During a maximal effort lasting 6-10 seconds, which energy system supplies most ATP, and what is the limiting factor?

During a maximal effort lasting 6-10 seconds, which energy system supplies most ATP, and what is the limiting factor?

• A. Glycolytic system; depletion of glycogen stores limits ATP.
• B. Phosphagen (ATP-PCr) system; depletion of phosphocreatine stores in the muscle.
• C. Oxidative system; insufficient oxygen delivery.
• D. Phosphagen system; accumulation of ATP hydrolysis byproducts limits energy production.

Answer: (B)

For a maximal effort in the 6–10 second range, the body relies mainly on the phosphagen (ATP-PCr) system because it can rapidly generate ATP without the need for oxygen. The limiting factor is the finite pool of phosphocreatine stored in muscle. Once those PCr stores are exhausted, the ability to rapidly produce ATP declines, causing power output to drop and fatigue to set in. Resynthesis of phosphocreatine occurs during rest or low-intensity periods, so this system dominates only for a very short duration. Glycolysis and the oxidative system contribute more as the duration extends beyond this window, but neither can match the immediate, high-rate ATP production of the phosphagen system in such a brief sprint. The idea that glycogen depletion or byproduct accumulation is the primary limiter here does not fit the rapid, maximal power scenario, where phosphocreatine depletion is the bottleneck.

For a maximal effort in the 6–10 second range, the body relies mainly on the phosphagen (ATP-PCr) system because it can rapidly generate ATP without the need for oxygen. The limiting factor is the finite pool of phosphocreatine stored in muscle. Once those PCr stores are exhausted, the ability to rapidly produce ATP declines, causing power output to drop and fatigue to set in. Resynthesis of phosphocreatine occurs during rest or low-intensity periods, so this system dominates only for a very short duration.

Glycolysis and the oxidative system contribute more as the duration extends beyond this window, but neither can match the immediate, high-rate ATP production of the phosphagen system in such a brief sprint. The idea that glycogen depletion or byproduct accumulation is the primary limiter here does not fit the rapid, maximal power scenario, where phosphocreatine depletion is the bottleneck.