Utilization of Substrates
Understanding the physiology of exercise and the utilization of substrates can lead to a better understanding of the athlete’s nutrient needs. During prolonged, high intensity exercise, the body’s main sources of fuel are fatty acids (fat), blood glucose (circulating carbohydrates) and muscle glycogen (stored carbohydrates). Fatty acids provide fuel for lower intensity exercise (65% VO2max or lower) and blood glucose and muscle glycogen are needed for energy production in higher intensity exercise (75% VO2max or higher). Because humans have an abundant amount of stored fat and a limited amount of muscle glycogen, there is an interest in determining strategies to improve fatty acid oxidation. This will preserve muscle glycogen and inevitably lead to enhanced endurance. However, the Academy of Nutrition and Dietetics recommends forgoing dietary manipulation in order to enhance fatty acid oxidation and instead achieving desired results through regular aerobic training(3).