Final answer:
The physiological variable responsible for the large variation in VO2 max across the normal population is maximal stroke volume. Stroke volume plays a significant role in determining VO2 max because it influences cardiac output, especially during exercise when the body's demand for oxygen and nutrients increases.
Step-by-step explanation:
Physiological Variable Responsible for Variation in VO2 max
The physiological variable responsible for the large variation in VO2 max across the normal population is maximal stroke volume (SV). VO2 max, or maximal oxygen consumption, is an indicator of an individual's aerobic capacity and cardiovascular fitness. Cross-sectional studies investigating the components of cardiac output, which is the product of heart rate (HR) and stroke volume, indicate that stroke volume has a significant influence on VO2 max.
During exercise, cardiac output (CO) increases to meet the body's higher demand for oxygen and nutrients. In healthy individuals, CO can increase significantly with exercise, largely due to increases in both HR and SV. Specifically, as heart rate increases during exercise, the rate of blood returning to the heart also increases, which can cause an increase in SV due to stronger heart contractions.
As exercise intensity continues to rise, HR can increase further, but there's a limit to how much this can compensate for increases in SV. Ultimately, top cardiovascular performance, reflected in higher VO2 max values, depends heavily on the body's ability to increase SV. Factors influencing SV include the strength of the heart's contraction and the volume of blood returning to the heart. Thus, while HR, systolic blood pressure, and the arteriovenous O2 difference also play roles in cardiovascular function during exercise, it is the stroke volume that is chiefly responsible for the broad variation in VO2 max seen across individuals.