During physical exercise, what are the primary sources of energy for our bodies?

The primary sources of energy for our bodies during physical exercise are carbohydrates and fats. Carbohydrates are often the first source of energy used during exercise, especially during high-intensity activities. They are stored in the muscles and liver as glycogen, which can be rapidly converted to glucose and used to meet immediate energy needs.

Fats serve as a significant energy source during lower intensity and longer duration exercises. They provide more energy per gram than carbohydrates, making them essential for sustained physical activity once glycogen stores begin to deplete. The body can efficiently oxidize fat under aerobic conditions, providing a steady energy supply.

While proteins can be used as an energy source, they are primarily utilized for muscle repair and growth rather than as a primary fuel during exercise. The specific mention of glucose and oxygen emphasizes the role of aerobic metabolism, which relies heavily on carbohydrates and fats, making the combination of carbohydrates and fats the most representative answer for primary energy sources during physical activity.