Which of the following would NOT contribute to a higher VO2 max?

• A. Increased maximum cardiac output
• B. Increased a-vO2 difference
• C. Increased blood volume and haemoglobin
• D. Reduced blood volume

Answer: (D)

VO2 max depends on delivering oxygen to the working muscles and the muscles’ ability to use it. Two main players are how much blood the heart can pump (cardiac output) and how much oxygen is extracted from the blood by the muscles (arteriovenous O2 difference).

Increasing maximum cardiac output raises VO2 max because more blood—and thus more oxygen—can reach the muscles each minute. Increasing the arteriovenous O2 difference raises VO2 max because muscles extract more oxygen from the same amount of blood, improving utilization. Increasing blood volume and haemoglobin boosts the blood’s oxygen-carrying capacity and supports greater oxygen transport, which also raises VO2 max.

Reducing blood volume, however, lowers venous return to the heart, decreases stroke volume and thus cardiac output, and limits the amount of oxygen that can be delivered to the muscles. Therefore it would not contribute to a higher VO2 max.