Which nutrient is the body’s main energy source during prolonged endurance activities?

• A. Proteins
• B. Fats
• C. Carbohydrates
• D. Vitamins

Answer: (C)

During long-endurance activity, the body needs a steady, readily available fuel. Carbohydrates fit this role best because they’re quickly broken down into glucose to fuel muscle contractions and ATP production. Stored as glycogen in muscles and the liver, these reserves are tapped continually during extended effort to sustain performance. Fats also supply energy, but they’re slower to mobilize and require more oxygen, so they become more important later as glycogen stores run down. Proteins aren’t used as a primary energy source in endurance work, and vitamins don’t provide calories themselves. So carbohydrates are the main energy source for prolonged endurance activities.