Which age-related change contributes to decreased aerobic capacity?

• A. Lower red blood cell volume
• B. Higher red blood cell volume
• C. Increased VO2 max
• D. Increased lung capacity

Answer: (A)

Aerobic capacity falls with age largely because the blood’s ability to carry oxygen decreases, limiting the amount of oxygen that can reach working muscles during effort. This comes from a reduction in red blood cell volume, which lowers the amount of hemoglobin available to bind and transport oxygen. With less oxygen carried in each liter of blood, the muscles receive less oxygen during exercise, so VO2 max drops and endurance declines.

In other words, oxygen delivery is constrained by how much red blood cell mass (and thus hemoglobin) is present; reducing that mass directly lowers oxygen content of the blood and limits aerobic performance.

Choosing a higher red blood cell volume would improve oxygen transport, not diminish it; increasing VO2 max is itself the desired outcome, not a decline; and lung capacity typically does not increase with age, so those options don’t align with the aging pattern.