Physical activity and physical inactivity in the aetiology of obesity

Overweight and obesity are associated with increased risks of many poor health outcomes, including cardiovascular disease, type 2 diabetes, arthritis, depression and some cancers [1].
Overweight and obesity arise in adults as a result of accumulative weight gain, which occurs when there is a positive energy balance – that is, when energy intake exceeds energy expenditure, resulting in energy storage. Conversely, weight maintenance
occurs when the body is in a state of energy balance, when energy intake and energy expenditure are balanced over a period of time, resulting in minimal energy storage [2]. Therefore, it can be hypothesised that energy expenditure is an important determinant of long‐term energy balance and, consequently,
weight change over time. Energy expenditure should be viewed as a continuum of behaviours, as energy is expended in all waking activities – including those performed lying and sitting down (commonly termed sedentary behaviours); light to moderate activities such as walking or household chores; and vigorous activities such as running or playing competitive sports.
The objective of this chapter is to describe the evidence for cross‐sectional and longitudinal associations between physical activity, physical fitness and sedentary behaviour with overweight and obesity in adults. Relationships between current physical activity guidelines and weight gain prevention are also discussed.