From what sources does energy for physical activity mainly come?

The primary sources of energy for physical activity come from carbohydrates, fats, and to a lesser extent, proteins. Carbohydrates are the body's preferred fuel source, especially during high-intensity exercise, as they can be quickly converted to glucose for immediate use. Fats serve as a significant energy source during prolonged, lower-intensity activities, providing a more sustained energy release. While proteins can contribute to energy needs, particularly in endurance activities or when carbohydrate stores are depleted, they are not the primary source and are mainly utilized for muscle repair and growth rather than as a go-to energy source.

The other options do not accurately represent the comprehensive energy sources used during physical activity. Oxygen and hydration are crucial for energy production and overall performance but are not energy sources themselves. Limiting energy sources solely to carbohydrates or proteins overlooks the essential role that fats play in energy metabolism, particularly in varying types of physical activities. Thus, carbohydrates, fats, and proteins together create a balanced understanding of energy requirements for physical activity.