Sleep plays an important role in the health and well-being across the lifespan. However, the prevalence of sleep-related problems, such as poor sleep quality and short sleep is increasing. Poor sleep has been associated with various health disorders such as cardiovascular disease, metabolic syndrome and cognitive impairment. Regular moderate- and vigorous-intensity physical activity (PA) is considered as an important health protective factor. However, sedentary lifestyle is getting more prevalent in modern societies. A bi-directional relationship between sleep and PA has been reported. Increasing evidence indicates that regular exercise may improve sleep. However, little is known about how different sleep characteristics affect PA. The aim of this student project is to investigate the relationship between sleep and physical activity in Swedish middle aged and elderly women and men. We hypothesize that good sleep may be associated with higher physical activity or vice versa.