Endurance training of muscles results in a(n) _____.

• A. Increase in mitochondria volume
• B. Decrease in mitochondria volume
• C. No change in mitochondria volume
• D. Decrease in mitochondria enzymes

Answer: (A)

Endurance training increases the muscle's oxidative capacity by boosting mitochondrial volume and the content of oxidative enzymes. Regular aerobic work stimulates mitochondrial biogenesis, so there are more mitochondria within each muscle fiber and higher levels of enzymes needed for oxidative phosphorylation. This enhancement allows ATP to be produced more efficiently during prolonged activity, improving endurance and delaying fatigue. You’ll also see related adaptations like greater capillary density and more myoglobin, which help deliver and utilize oxygen more effectively. Decreases in mitochondria or their enzymes aren’t typical adaptations to endurance training, making the increase in mitochondrial volume the best answer.