Though muscle cells use up ATP as they  contract repeatedly, they are always making more, so most of the time even heavily fatigued muscles still  have not depleted this energy source.
Iako mišićne stanice iskoriste ATP kako se u više navrata kontrahiraju, uvijek stvaraju više, pa većinu vremena čak i jako umorni mišići još uvijek nisu potrošili ovaj izvor energije.