Your Heart on Exercise

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Presented by: Euan Ashley, MD, PhD
Assistant Professor, Cardiovascular Medicine
Stanford University Medical Center
August 14, 2009

Lecture Overview:

  • heartscanHeart rate is controlled by the internal nervous systems:  adrenaline speeds up the heart, while the vagus nerve slows it down
  • Benefits of exercise are numerous, ranging from increased stamina to improved balance and cognition to lowered cholesterol, blood pressure, and risk of heart attack.
  • When exercising, try to keep your heart rate up for at least 30-40 minutes three to five times per week.
  • The differences in an athlete’s heart include slower resting rates, more muscle elasticity, a slightly enlarged chamber, and a slight increase in wall thickness.

The heart, the hardest-working muscle in the body, pumps out about 50 cc of blood at every heartbeat and has the ability to beat more than 3 billion times over a person’s lifetime. It’s the pump that pulses blood throughout the body, delivering oxygen and nutrients to tissue, removing waste, transporting immune-system cells, and regulating temperature.

“Think of the heart as a pump for your fuel supply,” said Euan Ashley, MD, PhD, an assistant professor of cardiovascular medicine and director of Stanford Hospital’s Hypertrophic Cardiomyopathy Center, at a peak Performance Lecture at the 2009 Senior Games. “It is the only organ to be in constant motion and, obviously to me, the most interesting organ in the body!”

A normal heartbeat is initiated by a small pulse of electric current-tiny rhythmic impulses that make the heart muscle contract-produced by cardiac pacemaker cells. Any cell in the heart can take on the pacemaker role, which is one reason the heart can continue to pump when damaged.

Exercise and the Heart
Your heart rate increases even before you actually start to exercise, as eons of evolution prepare your body for the stress and challenge of activity. Your heart responds to two interconnected aspects of the nervous system: The sympathetic system that releases adrenaline, the “fight or flight” hormone that speeds your heart rate and diverts blood from your internal organs, and the parasympathetic system, made up of the vagus nerve, which serves to slow the heart rate down. Withdrawal of the parasympathetic system, which takes care of “rest and digest” functions, is one of the first things to occur before exercise.

To receive the benefits of physical activity, it’s important to check the level at which your heart is working, said Dr. Ashley. For some people, a chest-style heart rate monitor is an excellent way to pace yourself and to acquire the greatest benefit from exercise.

Though many groups suggest you work out your ideal heart rate during exercise by starting with your maximal heart as calculated by 220 minus your age, Dr. Ashley said there is a wide variation in this figure. “Find your own maximal heart rate rather than following an equation,” he suggested. “The idea is to keep your heart rate at 50-60 of the difference between your resting rate and this maximal rate for 45 minutes or more. The more beats per minute, the greater the volume of blood being pumped.”

The Athlete’s Heart
At rest, the heart pumps about 50 ml of blood per stroke; in an untrained athlete, stroke volume can increase to 120 ml with exercise; stroke volume in endurance-trained athletes can reach as much as 200 ml or more. When you run, the heart rate increases. This combination of higher heart rate and higher stroke volume leads to a much greater cardiac output..

“The hallmark of an athlete’s heart is its elasticity. It can increase the volume per beat,” Dr. Ashley said. “It can change volume quite dramatically. It’s the key to performance.”

Dr. Ashley also emphasized the idea that in humans, heart rate is a predictor of longevity. However he mentioned that it is hard to compare species, citing the long-lived whale, whose heart beats about four times a minute, to a shrew, whose heart beats about 1,200 times a minute.

He also referred to the myth that athletes have bigger hearts. An athletes’ heart tends to be about 1 millimeter thicker than average-a very subtle difference. “Heart size does not change that much in an athlete, but extra beats are more common in athletes,” he said.

Benefits of Exercise
Dr. Ashley’s extensive list of the benefits of exercise ranged from cardiovascular improvements to neurological fitness. These include:

  • Increased longevity
  • Reduced risk of heart attack and stroke
  • Improved cholesterol levels
  • Lower blood pressure
  • Less stress
  • Improved mood
  • Better agility and balance
  • Enhanced cognitive function
  • Reduced back pain
  • Endurance
  • Retained bone density
  • Less risk for glaucoma, inflammation, and gallstones
  • Potential anticancer activity for colon, breast, and pancreatic cancers

The only paradox to exercise is a very slight increase in the risk of heart attacks or death from cardiac arrest during exercise. In young athletes, the most common underlying cause is known as hypertrophic cardiomyopathy. This rare genetic disease causes the heart muscle (myocardium) to become abnormally thick, making it harder for the heart to pump blood. Young athletes are now often screened for the disorder. For most people, exercise of moderate intensity for 30 to 40 minutes three or for times a week will provide almost-immediate heart benefits.

“There’s really no downside to exercise,” Dr. Ashley said. “The benefits start to kick in after just 10 minutes.”

About the Speaker
Euan Ashley, MD, PhD, is an assistant professor of cardiovascular medicine and director of the Stanford Hypertrophic Cardiomyopathy Center, a multidisciplinary program that coordinates care for people with heart muscle disease. He is also director of Stanford’s Cardiopulmonary Testing Laboratory. He has a particular interest in the care of athletes with cardiovascular disease and works closely with the Stanford Sports Medicine program. An exercise physiology graduate of the University of Glasgow, Dr. Ashley received his PhD in molecular cardiology from the University of Oxford and his MRCP in medicine from the Royal College of Physicians. He joined Stanford in 2003.

For More Information:

Stanford Health Library can do the searching for you. Send us your medical questions.

Stanford Hypertrophic Cardiomyopathy Center

Dr. Ashley’s Research Laboratory

2009 Summer National Senior Games

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