Purpose:

To determine the extent that sedentary behaviour and measures of obesity track from childhood to adolescence.

Background:

Tracking of sedentary behaviour from childhood to adolescence has not been extensively studied, and few studies have tracked accelerometry derived sedentary behaviour (1). Using objectively acquired sedentary time at repeated time points is important since the reliability of self-reported sedentary behaviour is likely to vary with age. The study by Baggett et al. (1) found fair-to-moderate tracking of sedentary behaviour, from 12 to 14-years, in sample of girls (kappa=0.17). A second study regarding accelerometer derived sedentary time found that, from 6 to 9-years, there was moderate tracking (r=0.37-0.52) (2).

The use of DXA derived fat mass as a measure of obesity is highly advantageous over certain anthropometric measures of obesity, as adolescence is a period when lean mass is increasing in addition to fat mass (especially among males). The findings by Cheng et al. (3) found that the tracking of fat mass, from 11 to 18-years, was good (r=0.65); however, only Finnish girls (n=396) were included in the analysis.

Dependent Variable:

- Sedentary Behaviour (Tertiles)

- Obesity [Percentiles: 90th (obese), 80th (overweight) & 10th - 79th (normal)]

Indpendent Variables:

- Age (time)

Covariates:

- Maturation (Tanner)

- Parental occupation (SES)

- MVPA

Data Analysis:

- General Estimating Equations (GEE)

- Analyses will be conducted by gender (due to the different stages of maturation) and by SES (to determine the extent of tracking according to SES)

Target Journals:

MSSE

British Journal of Sports Medicine.