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We assess the performance of the respiratory system by measuring how much air is inspired or expired each minute. This is called minute ventilation. To calculate minute ventilation, we also need to know about breathing rate and tidal volume.

Breathing rate (or frequency, f) is the number of breaths taken in one minute. The average resting breathing rate is approximately 12-15 breaths in a minute.

Tidal volume (TV) is the amount of air inspired or expired in a normal breath. The average resting tidal volume is approximately 500 ml.

Minute ventilation (VE) is the amount or volume of air inspired or expired in one minute and can be calculated by multiplying tidal volume (TV) by breathing rate (f). The average resting TV is 500 ml and the average resting f is 15, so the average resting VE is 7500 ml/min or approximately 7.5 litres per minute.

During sport and physical activity, TV, f and therefore VE, all increase to make more oxygen available for the working muscles.