Describe how heart rate, stroke volume, and cardiac output respond to increasing rates of work. illustrate how these three variables are interrelated.

Increasing rates of work will increase the energy demand of the body. To fulfill the energy needs, the heart needs to pump more blood. 

The rate of blood pumped by heart is known as cardiac output while stroke volume is the amount of blood pumped each contraction. It is calculated by: heart rate x stroke volume

The easiest variable to changed to increase the cardiac output would be heart rate. When a person increases his rates of work, the heart rate will be increased to increases the cardiac output so the heart can supply the energy needed.

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