Certified Personal Trainer (NSCA) Practice Exam 2025 – Complete Prep Guide

During prolonged, moderate-intensity exercise, the body primarily relies on fat as its energy source. This is due to several metabolic processes that favor fat oxidation during extended periods of activity, especially as glycogen stores become depleted.

As exercise intensity decreases, the demand for rapid energy decreases as well, allowing the body to utilize fat more effectively. This process is efficient because fats provide a high yield of energy per gram compared to carbohydrates. While carbohydrates are critical for higher intensity efforts and for initial fuel in the earlier stages of prolonged exercise, the transition to fat oxidation occurs as exercise continues and intensity is maintained at moderate levels.

While protein plays a role in energy metabolism, particularly during extended exercise or in situations of caloric deficit, it is not the primary source of energy during prolonged moderate-intensity activities. Vitamins, on the other hand, serve as co-factors in metabolic pathways and do not provide energy directly. Their importance lies in supporting various physiological functions, but they do not serve as a fuel source like carbohydrates and fats. Thus, during prolonged moderate-intensity exercise, fat emerges as the principal fuel source.