Changes in time-segment specific physical activity between ages 10 and 14 years: A longitudinal observational study

Objectives: Describe (1) time-segment specific changes in physical activity (PA) into adolescence, (2) differences in change in PA between specific time-segments (weekdays-weekends, in-school-out-of-school, out-of-school-weekends, lesson-time-lunch-time), and (3) associations of change in time-segment specific with overall PA. Design: Longitudinal observational study (4-year follow-up). Methods: Children from the SPEEDY study (n = 769, 42% boys) had PA measured by accelerometer for at least three days at ages 10.2 +/- 0.3, 11.2 +/- 0.3 and 14.3 +/- 0.3 years. Changes in moderate-to-vigorous PA (Delta MVPA, minutes >= 2000 counts/minute [cpm]) and total PA (Delta TPA, average cpm) during weekdays, weekends, in-school, out-of-school, lesson-times and lunch-times, were tested using three level (age, individual, school) mixed-effects linear regression. Differences in Delta MVPA/Delta TPA between time-segments were tested using time-segment x age interaction terms. Associations of four-year time-segment specific Delta MVPA/Delta TPA with four-year overall Delta MVPA/Delta TPA were tested using two level (time-segment specific Delta MVPA/Delta TPA, school) mixed-effects linear regression. Results: MVPA and TPA declined in all time-segments, except lesson-time MVPA. Annual Delta MVPA and, for boys only, Delta TPA was greater on weekends than weekdays (beta SE for interaction term: boys, -3.53 +/- 0.83 min, -29.64 +/- 7.64 cpm; girls, -2.20 +/- 0.64 min) and out-of-school (boys, -4.36 +/- 0.79 min, -19.36 +/- 8.46 cpm; girls, -2.44 +/- 0.63 min). Delta MVPA and Delta TPA during lunch-time was greater than during lesson-time (boys, -0.96 +/- 0.20 min, -36.43 +/- 6.55 cpm; girls, -0.90 +/- 0.13 min, -38.72 +/- 4.40 cpm). Delta TPA was greater out-of-school than in-school (boys, -19.89 +/- 6.71 cpm; girls, -18.46 +/- 6.51 cpm). For all time-segments, four-year Delta MVPA/Delta TPA was positively associated with four-year overall Delta MVPA/Delta TPA (all p < 0.042), except for girl's in-school and lunch-time TPA. Conclusions: Interventions focused on PA maintenance could target all time-segments, but weekends and out-of-school may be particularly advantageous due to the relatively large declines observed. (C) 2014 Sports Medicine Australia. Published by Elsevier Ltd.