As you begin to read this blog post, consider how long you have been sitting for. When was the last time you got up to talk to a colleague or use the washroom? It’s now commonly understood that sedentary lifestyles tethered to desks and chairs do not align with our evolutionary history and do not preserve our health. We are advised to take breaks—stand, stretch, and go for walks—but does the type of activity break matter?
Researchers from the Baker Heart and Diabetes Institute in Australia published a new study in Applied Physiology, Nutrition, and Metabolism exploring how different intensities of physical activity affect how well our bodies metabolise glucose. The data suggested that the more intense of an activity break taken, the lower blood glucose levels drop. Lead author Dr. Robyn Larsen discussed the paper with us and the most effective ways to break up prolonged sitting.
Careers that require extended sitting have existed for some time. When did we start noticing significant impacts of sitting on human health and what changed to elicit these effects?
Research on sedentary behaviour can be traced back to mid-last century when early observations suggested a link between occupational sitting and cardiovascular disease. The seminal work of Morris and authors (1953) observed British civil servants and found higher rates of coronary heart disease and death among sedentary bus drivers and office workers when compared to their more physically active colleagues: bus conductors, who walk around collecting ticket fares, and postmen. Over recent decades, studies suggest that occupational sitting time has increased in many workplace contexts, including classically defined “blue” (non-office) collar occupations. Increasing use of information technology devices (e.g., computers, tablets, mobile phones) and labour-saving devices and more time spent in vehicles are thought to have contributed to increases in sitting time in both domestic and occupational environments.
What do measurements of glucose and insulin responses after a meal tell us?
Sustained high plasma glucose and insulin levels may be related, at least in part, to the pathogenesis of type 2 diabetes and subsequent cardiovascular disease. Consequently, there is much interest in exploring ways to reduce blood glucose and insulin concentrations over the course of the day. In our study, participants’ blood glucose and insulin responses to prolonged sitting were compared with sitting that was broken up with frequent short breaks of standing, light-intensity walking, or moderate-intensity walking. We characterised the lowering of blood glucose and blood insulin levels after different types of breaks in sitting and explored dose-dependent relationships. Our findings suggest that the increasing energy expenditure associated with the type of break in sitting improves blood glucose and insulin levels in a dose-dependent manner.
Your paper proposes that the intensity of the activity break affects glucose metabolism. How might duration and frequency of activity breaks affect metabolism?
We have yet to fully understand the mechanisms that link energy expenditure of the break in sitting and glucose metabolism. Our study will provide a basis for considering other potential intervention strategies such as alterations in break duration and/or frequency. As sitting is associated with low muscular activity, it is thought that the beneficial metabolic effects of breaks may relate to energy expenditure associated with muscle contraction. Even standing elicits thigh muscle activity, which is 2.5 times greater than that measured during sitting. Muscle activity increases blood flow, and beneficially alters the expression of genes in skeletal muscle that are linked to glucose metabolism. Therefore, it would seem probable that relative increments in energy expenditure from increased duration and/or frequency of activity breaks across the day would contribute to improvements in glucose metabolism. This is supported by other research that has shown that higher rates of energy expenditure from “daily activities” are associated with improvements in blood glucose and other risk markers for diabetes.
The studies you analyzed in your paper had participants walking on treadmills. What kinds of activities would you recommend for people to do in a work environment to achieve similar metabolic benefits to standardized exercises?
Substituting sitting with moderate-vigorous physical activity or light-intensity physical activity can increase energy expenditure. However, the practicality of undertaking normal work tasks may be limited while performing moderate–vigorous physical activity. Within occupational environments, task substitution to increase energy expenditure is more likely to be feasible with light-intensity activities. This type of light activity is more sustainable over the working day. Light intensity physical activities include standing, casual walking, and gentle exercises (such as leg lifts and calf raises). Regularly changing from a seated to a standing position also creates brief movements and postural variety, which may help to counteract the negative impacts of sitting on blood glucose metabolism, and reduce musculoskeletal discomfort which some people experience with extended periods of sitting.
Does timing of food consumption influence the metabolic benefits of activity breaks?
For the most part, our research has focused on the effects of breaking up sitting on postprandial (after a meal) blood glucose levels only over 1–3 days. So far, it appears that breaks in sitting attenuate blood glucose levels following breakfast, lunch, and the evening meal in individuals with or at-risk of type 2 diabetes. We have not yet examined the impact of breaking up sitting in a fasted state (>4 hours since last meal). However, given that up to three-quarters of the waking day is spent in a postprandial state, especially in Western societies, examination of the effect of breaking up sitting perhaps carries greater relevance to the postprandial state as it more closely resembles the real-life scenario for the majority of individuals.
The participants in the studies were overweight/obese adults, what other demographics benefit from activity breaks?
Individuals with, or who may be at risk of, type 2 diabetes may serve to benefit from regular activity breaks in sitting. Overweight and obesity is a risk factor for type 2 diabetes, but other risk factors include: having prediabetes (impaired glucose tolerance, impaired fasting glucose), having a parent or sibling with diabetes, having previously been diagnosed with gestational diabetes, having high blood pressure, having a low HDL cholesterol or high triglyceride levels, and/or having an ethnic background that may increase genetic susceptibility.
How do you and your colleagues ensure this type of research is communicated to health practitioners and the public?
This research fits within a program of sedentary behaviour research currently being conducted at the Baker Heart and Diabetes Institute. Publications from our research group have received wide media attention both nationally and internationally. Our work reporting on the detrimental association of sedentary behaviour with premature mortality and cardio-metabolic biomarkers has contributed to government and organisational guidelines and position stands on the likely importance of reducing sedentary behaviour in the community. These recommendations acknowledge that reducing sitting time should be done in addition to the current recommendations for increasing levels of participation in moderate–vigorous physical activity. We also have engaged with relevant stakeholders (industry partners) and give community talks to help to inform the public on the potential negative health implications of too much sitting.
What other obesity and nutrition research are you leading at the Baker Institute?
Utilising existing models on the experimental manipulation of sitting time and specialised technologies to assess sedentary behaviour and physical activity patterns, we are currently undertaking a program of research that is examining the influence of sitting time on the risk of developing gestational diabetes in pregnancy, and the effects of prolonged sitting on vascular function (the ability of the blood vessels to respond to stress).
