIR, T.H., ARNARDOTTIR, N., ROGNVALDSDOTTIR, V., STEFANSDOTTIR, R., JOHANNSSON, E., Institution: UNIVERSITY OF ICELAND, Country: ICELAND, Abstract-ID: 1616

INTRODUCTION:
Despite its confirmed benefits on physical and mental health, physical activity (PA) decreases markedly during adolescence [1]. Organized sports participation (OSP) is an important contributor to PA during this stage [2]. Studies on changes in objectively measured PA and OSP in late adolescence and what factors predict the change in PA and OSP during those years are lacking. The objectives of the study were (1) to study changes in objectively measured PA and OSP from age 15 to 17; (2) to study if body composition, cardiorespiratory fitness, screen time, or mental health factors at age 15 predict the change in PA or OSP from age 15 to 17; and (3) to determine if there were any sex differences in the change or predictors of change in PA or OSP from age 15 to 17.
METHODS:
PA was objectively measured using Actigraph GT3X+ accelerometers for one week at age 15 and again at age 17 (n=144, 91 girls). Results were represented as total activity counts per minute of waking wear time. OSP was measured using a questionnaire and defined as participating in sports with a sports club at least once a week. Changes in PA and OSP were assessed with paired samples t-test and chi-squared test, respectively. Mixed-effect linear regression and logistic regression models were used to examine potential predictors of change in PA and OSP, respectively.
RESULTS:
Relative change in PA was -17.6% and -21.6% on weekdays and -6.4% and 1.2% on weekends for girls and boys, respectively. There was no sex difference in PA on weekdays, however, girls had higher levels of PA than boys on weekends at both measurement points. OSP dropped from 58.9% and 77.4% at age 15 to 37.8% and 43.4% at age 17, for girls and boys, respectively. Higher lean mass was associated with an increase in PA between ages 15 and 17 (β=21.3, 95% CI: 7.8-34.8.0, p=0.002), and higher BMI and higher body fat percentage were associated with decreased likelihood of persisting vs. quitting OSP between ages 15 and 17 (BMI: OR=0.83, 95% CI: 0.71-0.98, p=0.027; body fat percentage: OR=0.87, 95% CI: 0.80-0.95, p=0.002).
CONCLUSION:
PA decreases considerably between ages 15 and 17, especially during weekdays, and OSP drops substantially for both sexes. Increased lean mass at age 15 may serve as a protective factor against the decline in PA between ages 15 and 17. Those with higher BMI and increased body fat percentage may need more encouragement to persist in OSP during late adolescence.
References:
1. Dumith SC, Gigante DP, Domingues MR, Kohl HW. Physical activity change during adolescence: a systematic review and a pooled analysis. Int J Epidemiol. 2011;40:685-698.
2. Khan KM, Thompson AM, Blair SN, et al. Sport and exercise as contributors to the health of nations. Lancet. 2012;380:59-64.