The heart beats faster during exercise because the body needs more oxygen-rich blood during activity or excitement, according to the Cleveland Clinic. Exercise typically causes the heart to beat to more than 100 beats per minute.
The increase in heart rate mainly depends on the body’s need for oxygen-rich blood, says the Cleveland Clinic. The heart normally beats around 50 to 99 times per minute at rest, while heart rate rises to well over 100 beats per minute due to exercise, emotions, fever and certain medications.
David Freeman explains on WebMD that regular aerobic exercise makes a person’s heart stronger and more efficient, allowing the heart to pump more blood every time it contracts. The heart needs fewer beats per minute to perform its job. Athletic training can lower the normal heart rate by 10 to 20 beats per minute.
During exercise, the main job of the heart is to deliver more blood to the muscles, states Dr. Craig Freudenrich on HowStuffWorks. The heart’s blood flow rises by around four or five times from that of its resting state by increasing the heart rate and amount of blood that enters through the heart and goes to the rest of the body. The heart rate increases three times the normal rate when the sympathetic nerves stimulate the heart to beat faster as a person begins to exercise.