Novel insights into the physical activity continuum and cardiometabolic health in adults

The primary aims of this thesis were: 1) to examine the associations between physical activity behaviours and indices of cardiometabolic health in older adults; and 2) to explore the theoretical effect on cardiometabolic health markers by reallocating time between sedentary time, standing time, light intensity physical activity (LIPA) and moderate-to-vigorous physical activity (MVPA) in older adults. Due to strong evidence in support of the use of activPAL monitors for accurately measuring sedentary time, standing time and postural changes, the activPAL3 Micro was chosen for this body of research. To classify physical activity of different intensities, the ability of the activPAL3 Micro to predict energy expenditure was explored, and subsequently deemed not to be accurate. A count-to-activity threshold for the activPAL3 Micro was subsequently developed and validated to provide accurate measures of time spent in different intensity bands. Habitual physical activity data and cardiometabolic health markers were collected from 323 participants of the Mitchelstown Cohort Rescreen Study. Sedentary time had detrimental associations with body mass, percentage body fat, HDL-C, VLDL-C, triglycerides and diastolic blood pressure. Increased LIPA and MVPA were beneficially associated with body mass, BMI, percentage body fat, VLDL-C, triglycerides and blood pressure (to varying magnitudes). Only VLDL-C and triglycerides were beneficially associated with standing. Theoretically replacing sedentary time (by 10 minutes) with LIPA resulted in significant decreases in body composition measures and blood pressure. Replacement with MVPA resulted in significantly lower triglyceride levels. No beneficial changes were observed when replacing sedentary time with standing. The results suggest that LIPA has an important role for maintaining, and improving, cardiometabolic health, in conjunction with MVPA. The findings from this thesis can be used to inform future interventional studies, while also contributing to the development of future public health guidelines on how best to reduce sedentary time.