Define requirement of energy for Physical activity?

This is the most variable and, after BMR, the second largest component of daily energy expenditure. Humans perform obligatory and discretionary physical activities. Obligatory activities can seldom be avoided within a given setting, and they are imposed on the individual by economic, cultural or societal demands. The term "occupational" was used earlier in the WHO/FAO/UNU 1985 report but the preferred term now is obligatory as it is more comprehensive.

In addition to occupational work, obligatory activities include daily activities such as going to school, attending to the home and family and other demands made on children and adults by their economic, social and cultural environment. Discretionary activities, although not socially or economically essential, are important for health, well-being and a good quality of life in general. They include the regular practice of physical activity for fitness and health, the performance of optional household tasks that may contribute lo family comfort and well-being; and the engagemen1 in individually and socially desirable activities for personal enjoyment, social interaction and community development. We will dwell further on this aspect later in this unit; however, we need to look at two concepts in the context of physical activity namely physical activity level (PAL) and physical activity ratio (PAR), which find extensive use in calculating the total energy requirement of healthy, well-nourished adults.