Which genetic factor contributes to high VO2 max values possessed by elite endurance athletes?

• A. A large cardiovascular capacity
• B. A high percentage of slow muscle fibers
• C. A small heart
• D. Low hemoglobin

Answer: (A)

VO2 max is set largely by how much oxygen the body can deliver to and use in the working muscles. The key limit is maximal cardiac output, which is heart rate times stroke volume. The size and capacity of the heart determine how much blood can be pumped per beat, especially at maximal effort. A larger cardiovascular capacity means a higher stroke volume and thus a higher cardiac output during intense exercise, allowing more oxygen to be delivered to muscles and used for energy. That’s why having a genetically larger, more capable heart—or a heart that can sustain a higher stroke volume—contributes to higher VO2 max values seen in elite endurance athletes.

While having more slow-twitch muscle fibers can improve endurance performance by favoring efficient, aerobic metabolism, VO2 max itself is about oxygen delivery capacity, not just muscle fiber composition. Conversely, a small heart would limit stroke volume and reduce VO2 max, and low hemoglobin would lower the oxygen carried in the blood, also lowering VO2 max.