This lesson focuses on energy production in the body through the digestion of food. The scene is a group of three novice runners preparing to run a marathon. During a marathon, energy is produced through cellular respiration in order for the muscles to contract. Students will learn that muscles use the stored chemical energy of food, converting it to heat and kinetic energy. The source of this energy used to power working muscles is adenosine triphosphate (ATP) – the body’s biochemical way to store and transport energy. The concepts covered here involve the expenditure of energy from nutrition and cellular respiration, with a particular focus on the strenuous energy demands of marathon running. For the learning activities, students will design their own menu to prepare for the big race, with careful attention to prevent a “hitting the wall” situation – caused by depletion of a glycogen source in the body during extreme activity. They will also be challenged to explain the Glycemic Index (GI) and the use of energy during “carbo-loading.” As prequisites to this lesson, students need prior knowledge on respiration, ATP, nutrition and digestion. The lesson will take about 60 minutes to complete but teachers may want to divide it into two class sessions if the activities require more time.