What change is developed by aerobic training?

• A. Increase in capillary density
• B. Increase in size of type 2 fibers
• C. Decrease in myoglobin content
• D. Reduction in mitochondrial density

Answer: (A)

Endurance adaptations from aerobic training focus on improving oxygen delivery and utilization in the muscle. The most characteristic change is an increase in capillary density, which expands the network that delivers blood and oxygen to each muscle fiber, reduces the distance oxygen must diffuse, and enhances the removal of metabolic byproducts during prolonged activity. This supports sustained aerobic energy production and improves endurance. In contrast, increasing the size of fast-twitch type II fibers is not a typical aerobic adaptation and is more related to strength or power training. Mitochondrial density and myoglobin content actually rise with aerobic training to boost oxidative capacity, so a reduction in mitochondrial density would hinder aerobic performance.