Creatine monohydrate supplementation for 28 days has no significant effect on aerobic power, ventilatory threshold, lactate threshold, or time to exhaustion in healthy young men compared to placebo.

Creatine increases muscle phosphocreatine stores, but this only helps with short bursts of power. Aerobic endurance depends on oxygen use, mitochondrial energy production, and how efficiently the body clears lactate — none of these are changed by creatine. So even with more creatine, the body still hits the same limits when cycling or running for a long time.