AIM: This study investigated objectively measured physical activity and sedentary time by sex, age and socioeconomic status in a large representative sample of Swedish adolescents.

METHODS: In this cross-sectional national survey between 2016 and 2017, students aged 11-12, 14-15 and 17-18 years from 131 schools were invited to participate. Physical activity and sedentary time were measured objectively with accelerometers for seven consecutive days. Socioeconomic status (parental education) and country of birth were self-reported in a questionnaire. Weight and height were measured by trained staff.

RESULTS: A total of 3477 adolescents participated in the study, and 2419 (73%) had at least 3 days of valid accelerometer data. The results showed that 43% of boys and 23% of girls reached the recommendation of 60 minutes of daily moderate-to-vigorous physical activity. Boys were more physically active than girls in all age groups. Girls with high socioeconomic status were more physically active than girls with low socioeconomic status (P < .001), and this difference was not found in boys.

CONCLUSION: The majority of Swedish adolescents did not reach the physical activity recommendation, and boys were more active than girls. Effective strategies to increase physical activity, especially among girls with low socioeconomic status, are urgently needed.