Final answer:
Fast glycolytic fibers produce ATP via anaerobic glycolysis, allowing for quick and powerful contractions but leading to faster fatigue due to lower ATP yield per cycle.
Step-by-step explanation:
The threshold for fast glycolytic fibers, also referred to as Type IIb fibers or fast-twitch muscle fibers, relates to the point at which these muscle cells switch predominantly to anaerobic glycolysis to produce adenosine triphosphate (ATP), the energy currency of the cell. Fast glycolytic fibers are capable of producing high levels of tension and contracting quickly by utilizing ATP produced through glycolysis, which allows these fibers to generate powerful movements in a short amount of time. However, due to relying on anaerobic glycolysis for ATP production, these fibers yield less ATP per cycle compared to oxidative fibers and thus, fatigue much faster. Fast glycolytic fibers are prevalent in activities requiring short, explosive movements, such as sprinting or weightlifting.