Heart rate is the body’s speedometer. When you are working hard your heart rate is high; when you are at rest your heart rate is lower. Resting heart rate can be used to monitor changes in cardiovascular fitness. Specifically, a decrease in resting heart rate after you have done regular aerobic exercise for a few weeks is an indication of improved cardiovascular fitness. You may be wondering how that happens. The answer is simple: Aerobic exercise strengthens the heart muscle. A stronger heart muscle is able to pump more oxygenated blood to the body with each beat. A stronger heart can beat fewer times per minute than a weaker heart to supply the same amount of oxygen to the body. Heart rate is also used to determine how to exercise the body aerobically (see lesson 7.2).
