Pubertal development and sedentary behaviour during adolescence.

The objective of the current study was to investigate the relationships between changing pubertal status, body composition, body image, and time spent in sedentary behaviours during adolescence. A mixed-longitudinal design was used involving 119 students from school Years 6 (10.0 - 10.9 years of age), 8 (12.0 - 12.9 years) and 10 (14.0 - 14.9 years). Participants were assessed in three phases carried out at six-month intervals. Cross-sectional results from Phase 1 showed that time spent in sedentary behaviours was significantly greater in participants who had started puberty compared with those who were pre-pubertal, and in those who were late-/post-pubertal compared with those who were pre-/early-pubertal. Also, students in Year 10 spent significantly greater time in sedentary behaviours compared with those in Years 6 and 8. These differences disappeared after controlling for the amount of time spent sleeping except for the Year 10 boys. It was concluded that differences in sedentary behaviour during adolescence were not associated with differences in behavioural choice related to greater maturity per se but to a greater opportunity for such behaviours with more waking hours. Longitudinal analysis examined changes between Phases 1 and 3. Analysis of covariance showed that, for boys only, weekday sedentary behaviour increased by a significantly greater amount for participants who increased puberty compared with those who stayed at the same pubertal level. No differences were found between pubertal groups for either gender during the weekend. No significant correlations were found between changing body composition and changing body image for boys or girls or between the change in pubertal status and change in body composition or body image. Multiple regression analysis showed that a significant amount of the variance of the increase in weekday sedentary behaviour could be explained by increased pubertal status for boys and reduced physical attractiveness for girls. When considering increasing weekend sedentary behaviour an increase in percentage body fat explained a significant amount of the variance for girls. It was concluded that only a part of the a priori hypothesis, that changes in sedentary behaviour are associated with pubertal changes, was supported by this data and that any changes found were not associated with behavioural choices triggered by body compositional changes.