Abstract
ObjectivesDescribe (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.DesignLongitudinal observational study (4-year follow-up).MethodsChildren 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 (ΔMVPA, minutes ≥2000 counts/minute [cpm]) and total PA (ΔTPA, 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 ΔMVPA/ΔTPA between time-segments were tested using time-segment × age interaction terms. Associations of four-year time-segment specific ΔMVPA/ΔTPA with four-year overall ΔMVPA/ΔTPA were tested using two level (time-segment specific ΔMVPA/ΔTPA, school) mixed-effects linear regression.ResultsMVPA and TPA declined in all time-segments, except lesson-time MVPA. Annual ΔMVPA and, for boys only, ΔTPA 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). ΔMVPA and ΔTPA 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). ΔTPA 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 ΔMVPA/ΔTPA was positively associated with four-year overall ΔMVPA/ΔTPA (all p < 0.042), except for girl's in-school and lunch-time TPA.ConclusionsInterventions 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.
Highlights
Physical activity (PA) is important for young people’s health,[1] activity levels are often low and are reported to decline from childhood to adolescence.[2,3] Interventions focused on maintaining PA in youth may help confront the public health challenges associated with insufficient activity
Children included in the main analytical sample (n = 769) and the sample used to examine four-year change in activity (n = 279) had similar baseline personal, anthropometric, demographic and PA characteristics to those who were not included (n = 1295 or n = 1785)
moderate-to-vigorous intensity PA (MVPA) and total PA (TPA) declined with age for boys and girls in all timesegments, except MVPA during lesson-time (Table 1)
Summary
Physical activity (PA) is important for young people’s health,[1] activity levels are often low and are reported to decline from childhood to adolescence.[2,3] Interventions focused on maintaining PA in youth may help confront the public health challenges associated with insufficient activity. Psychological and environmental factors which influence PA helps inform intervention design.[6] Some studies suggest that these factors vary within- and between-days.[7,8,9] Investigating PA accumulated over specific times of the day or week is vital. In interventions aimed at PA maintenance there may be greater possibility to influence behaviour in the time-segments with the greatest decline
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