title: Where does the time go? Patterns of physical activity in adolescent youth.
abstract: OBJECTIVE
  To explore daily patterns of physical activity in early adolescent youth, and identify whether patterns differed across varying activity levels.
  
  
  METHODS
  Cross-sectional observational study.
  
  
  METHODS
  Adolescent youth (n=715, 11.8-14.4 years) were asked to wear an Actigraph accelerometer for a 9-day period. Average daily and hourly minutes spent in moderate-vigorous physical activity (MVPA) were calculated for each participant. Participants were grouped into sex-specific quartiles (Q) based on average daily MVPA accumulation (Q4 most active, Q1 least active). Principal components analysis was used to identify, from hourly MVPA data, distinct time blocks for Weekday and Weekend days. Mixed between-within ANOVA's were conducted separately by gender to assess the impact of Quartile grouping on minutes of MVPA across the distinct time blocks.
  
  
  RESULTS
  Males accumulated significantly more minutes of MVPA daily than females (55.3±21.6min, versus 47.4±18.1min). Principal Components Analysis revealed three distinct time components for MVPA during weekdays, and weekend days. The total difference between Q4 and Q1 was greatest 'Weekend Afternoons' for Males (22min), and 'Weekend Midday' for females (12.8min); with Q4 accumulating significantly more MVPA in these time periods than the other three Quartiles (p<0.05).
  
  
  CONCLUSIONS
  This study points to the weekend midday and afternoon periods as particular time blocks to target for intervening with inactive youth. Future research should examine the reasons why some youth choose to be active during these particular periods while others do not, with a view to developing appropriate strategies for intervention.
authors.affiliation: The School of Health and Human Performance, Dublin City University, Ireland. Electronic address: sarahjane.belton@dcu.ie.
authors.forename: Sarahjane
authors.initials: S
authors.lastname: Belton
authors.affiliation: The School of Education, Sports Studies and Physical Education, University College Cork, Ireland.
authors.forename: Wesley
authors.initials: W
authors.lastname: O'Brien
authors.affiliation: The School of Health and Human Performance, Dublin City University, Ireland.
authors.forename: Johann
authors.initials: J
authors.lastname: Issartel
authors.affiliation: The School of Health and Human Performance, Dublin City University, Ireland.
authors.forename: Bronagh
authors.initials: B
authors.lastname: McGrane
authors.affiliation: The School of Health and Human Performance, Dublin City University, Ireland.
authors.forename: Danielle
authors.initials: D
authors.lastname: Powell
mesh_terms: D061725:Accelerometry / Q000379:methods*; D000293:Adolescent; D000294:Adolescent Behavior; D000704:Analysis of Variance; D016009:Chi-Square Distribution; D003430:Cross-Sectional Studies; D015444:Exercise; D005260:Female; D006801:Humans; D008297:Male; D025341:Principal Component Analysis; D012737:Sex Factors; D013997:Time Factors
keywords: Child; Health; Monitoring; Principal components analysis; Time period