Condition Heart rate (bpm) Stroke volume (ml) Cardiac output (l/min) Rest 72 70 5.04 Light exercise 110 90 9.90 Vigorous exercise 170 120 ? The table below ...

(a) The formula used to calculate cardiac output is:

Cardiac output = heart rate x stroke volume [1]

Cardiac output measures the total volume of blood pumped by the heart per minute, combining how fast the heart beats (heart rate) with how much blood is ejected per beat (stroke volume).

(b) Calculating cardiac output during vigorous exercise:

Cardiac output = heart rate x stroke volume [1]

= 170 bpm x 120 ml

= 20,400 ml/min, which equals 20.4 litres per minute. [1]

This is approximately four times the resting cardiac output (5.04 l/min), demonstrating the enormous increase in blood delivery the body requires during intense physical activity.

(c) Stroke volume increases during physical activity because:

• The heart muscle contracts more forcefully during exercise due to increased stimulation by the sympathetic nervous system and the release of adrenaline. [1]
• This stronger contraction means more blood is pushed out of the ventricles with each beat, increasing the volume of blood delivered to the working muscles per heartbeat. [1] Additionally, increased venous return (more blood flowing back to the heart from the working muscles) stretches the ventricles, triggering a stronger contraction through the Frank-Starling mechanism.