| dc.description.abstract | Physical activity, and particularly moderate and vigorous physical activity, has a range of positive health effects throughout one’s life span. Establishing healthy physical activity habits during childhood is highly important because both physical activity and sedentary behaviors tracks from childhood into adolescence and adulthood. To promote physical activity and lower sedentariness, knowledge of health promoting factors is essential. Therefore, this thesis seeks to identify individual, familial and contextual predictors of moderate and vigorous physical activity in middle childhood (Study II). The main purpose of the two other studies included in this thesis is to explore how objectively measured physical activity affects two important aspects of mental and physical health, namely, symptoms of depression (Study I) and body fat (Study III). The three studies apply data from the Trondheim Early Secure Study. The participants were 4 years old when the first data collection was carried out in 2007/2008; however the measures of physical activity, sedentary behavior and body fat were assessed for the first time when the children were 6 years old. This thesis is thus based on data collected when the children were 6, 8, 10, 12 and 14 years. We found moderate and vigorous physical activity to protect against later symptoms of depression throughout middle childhood. There was no opposite relationship; symptoms of depression did not affect later physical activity. This study demonstrated the importance of moderate and vigorous physical activity for mental health in childhood, and therefore, the second study aimed to identify factors explaining why some children are more active than others. The results showed that only certain 6 individual child factors, such as spending time outdoors and being a boy were associated with more physical activity, whereas objectively measured sedentary behaviors were associated with less physical activity. Children who had access to gardens and living in traffic safe areas were also more active than those who did not. Surprisingly, parental factors did not affect children’s physical activity; parents’ own physical activity levels, whether the parents spent time outdoors with their child and how often parents transported their child to school had no significant impact on children’s physical activity. Finally, in the third study we found that boys who displayed increased body fat were less physically active and spent more time being sedentary than other children over time. Among girls however, body fat had no impact on their physical activity levels. Furthermore, we found that increased physical activity did not predict changes in later body fat in childhood. However, among boys, there was a relationship during the transition into adolescence; boys who were more physically active when they were 12 years old had lower levels of body fat than other children when they were 14 years old. This effect was also absent in girls. Taken together, this thesis illustrates how physical activity can protect against depressive symptoms but has less effect on the development of body fat in childhood. These findings suggest that parents and caregivers should promote physical activity, particularly moderate and vigorous physical activity, by facilitating outdoor activity in traffic safe areas. Boys with increased weight are at risk of becoming less physically active and more sedentary over time; hence, interventions facilitating physical activity among these boys are highly important. The gender differences revealed in our studies further suggest that measures to promote physical activity in children and adolescents should consider that boys and girls differ, thus, the predictors and outcomes of physical activity are not necessarily the same for boys and girls. | en_US |
