Final answer:
Carbohydrates become the primary fuel source at around 65-70% of VO2Max, with glucose and glycogen being utilized for high-intensity exercises. The percentage can vary based on diet and conditioning. Carbohydrate loading can help maximize muscle glycogen stores for endurance activities.
Step-by-step explanation:
Carbohydrates become the body's major fuel source at different percentages of VO2Max, depending on the intensity of the exercise and conditioning of the athlete. Generally, as exercise intensity increases to around 65-70% of VO2Max, the body's reliance on carbohydrates progressively increases. This is because, at higher intensities, the glycolytic pathway becomes more dominant for energy production, and glucose and glycogen stored in muscles are the preferred sources of fuel. During low to moderate intensity exercises (below 65% VO2Max), fats are predominantly used as the energy source.
The exact percentage at which carbohydrates become the major fuel source can also vary based on the individual's diet, metabolism, and the level of their aerobic and anaerobic conditioning. It is essential for athletes to consume a balanced diet with sufficient carbohydrates to replenish glycogen stores. A strategy such as carbohydrate loading can maximize energy reserves in the muscles, which is beneficial for endurance events.