What is the main function of cardiac output?

The main function of cardiac output is to indicate the amount of blood pumped by the heart in one minute. This measurement is critical because it reflects the heart's efficiency in supplying oxygen and nutrients to the body while removing carbon dioxide and metabolic waste. Cardiac output is a vital sign of cardiovascular health and is essential for maintaining adequate blood flow to meet the metabolic demands of tissues during various levels of activity.

When considering the other choices, measuring muscle strength pertains to assessing physical power, evaluating fat metabolism relates to how the body uses energy stores, and assessing respiratory capacity focuses on lung function. None of these options relate directly to the heart's function of circulating blood, highlighting the unique role cardiac output plays in maintaining physiological balance in the body.