The subjects run along the 20m shuttle track and back at constant speed until exhaustion

The starting speed is high, but at the end of each minute there is a triple beep which signals a slight decrease in pace

If  the subject runs faster than necessary (as indicated by the beeps) they will score higher predicted VO2 max. 

The starting speed is slow, but at the end of each minute there is a triple beep which signals an increase in pace by 0.5Km/hour