Lower ADP concentration following endurance training results in a ________.

• A. Lower reliance on glycolysis
• B. Higher reliance on glycolysis
• C. Increased glycolytic enzyme activity
• D. Increased lactate production

Answer: (A)

The main idea is how energy production shifts with endurance training. Endurance training boosts oxidative capacity—more mitochondria, greater oxidative enzyme activity, and better fat oxidation—so at the same submaximal workload, ATP is produced more efficiently by oxidative phosphorylation rather than relying on glycolysis. Because ADP is a key signal that stimulates glycolysis and ATP production, keeping ATP demand met with oxidative processes means ADP concentration stays lower. With less ADP stimulation, glycolytic flux decreases, so there is lower reliance on glycolysis.

This also helps explain why endurance-trained individuals have a higher lactate threshold and less lactate production at submaximal efforts. The other options imply more glycolysis or more lactate, which isn’t the typical consequence of the training adaptations described.