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.
Walaupun sel otot menggunakan ATP saat mereka berkontraksi berulang kali, mereka selalu membuat lagi, sehingga sering kali bahkan otot yang sangat kelelahan tetap tidak kehabisan sumber tenaga ini.