At rest, the heart of an athlete beats 72 times in a minute with a stroke volume of 70 mL…

Contributed by StemPy Lab

Try it on paper first. A hint, the key idea and the worked solution are here when you need them.

At rest, the heart of an athlete beats $72$ times in a minute with a stroke volume of $70\ \text{mL}$ . During a race, the rate rises to $150$ beats in a minute and the stroke volume to $100\ \text{mL}$ .

What is the cardiac output in the race, in litres in a minute?

How many times larger is it than the output at rest?

How long does the heart need in the race to pump $60\ \text{L}$ ?

Need a reminder? The key ideaShow

Muscular tissue is made of long cells called fibres that contract and shorten. Skeletal muscle is attached to bones, and its fibres are striated, long, cylindrical, unbranched and multinucleate. It is voluntary. Smooth muscle lies in the walls of internal organs such as blood vessels, the stomach and the intestine. Its cells are spindle shaped with one nucleus and no stripes. It is involuntary. Cardiac muscle forms the wall of the heart. Its cells are striated and branched, and they are joined end to end by intercalated discs with gap junctions, so that they contract as a unit. It is involuntary. The output of the heart is the rate times the stroke volume.

The worked solution

Have you tried it?

Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.

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