Medical researchers agree that exercising from the early years into old age helps to prevent heart attacks, strokes and cancers, but this month a study from The University of Manchester showed that long-term intense training for racing in animals can damage the atrial-ventricular node that regulates the frequency of heart beats to cause heart block (Circulation Research, 2021;129:e1–e20). “Heart block” means that the electrical signals that control your heartbeat are partially or completely blocked as they move from the top chambers of your heart (atria) to the bottom chambers (ventricles).

A training-induced heart block in human athletes is usually harmless and reversible when the athlete stops exercising (Dtsch Arztebl Int, Jan 7, 2013;110(1-2):14–24), but sometimes, such as when competing all-out in endurance sports, heart block is associated with increased risk for atrial fibrillation (J Am Coll Cardiol EP, Sept 2017;3(9):921–928). For example, an 80-year-old non-smoking, non-drinking life-long competitive marathon runner, with a resting heart rate of 40 beats per minute, fell while running and died from a blood clot thrown from his heart to his brain, caused by atrial fibrillation (Am J Case Rep, May 26, 2020;21:e924580). An irregular heartbeat induced by training and racing to an athlete’s limits can be detected by laboratory tests and in rare cases, may be an indication for the athlete to have an implanted heart pacemaker.

The Difference Between Racing and Just Exercising
Competing in endurance sports often requires exercising through pain and discomfort. Contracting skeletal muscles send large amounts of blood back to the heart, which stretches the heart muscle to cause it to beat faster and with greater force (Starling’s Law). When you are just exercising and feel some discomfort, you usually reduce the intensity of your workout to get back into your comfort zone. On the other hand, when you are competing in an endurance event, you try to push yourself through pain and discomfort, which can stretch the heart muscle fibers to near their limits.
• This stretching of the heart muscle can cause damage to the muscle filaments that increases stimulation of the vagus nerve that regulates heart rate, which can cause a slow heart rate (bradycardia) that can sometimes cause atrial fibrillation.
• Atrial fibrillation means that the atrium, the upper part of the heart, starts to flutter instead of contracting before the bottom part of the heart contracts. This allows blood to collect and stop moving in the upper part of the heart, which increases risk for forming clots that can pass to the brain to cause a stroke.

My Racing History
I had to work all through high school, college and medical school, so I never trained seriously for racing until I was in a fellowship at Johns Hopkins in 1963 at age 29. I worked up to running three times a day and competed seriously in races until 1974 at age 39. I trained so hard that I became an expert on running injuries because I had experienced many of them myself. Eventually I found that bicycling was much less likely to injure me, so from age 55 onward, I have tried to ride a bicycle seven days a week and now at age 86, average 150 miles each week. I have never raced on a bike, but I ride hard for about 30 miles on Tuesdays, Thursdays and Saturdays and around 15 miles very slowly on the other four recovery days.

This week I have been saddened by the deaths of two of my running contemporaries:
• Ron Hill, who died on May 23, 2021 at age 82 of dementia and an overwhelming urinary tract infection. He ran every day for 52 years and had a marathon best time of 2:09:28. In 1968, he set the world record for 10 miles twice (46:44.0); in 1969, he won the European marathon championship; in 1970, he set the Boston Marathon record (2:10:30) and won the Commonwealth Games marathon in a European, British, and Games record of 2:09:28 (Runners’ World, May 4, 2021).
• Dr. Joan Ullyot, who died on June 18, 2021 in Aspen, Colorado at age 80 of a heart attack. She was a pioneer in women’s long-distance running who did not run until she was 30 years old and ran her first marathon in 1974 at age 33. She won the master’s section of the Boston Marathon at age 43 (2:54:17), won 10 women’s marathons, and at age 48 ran the marathon in a women’s masters record 2:47:39. She also wrote and lectured extensively and had several best-selling books on women running in marathons (Runner’s World, June 23, 2021).

As You Age, Balance Intense Exercise with Common Sense
The American Heart Association cites more than 300 scientific articles showing that exercising excessively long and intensely may be associated with heart damage, increased plaque formation in arteries, scarring in the heart itself, markers of heart damage in the bloodstream, or atrial fibrillation (Circulation, Feb 26, 2020). However, a review of 48 articles found no reduction in lifespan, no matter how much a person exercises (Br J Sports Med, Aug 12, 2019).
Can Intense Exercise Increase Your Risk for a Heart Attack?
Vigorous Exercise Won’t Hurt a Healthy Heart

People who suddenly increase the length and intensity of their training may be at increased risk for heart attacks during exercise. This includes people who are starting a new exercise program, or regular exercisers who decide to enter an endurance event such as a marathon or triathlon so they suddenly increase the intensity and duration of their training (Circulation, Feb 26, 2020). CAUTION: Before increasing the intensity of your exercise program, check with your doctor to see if you have any pre-existing conditions such as heart arteries blocked by plaques, or heart or blood vessel abnormalities.

My Recommendations
I believe that with few exceptions, virtually everyone should try to exercise every day. Older athletes can continue to compete into their later years, but they need to remember that preventing heart problems involves more than just exercising. You can help to prevent heart attacks, cancers, dementia and premature death by following an anti-inflammatory lifestyle:
• Eat a plant-based diet that includes lots of fruits, vegetables, whole grains, nuts, beans and other seeds
• Avoid or severely restrict sugared drinks, sugar-added foods, red meat, processed meats and fried foods
• Lose excess weight if overweight
• Keep hydroxy vitamin D levels above 30 ng/mL
• And of course, exercise regularly