**1.1 Definition of physical activity and exercise**

Physical activity is defined as any type of bodily movement produced by skeletal muscles which results in an increased metabolism above resting level (Caspersen, Powell, & Christenson, 1985). Exercise is the planned, structured and repeated physical activity performed with the aim to improve performance, fitness and/or health (Bouchard, Blair, & Haskell, 2007). The term physical activity includes occupational physical activity, transport physical activity, housework and leisure time physical activity, whereas exercise refers to leisure time physical activity. Physical activity therefore includes all the terms exercise, work out and sports. In this chapter, the terms physical activity and exercise will be used interchangeably.
