ABSTRACT
Our current population’s health status and the prevalence of chronic conditions are a consequence of our lifestyle and altered nutritional habits. Governments and healthcare organisations all over the world have developed guidelines and interventions aimed at curbing the escalation in chronic ill health. These interventions and guidelines are underpinned primarily by physical activity and nutritional recommendations. One of the key arguments in this fight against chronic ill health is the relationship between energy intake and usage. This chapter will discuss the fundamental concepts of energy, adaptation and physical activity. One element to be considered is the human need for large amounts of energy and why this was important in our evolutionary trajectory. As such, this chapter will consider a more contemporary view of energy budgets and how these reconcile with health and fatigue.
