Active 4 Life Practice Test

During exercise the heart rate rises to meet the body’s higher demands for blood flow. As muscles work harder, they need more oxygen and produce more carbon dioxide and heat, so the body increases heart rate (and often also increases how much blood each beat ejects) to boost the overall blood flow, known as cardiac output. The faster heart rate helps deliver oxygen and nutrients to muscles and remove wastes more quickly, supporting sustained activity.

If the heart rate decreased or stayed the same, the muscles wouldn’t receive enough blood and oxygen to keep up with the workload. If it became erratic, the system would be unstable and performance would suffer. So the best description is that heart rate increases to meet the extra demands placed on the body.