Energy for any work
Muscles cannot use food directly as fuel. Energy from carbs, fats, or protein must be converted into a usable form for muscle cells—ATP.
ATP is the universal currency
ATP directly powers muscle contraction, but stored ATP is tiny—only seconds at max effort—so the body must constantly resynthesize it.
Main fuel sources
- carbohydrates (fast energy, glycogen)
- fats (large reserve, slower)
- proteins (mainly building blocks; used as fuel in deficits)
All fuels overlap
The body uses multiple fuels simultaneously; the dominant one shifts with intensity and duration.
BALANS in practice
Different fuels. One currency: ATP.