Objectively measured physical activity in the 1993 Pelotas (Brazil) birth cohort

Data on physical activity levels of adolescents are mostly derived from self-reported instruments, and the vast majority of studies using objective measures are from high-income countries. The aim of this study was to describe the patterns of objectively measured physical activity in Brazilian adolescents.

In 2004-2005 (mean age of 13.3 yr), a subsample of the 1993 Pelotas (Brazil) Birth Cohort with data on all previous visits was approached. Physical activity was measured using the ActiGraph GT1M accelerometer (ActiGraph Corporation, Pensacola, FL). Demographic and other variables were assessed by self-report.

A total of 486 individuals (51% boys) provided valid data on objectively measured physical activity (response rate = 95.1%). The mean registered time of accelerometer data was 1191 min·d (SD = 112). The mean times (in minutes) spent in sedentary, light, moderate, and vigorous activities were 962 (SD = 114), 176 (SD = 46), 36 (SD = 16), and 17 (SD = 10) min·d, respectively. More than 30% of the adolescents accumulated ≥60 min·d of moderate-to-vigorous physical activity (MVPA). Physical activity intensity (counts per minute) and the prevalence of accumulation ≥60 min·d of MVPA were higher among boys and in those who walked or cycled to school. The prevalence of accumulation >60 min·d of MVPA was 125% higher in those from lower economic levels compared with higher economic levels (P < 0.001).

A large proportion of Brazilian adolescents of the 1993 Pelotas Birth Cohort do not achieve the current recommendation for health-related physical activity, and active commuting to school may be a target for interventions aimed at increasing physical activity. Physical activity levels are higher in lower socioeconomic groups than that in higher groups.