Exercise is thought to be an effective means to quick weight loss. However, few people have realistic exercise-induced weight loss expectations. Fewer understand how weight is "lost" and where the lost mass goes. Understanding that fat is "burned" with inhaled oxygen and most of the mass lost must be exhaled as carbon dioxide might help individuals create realistic weight loss expectations. The purpose of this laboratory activity is to 1) provide students with a basic understanding of the role of oxygen in fuel metabolism during physical activity and its relationship to energy expenditure and mechanical work, and 2) engage students with collection of their own data to determine a realistic timeframe for exercise-induced weight loss. In the prelaboratory, questions such as, "When you lose weight, where does it go?" are asked. A guided discussion helps students understand the basic biochemistry required for weight loss. For the activity, students complete walking or running exercise, recording the time and distance. The relationship of exercise to physics' concepts of mechanical work and energy utilization are discussed with the concept of "calorie burn" and its relationship to oxygen consumption. Students estimate oxygen consumed and calories burned during exercise using established metabolic equations. Finally, the amount of energy (i.e., calories) equivalent to 1 pound of fat is discussed. Students calculate how long he/she would have to exercise to burn 10 pounds (4.5 kg) of fat. A person of average size and fitness, needs 60+ h of exercise to burn 10 pounds of fat. Supplementary activities including a dramatic gummy bear oxidation and the use of a metabolic cart reinforces these concepts and validates the laboratory estimates.
Keywords: carbon dioxide; metabolism; oxygen consumption; physical activity; weight management.