What keeps your heart rate low during exercise?

Aerobic fitness. The more aerobically fit you are, the lower your heart rate will be during exercise. This is because your heart is able to pump more blood with each beat, so it doesn't have to beat as fast to deliver the same amount of oxygen to your muscles.

Age. Heart rate typically decreases with age. This is because the heart becomes less elastic as we get older, so it can't pump as much blood with each beat.

Gender. Women typically have lower heart rates than men. This is because women's hearts are generally smaller and they have less muscle mass.

Body size. People with larger bodies typically have lower heart rates than people with smaller bodies. This is because larger bodies require more oxygen, so the heart has to beat faster to deliver the same amount of oxygen.

Altitude. Heart rate typically increases at higher altitudes. This is because the air is thinner at higher altitudes, so the heart has to pump more blood to deliver the same amount of oxygen.

Medications. Some medications, such as beta-blockers, can lower heart rate.

Dehydration. Dehydration can cause heart rate to increase. This is because the blood becomes thicker when you're dehydrated, so the heart has to pump harder to deliver the same amount of oxygen.