During a maximum effort exercise lasting no longer than 10 seconds, what is the primary energy source?

The primary energy source during maximum effort exercise lasting no longer than 10 seconds is stored ATP. During this brief duration, the body primarily relies on anaerobic pathways for immediate energy needs. Stored ATP is readily available in muscle cells and provides the quick burst of energy required for high-intensity activities such as sprinting or heavy lifting.

Once the stored ATP is depleted, the body will then begin to utilize other energy systems, such as creatine phosphate, to regenerate ATP. However, for activities constrained to an upper limit of about 10 seconds, the amount of energy demanded far exceeds what can be sustained by any other source at that moment. Therefore, the reliance is predominantly on the immediate availability of stored ATP to fuel muscle contractions during this peak effort.

In longer durations of activity, the contributions from other sources such as glycogen and creatine phosphate become more significant, but that is not applicable in this very brief timeframe.