Which statement best describes the effect of endurance training on mitochondrial density and endurance performance?

Which statement best describes the effect of endurance training on mitochondrial density and endurance performance?

• A. Endurance training decreases mitochondrial density.
• B. Endurance training has no effect on mitochondria.
• C. Endurance training increases mitochondrial density, contributing to improved endurance performance.
• D. Endurance training increases mitochondrial density with only tiny gains in endurance.

Answer: (D)

Endurance training drives mitochondrial biogenesis in skeletal muscle, increasing the number of mitochondria within muscle fibers. This expansion of the mitochondrial network boosts the muscle’s oxidative capacity, meaning more ATP can be produced aerobically during prolonged activity. With more mitochondria, enzymes involved in aerobic metabolism and fatty acid oxidation ramp up, and capillary density often improves as well, supplying more oxygen and nutrients to the working muscles. The result is a clearer ability to sustain higher intensities for longer and to delay fatigue, which translates into better endurance performance.