Physical activity is defined as any bodily movement produced by skeletal that results in energy expenditure. The doubly labeled water method for measurement of total energy expenditure (TEE), in combination with expenditure, is the reference for physical activity under free-living To compare the physical activity level (PAL) within and between species, divided by resting energy expenditure resulting in a figure without The PAL for sustainable lifestyles ranges between a minimum of 1.1-1.2 maximum of 2.0-2.5. The average PAL increases from 1.4 at age 1 year to at reproductive age and declines again to 1.4 at age 90 year. Exercise increases PAL in young adults when energy balance is maintained by energy intake. Professional endurance athletes can reach PAL values Most of the variation in PAL between subjects can be ascribed to A higher weight implicates higher movement costs and less body movement necessarily a lower PAL. Changes in physical activity primarily affect composition and to a lesser extent body weight. Modern man has a similar wild mammal of a similar body size.