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Interrupting Prolonged Sitting Time: Implications for Type 2 Diabetes Management
In order to distinguish essays and pre-prints from academic theses, we have a separate category. These are often much longer text based documents than a paper.
In modern societies, most adults are exposed to environmental settings (at work, in automobile travel, and in the domestic environment) that can not only limit their physical activity, but also promote sitting for prolonged periods of time. Sedentary behaviours (put simply, too much sitting) have emerged as a health concern that is additional to a lack of moderate-to-vigorous physical activity (or ‘exercise’). Lifestyle interventions that include regular exercise are the recommended front-line therapy in the management of type 2 diabetes (T2D). However, despite the known benefits of meeting prescribed exercise guidelines – particularly for glucose metabolism, insulin sensitivity and blood pressure – doing so can be challenging, and many T2D patients remain physically inactive.
Recent epidemiological and experimental evidence indicates that interrupting prolonged periods of sitting can confer cardiometabolic benefit in healthy and overweight/obese populations. These findings may be of particular relevance to those with T2D – for whom glucose and blood pressure reductions (particularly in combination) are primary therapeutic goals – but whether the benefits extend to this clinical population remains unknown. Furthermore, experimental studies to date have only examined the acute effects of brief ambulatory and standing ‘breaks’ in sitting, whereas resistance-type exercises may confer additional or greater cardiometabolic benefits due to greater metabolic stimulus and practicality. This thesis provides initial experimental evidence of potential clinical relevance, demonstrating acute metabolic and cardiovascular effects of interrupting prolonged sitting time with brief bouts of ambulatory and resistance activities (half-squats, calf raises, brief gluteal contractions and knee raises) in 24 men and women with T2D.
An acute, 3-condition, randomised crossover trial in adults with diet/Metformin treated T2D was designed to determine, relative to a day of prolonged sitting (control), whether interrupting sitting with brief bouts of light-walking and simple resistance activities:
1) Attenuates postprandial cardiometabolic risk markers (Chapter 2)
2) Reduces resting blood pressure and sympathetic activity (Chapter 3)
3) Improves 22-h glucose homeostasis and nocturnal hyperglycaemia (Chapter 4)
Compared to prolonged sitting, interrupting prolonged sitting for 3 minutes every 30 minutes over 7 hours with either light-walking or simple resistance activities:
1) Attenuated concurrent postprandial circulating glucose, insulin and C-peptide concentrations. Postprandial triglyceride concentrations were lower for both activity conditions, however, this effect was only statistically significant for simple resistance activities. The magnitude of glucose reduction for the light-walking condition was significantly greater in women.
2) Reduced concurrent resting blood pressure levels and plasma norepinephrine concentrations, with the simple resistance activities having a significantly greater effect.
3) Showed carryover effects for glycaemic control (favouring the activity-breaks conditions) until the following morning – i.e. after participants vacated the controlled laboratory setting and returned to their free-living environments.
This thesis contributes a novel set of controlled experimental findings highlighting the potential for metabolic and cardiovascular benefits of interrupting prolonged sitting time with two different modes of activity break in T2D patients. It also presents new literature syntheses, interpretation and discussion on the relationships between physical activity, sedentary behaviour and cardiometabolic risk, with a particular focus on implications for T2D management. With the ubiquity of sedentary behaviours and the challenges for many of those with T2D of adhering to structured exercise, interrupting prolonged sitting has the potential to be beneficial and practical. However, the generalisability, longer-term efficacy and durability of these potential benefits, including a deeper understanding of the mechanisms that may underlie them, should be emphasised in future research.