IB SEHS: Cardiovascular Responses to Exercise

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Stroke volume increases, then may plateau

Stroke volume is the volume of blood ejected per beat. From rest to moderate exercise, SV usually increases because venous return rises (more blood returns to the heart), ventricular filling improves, and contractions become stronger. In many untrained individuals, SV can plateau at higher intensities, meaning further increases in cardiac output depend mostly on HR.

If you want a clean, exam-friendly explanation with typical values and phrasing, review: 2.2.6 Notes: HR, SV, and cardiac output.

Cardiac output: the equation that makes your paragraph coherent

Cardiac output (Q/CO) is the total volume of blood pumped per minute. In IB SEHS, this is where students often lose marks by describing HR and SV separately but never connecting them. Do the opposite: connect early.

Use the line that markers love because it shows control:

As exercise intensity increases, HR increases and SV increases (then may plateau), so cardiac output increases (Q = HR × SV), delivering more oxygen to working muscles.

To build confidence analysing graphs and population differences, use: 2.2.7 Notes: analysing HR, SV, and CO data.

Blood flow redistribution: “priority shipping” for oxygen

Another key IB SEHS cardiovascular response to exercise is redistribution of blood flow. When exercise starts, arterioles supplying active muscles dilate, increasing perfusion where oxygen demand is highest. At the same time, blood flow to less immediately essential regions is reduced, improving efficiency and supporting sustained performance.

This fits neatly with broader transport content in the syllabus: A.1.3 Transport notes and the specific cardiovascular system overview: A.1.3.1 The cardiovascular system and bodily functions.

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Final takeaway for IB SEHS students

Cardiovascular responses to exercise are not random spikes; they are a coordinated plan: HR rises, SV rises (often then plateaus), Q increases, and blood flow is redistributed to where it matters. If you can write that chain clearly, you can answer most IB SEHS physiology questions with calm precision. When you are ready to practise under pressure, head to RevisionDojo for SEHS Study Notes, Flashcards, and the Questionbank that turns understanding into marks: A.1.3 Transport Questionbank.

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