Which metabolic pathway is primarily active during the first 10 seconds of high-intensity exercise?

The phosphagen (ATP-PC) pathway is the primary energy system utilized during the initial burst of high-intensity exercise, particularly in the first 10 seconds. This pathway is designed for quick energy release and operates through the breakdown of creatine phosphate (CP) stored in the muscles to regenerate adenosine triphosphate (ATP), the main energy currency of the cell.

During high-intensity efforts, such as sprinting or heavy lifting, the demand for ATP spikes rapidly. The phosphagen system can provide this ATP almost instantaneously, which is critical in short-duration, high-power activities. The phosphagen pathway allows for maximal effort without delays associated with other energy systems that require additional metabolic processes.

As exercise continues beyond this initial phase, the body will begin to transition to the lactic acid pathway and eventually to the aerobic system for longer durations and lower intensity, but for the first 10 seconds, the reliance on the phosphagen system is paramount for sustaining maximum output.