During exercise, your muscles should metabolise faster as they require both more oxygen and nutrients. This then makes the heart pump the blood harder and faster to keep up with the demand, as the heart is doing more work to supply the blood. This means that more oxygen is required, meaning, the response given is breathing being increased so that oxygen is pumped to all cells quicker. Due to homeostasis, levels of oxygen in the blood are always being measured, ensuring oxygen, carbon dioxide and pH levels return to their norm. Messages that are sent to the effectors informing them that the breathing rate has been increased, however, will decrease again when all activity has been stopped.
