Fitness and Health in Older Adults: High Cardiorespiratory Fitness as a Mediator of the Cardiovascular Risk Associated with Sedentariness and Adiposity
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Cardiorespiratory fitness (CRF) is a strong and independent predictor of cardiovascular health, and currently the only known major risk factor for cardiovascular disease (CVD) that is not routinely assessed in clinical practice. Determination of reference values for CRF and consensus on clinically relevant cutoffs that associate with higher health risk for various populations are particularly lacking for older adults, who are typically underrepresented in large population studies. Sedentary behavior and adiposity are closely linked to adverse health outcomes and negatively affect the risk of CVD. The potentially mediating effect of CRF previously shown in younger populations, however, has not yet been adequately addressed in older adults. Given the anticipated increase in the number of older adults, improved understanding of the complex interplay of behavioral and cardio-metabolic risk factors for CVD will generate basic knowledge to implement effective, individualized intervention strategies for the older population. Therefore, the primary objectives of this thesis were to provide reference values for directly measured CRF and cardiorespiratory function in a large and diverse sample of older Norwegian women and men, and to investigate how high CRF modifies cardiovascular risk factors associated with sedentary behavior and adiposity. Study I presents directly measured CRF (VO2peak) and cardiorespiratory function in 1567 women and men aged 70-77 years, representing the currently largest reference data in an older population worldwide. Additionally, differences in physiological response to cardiopulmonary exercise testing between women and men, and subgroups of CVD patients and healthy individuals are discussed. In Papers II and III, we demonstrate a robust inverse association of high age-specific CRF and risk factors for CVD, independent of levels of sedentary time, physical activity, body mass index and body composition. Having high CRF attenuated the adverse association of prolonged sedentary time and the clustering of cardiovascular risk factors, even in participants not meeting the current recommendations for physical activity. Furthermore, we demonstrated that low CRF and adiposity cumulatively associate with higher likelihood of having an unfavorable cardiovascular risk factor profile. These findings emphasize the importance of including both CRF and measures of adiposity in the assessment of cardiovascular risk and health promotion efforts. In this context, CRF below 25.7 mL·kg-1·min-1 in women and 30.7 mL·kg-1·min-1 in men represented critical thresholds for unfavorable cardiovascular risk factor levels in older adults. The findings of this thesis provide novel information on CRF and cardiorespiratory function for researchers and clinicians to interpret data from cardiopulmonary exercise testing in older adults, and demonstrate the benefits of having high agespecific CRF on cardiovascular health.