Researchers revealed that regular moderate to intense physical activity between the ages of 11 and 13 was associated with better mental health.
Physical activity was also associated with reduced hyperactivity and behavioural problems, such as loss of temper, fighting with other children, lying, and stealing, in young people.
Researchers from the
The devices recorded levels of moderate physical activity - typically defined as brisk walking or cycling - as well as vigorous activity which boosts heart rate and breathing, such as aerobic dancing, jogging or swimming.
The young people and their parents reported on their levels of depressive symptoms from age 11 and at age 13 years. Participants' parents and teachers were also quizzed about the young people's general behaviour and emotional difficulties.
In analysing the impact of moderate to vigorous exercise on the young people's mental health and behaviour, the team also considered factors such as age, sex and socio-economic status.
They found that higher levels of moderate or intense physical activity had a small but detectable association with decreases in depressive symptoms and emotional difficulties.
Regular exercise had a small but detectable association with reduced behavioural problems, even after controlling for other possible influences, the study found.
The findings suggest regular moderate and intense physical activity may have a small protective influence on mental health in early adolescence, researchers say.
Researchers say the study is the first to offer such a comprehensive approach to examining mental health and exercise in young people.