The overall aim of the study is to characterize the development of the excessive exercise and to identify the genetic basis of this phenotype. Genetic regions have been selected on the basis of mouse genetic mapping studies revealing genetic loci for baseline physical activity levels. Specific aim 1: Validation of association between genetic candidate regions and physical activity levels. Hypothesis 1: There is a significant association between genetic variation in candidate regions and the self-reported as well as objectively measured participation in EE. Specific aim 2: Assessing the developmental trajectories of EE in females in childhood and adolescence and their relation to BMI. Hypothesis 2: Participation in EE is a phenotype developing during adolescence and associated with lowered BMI.