There are essentially 2 varieties of energy systems that the body utilizes, Aerobic and Anaerobic. every energy system produces nucleotide (ATP), that is used by the muscles to contract.
There are 2 varieties of muscle fibers, quick twitch (FT) and slow twitch (ST). quick twitch fibers are used for explosive sort movements and they are simply exhausted. Slow twitch muscle fibers contain a lot of mitochondria than quick twitch. Mitochondria are cell structures that contain specific enzymes, that are needed by the cell so as to use chemical element for energy production.