PDHPE

At -3 to -2 minutes the ventilation rate is steady. The body does not have a high demand for oxygen when it is at rest.
At -1 to 0 minutes there is a slight increase in ventilation. This is because the body has a psychological response (anticipation), which causes breathing to increase just prior to exercise beginning. It is not as a result of an increased demand for oxygen.
From 0 to 1 minutes there is a rapid rise in the rate of ventilation. The demand for oxygen in the body will increase as muscles begin to work. An increased ventilation rate and a higher heart rate are required to supply the working muscles with the oxygen they need.
From 4 to +1 minutes exercise finishes and the ventilation rate falls rapidly. The muscles have stopped working and now have less need for oxygen. The ventilation rate will fall to reflect this lower demand.
From +3 to +4 minutes the body is still recovering from exercise. Immediately after exercise the ventilation rate falls rapidly. At this point, i.e. from +3 to +4 minutes on the graph the ventilation rate falls more gradually. The body still has a high demand for oxygen to assist the recovering muscle in the removal of waste (carbon dioxide and lactic acid). Ventilation rates above the levels required at rest are needed to supply this oxygen.