Insomnia Symptoms and Cardiorespiratory Fitness: the Hunt Study

99 Insomnia Symptoms and Cardiorespiratory Fitness—Strand et al INTRODUCTION Insomnia is a self-reported condition that includes difficulty falling asleep or remaining asleep.1,2 Insomnia is common in patients with cardiovascular disease and a growing body of evidence suggests that insomnia is associated with an increased risk of coronary heart disease,3-5 but the underlying mechanisms for this association are largely unknown. However, several studies have reported that people with insomnia symptoms tend to have a lower level of physical activity,6-9 which could represent a possible explanation for the increased risk of coronary heart disease in these individuals. Insomnia could also be inversely associated with cardiorespiratory fitness because its major determinant is physical activity. However, so far only two relatively small studies have assessed the association between sleep and cardiorespiratory fitness using exercise tests.10,11 Whereas physical activity corresponds to any bodily movement produced by skeletal muscles INSOMNIA SYMPTOMS AND CARDIORESPIRATORY FITNESS: THE HUNT STUDY