The current project includes three main studies. A first study tests the feasibility of the new ActivPal monitors and its relationship with accelerometers and it also evaluates the reliability and validity of questionnaires to measure sedentary behaviour and light-intensity activity in young children, adolescents, adults and older adults (n=100 in each age group). In the second study a series of determinant studies of sedentary behaviours and light-intensity behaviours will be executed in four different age groups (children, adolescents, adults and older adults; 500 participants each). In the third study, prospective relationships and interactions with personal, social and environmental

determinants will be determined, by 2 follow-up evaluations (one-year intervals).