immediate energy system

im·me·di·ate en·er·gy sys·tem

(i-mē'dē-ăt en'ĕr-jē sis'tĕm) Intramuscular nonaerobic energy system composed of high-energy phosphates ATP-PCr; powers all-out physical effort for up to 6-8 seconds.
Synonym(s): high-energy phosphates.