How the Heart Rate Response to Exercise Changes With Age

Your heart is the powerful pump that sends oxygen-rich blood to tissues when you exercise and at rest. Your heart speeds up during exercise to meet the demands of the hardworking muscles. After all, your muscles need oxygen to make ATP, the energy currency your body uses to fuel muscle contractions. Your body also requires oxygen at rest too, although at a lesser rate since your muscles aren’t working as hard.

As we age, subtle changes take place in the way our hearts pump blood and oxygen. These changes are most apparent during exercise. Typically, your resting heart rate doesn’t change much with age, although your resting heart rate will slow if you begin an aerobic training program. Why does aerobic training slow resting heart? Aerobic exercise makes your heart more efficient at pumping blood. As a result, it’s able to pump out more blood with each stroke so your heart doesn’t have to pump as many times per minute to deliver enough oxygen to muscles and tissues.

Some athletes develop an increase in the size of their left ventricle, the left lower chamber of the heart that pumps blood to the body. The wall may also become thickened. A thicker chamber can pump more blood to the body with each contraction. Why does this happen? It’s an adaptation your heart makes into aerobic exercise and is referred to as athletic heart syndrome. Although not dangerous, athletic heart syndrome can sometimes be mistaken for heart disease. The left ventricle also enlarges somewhat with age even if you don’t train aerobically. This is because the arteries become stiffer and less elastic. As a result, the left ventricle has to pump against greater resistance.

 Maximal Heart Rate Changes with Age

Although resting heart rate doesn’t change significantly with age, maximal heart rate does. Maximal heart rate is the fastest heart rate your heart can theoretically achieve during training. To get a rough estimate of your maximal heart rate, subtract your age from 220. For example, a 50-year-old person would have a maximal heart rate of about 170. Most experts now believe this formula isn’t that accurate but it does give a rough approximation for training purposes. You can use it to monitor the intensity of a workout.

As you can see from the formula, maximal heart rate goes down with age. Why does this happen? According to research from the University of Colorado School of Medicine, aging decreases spontaneous activity of the pacemaker cells, cells that initiate the heartbeat. These cells are located in the sinoatrial node, the pacemaker of the heart. As a result of this decreased activity, your heart doesn’t speed up as much during exercise or when you’re under stress. During exercise and stress, your adrenal glands release catecholamines that speed up the heart and increase the force of the heartbeat. With age, the heart seems to become less sensitive to catecholamines. This may be another factor that explains why maximal heart rate declines with age. The chambers of the heart also become stiffer and less elastic over time. This increases the amount of time they need to fill with blood. This also reduces maximal heart rate.

Stroke volume, the amount of blood your heart can eject with each beat, increases similarly in response to exercise in older people versus younger ones. On the other hand, stroke volume in the elderly may actually decrease during a maximal exercise effort. This leads to a reduction in aerobic power during high-intensity exercise.

The Power of Exercise

Here’s the good news. Aerobic training reduces some of the decline in aerobic fitness that occurs as a result of aging. In fact, according to the Encyclopedia of Sports Medicine and Science, aerobic training in seniors can “reduce biological age of the oxygen-transport system by 20 years.” One study showed endurance-trained Masters level athletes had about half the rate of decline in aerobic fitness as sedentary people of the same age.

Endurance training can increase aerobic power even in the elderly. One study showed the difference in aerobic capacity between an active versus sedentary senior corresponds to a biological age differential of about 15 years. Pretty impressive! Be inspired by people like Ed Whitlock of Canada, the oldest person to run a marathon in three hours at the age of 73.

Aerobic exercise also reduces risk factors for heart disease, the leading cause of death in the United States. It does this by reducing blood pressure and raising HDL, the good form of cholesterol that lowers the risk for heart disease. Exercise combined with good nutrition is one of the most important things you can do to keep your heart healthy as you age. It won’t stop the aging process but it can slow it down. Plus, it helps you stay functionally fit and reduce the risk of disability. It’s good preventive medicine.

References:

Eurekalert.org. “Why does maximum heart rate drop with age?”

Am J Geriatr Cardiol. 2007 Jul-Aug;16(4):222-8.

Encyclopedia of Sports Medicine and Science. “Aging and Exercise”

J Appl Physiol (1985). 1990 May;68(5):2195-9.

Circulation. 2003; 107: e2-e5. doi: 10.1161/?01.CIR.0000048890.59383.8D

The Journal of Physiology, 586, 55-63. January 1, 2008.

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