Correct Response: C. When carbohydrate levels are depleted during exercise the body oxidizes fat, which is stored as triglycerides in fat cells, for energy. With regular aerobic training the body becomes more efficient in utilizing the stored fats. With regular aerobic training, the heart becomes stronger and more efficient and does not need to beat as frequently to meet circulatory needs, hence there is no increase in maximum heartbeats per minute (A). Lung structure is not altered with training (B). Muscle-fiber composition is largely genetically determined (D), and studies indicate that potential changes in percentages of fast-twitch and slow-twitch fibers as a result of training are modest.
