Replacing sedentary time with physical activity: strategies to improve markers of health across the lifespan

Abstract

Breaking up sedentary time has increasingly become an important target area for interventions aimed at improving markers of health. Many studies use various frequencies, intensities, times and types of activity to break up sitting with physical activity. However, the optimal configurations of physical activity breaks to improve markers of health across the lifespan is unclear. Many studies have assessed the effects of intermittent breaks in apparently healthy children, adults, and older adults, but fewer have assessed the response to interventions where a single bout of continuous physical activity is used to break up a sitting day. Therefore, the overall aim of this thesis is to determine the effects of continuous physical activity breaks used to break up sedentary time - in different aged populations - on markers of health. Chapter 2 examines the responses to the Daily Mile intervention which was anecdotally reported to have several physiological benefits including increased physical activity, reduced sedentary behaviour, increased fitness and improved body composition. It determined that the Daily Mile intervention is effective at increasing levels of moderate-to-vigorous intensity physical activity (MVPA), reducing sedentary time, increasing physical fitness and improving body composition in primary school children. Chapter 3 moves onto the adult population. Using an RCT design, it primarily examined the cardiometabolic responses to two energy matched bouts of physical activity (consisting of light-intensity physical activity (LPA) and moderate-intensity physical activity (MPA)) and a control in a sedentary inactive adult population. It primarily determined that interstitial glucose was higher during the MPA condition than during the sitting (SIT) condition, whereas an energy-matched LPA bout was not different to SIT. Chapter 4 builds on Chapter 3, utilising an RCT to explore the same LPA intensity, but focusses on determining whether a dose-response exists when comparing different lengths of LPA intensity in health inactive adults. It also secondarily explores whether responses differ depending on whether participants are in older or younger age groups. It determined that 60 minutes of LPA walking is sufficient to lower interstitial glucose in sedentary and inactive adults compared to sitting, with longer duration LPA lowering glucose to a greater extent than shorter duration LPA. It also determined that older adults did not respond to an LPA intervention in the same way as their younger counterparts. Overall, this thesis contributes novel data to the field of breaking up sedentary behaviour by examining physical activity strategies to improve markers of health across the lifespan. It identifies that continuous physical activity breaks have the potential to influence markers of health in children and adults and that older adults may not respond in the same way as their younger counterparts.