ABSTRACT
This chapter outlines the energy systems required by the human body to fuel working organs, including the brain, heart, lungs and muscles. The major energy currency within the human body is an energy-rich molecule known as adenosine triphosphate (ATP). It requires continual resynthesis, which is supported by the three energy systems within the body: the phosphagen system (ATP-PCr, alactacid), anaerobic glycolysis (lactic acid) and oxidative phosphorylation (mitochondrial ATP production). While most physical activities require an energy contribution from at least two energy systems; all three systems are activated under maximal-effort conditions, with one energy system predominating at a given time. Following physical activity, oxidative pathways are the main contributor to replenishing energy stores and returning the body to its resting, dynamically balanced level of metabolism. Finally, there is an overview of estimating energy expenditure through measuring the body’s heat production or an individual’s oxygen consumption and carbon dioxide production for a given period has important implications for dietary intake and athletic performance.
