Abstract

Objective To assess developmental trends in physical activity and sedentary behaviour in British adolescents in relation to gender, ethnicity and socioeconomic status (SES).

Design Five year longitudinal study of a diverse cohort of students aged 11-12 years at baseline in 1999.

Setting 36 London schools sampled using a stratified random sampling procedure.

Participants 5863 students categorised as white, black or Asian, and stratified for SES using the Townsend Index.

Main outcome measures Number of days per week of vigorous activity leading to sweating and breathing hard. Hours of sedentary behaviour, including watching TV and video gaming. Data were analysed using multi-level, linear, mixed models.

Results There were marked reductions in physical activity and increases in sedentary behaviour between ages 11-12 and 15-16. Boys were more active than girls, and the decline in physical activity was greater in girls (46% reduction) than boys (23%). Asian students were less active than whites, and this was also true of black girls but not boys. Black students were more sedentary than white students. Levels of sedentary behaviour were greater in lower SES respondents. Most differences between ethnic and SES groups were present at age 11, and did not evolve over the teenage years.

Conclusions Physical activity declines and sedentary behaviours become more common during adolescence. There are ethnic and SES differences in physical activity and sedentary behaviour in British youth that anticipate adult variations in adiposity and cardiovascular disease risk. These are largely established by age 11-12, so reversing these patterns requires earlier intervention.