Background: High physical activity and cardiorespiratory fitness may protect from the development of cardiometabolic disease outcomes but the mechanisms involved are not fully understood. 

Aims: The aims of this study were to examine the associations of physical activity and cardiorespiratory fitness with traditional and novel cardiometabolic biomarkers, fatty liver and carotid artery elasticity and intima media thickness in a longitudinal population-based cohort study. 

Participants and methods: This thesis is part of the Cardiovascular Risk in Young Finns Study. In 1980, 3,596 children and adolescents aged 3-18 years participated in the study. Self-reported leisure time physical activity including commuting activity was assessed by a questionnaire and blood samples were analyzed in 1986, 2001, 2007 and 2011. Carotid artery ultrasounds were examined in 2001 and 2007. A cardiopulmonary exercise test was undertaken in 2008-2009 and liver ultrasounds were performed in 2011. 

Results: Physical activity and cardiorespiratory fitness were inversely associated with adiposity, heart rate, smoking, serum insulin, insulin resistance and Creactive protein levels in adults. Leisure-time physical activity in boys and young adults was associated with better carotid artery elasticity later in life. Cardiorespiratory fitness was inversely and independently related with the risk of fatty liver regardless of adiposity. 

Conclusions: Physical activity and cardiorespiratory fitness are favorably and independently associated with several cardiometabolic risk markers. These observations offer novel mechanistic insights into the beneficial effects of high physical activity and cardiorespiratory fitness on cardiometabolic disease outcomes.