If Exercise Is Medicine: Are You Underdosing or Overdosing?

There's a healthy "Goldilocks zone" between too much and too little exercise. 

Posted Feb 27, 2020

Andrey Burmakin/Shutterstock
Source: Andrey Burmakin/Shutterstock

Extreme amounts of high-intensity endurance exercise may increase the risk of heart issues for those who are out of shape or have preexisting (but undiagnosed) heart problems, according to a recent scientific statement (Franklin et al., 2020) published on February 26 in the American Heart Association's journal Circulation.

After reviewing over 300 different studies, the authors of this report conclude that the benefits of regular exercise and improving physical fitness far outweigh the risks for the vast majority of people.

However, there is a caveat. As the authors explain, "extreme endurance exercise—such as participation in marathons and triathlons for people who aren't accustomed to high-intensity exercise—can raise the risk of sudden cardiac arrest, atrial fibrillation (a heart rhythm disorder) or heart attacks."

Any activity that causes a rapid increase in heart rate and blood pressure (e.g., shoveling snow, sprinting to reach a drop shot on a tennis court, running to catch the bus, etc.) can significantly increase the amount of instantaneous strain put on your heart.

Slow and steady increases in moderate-to-vigorous physical activity (MVPA) intensity during each workout (and in daily life), along with a long-term strategy for improving cardiorespiratory fitness incrementally, are best for heart health.

You should always warm-up at a slow and easy pace for a few minutes before you start any type of vigorous aerobic exercise. Warm-ups allow your heart rate to rise gradually without shocking your cardio system. 

"It is important to start exercising—but go slow, even if you were an athlete in high school," first author Barry Franklin, who is the director of William Beaumont Hospital's cardiac rehabilitation program and exercise laboratories, said in a news release. Additionally, after finishing your workout, a cool-down period in which your heart rate gradually returns to normal should be part of your routine.

For anyone who is currently inactive or sedentary, the American Heart Association recommends visiting your doctor for a check-up before kick-starting an exercise regimen or engaging in strenuous physical activities. "In addition, people with known heart disease (such as a previous heart attack, bypass surgery or angioplasty) should get their doctor's approval prior to starting an exercise program," the AHA guidelines state.

Because there are so many studies that have identified a cause-and-effect relationship between increased physical activity levels resulting in a lower risk of heart disease, many people have a misconception that "more exercise is better."

It's time to debunk the "more is better" exercise myth; too much high-intensity aerobic activity is not necessarily better and too much exercise may actually be harmful to your heart.

“Exercise is medicine, and there is no question that moderate to vigorous physical activity is beneficial to overall cardiovascular health. However, like medicine, it is possible to underdose and overdose on exercise—more is not always better and can lead to cardiac events, particularly when performed by inactive, unfit, individuals with known or undiagnosed heart disease," Franklin said.

There Is a "Goldilocks Zone" or "Sweet Spot" Between Overdosing and Underdosing on Exercise

The latest scientific statement (2020) from the American Heart Association drives home the importance of identifying an individualized "Goldilocks zone" in which the duration, frequency, and intensity of exercise optimize an individual's well-being while minimizing his or her risk of having an exercise-related acute cardiovascular event. 

Like so many things in life where moderation is key, the Goldilocks zone for healthy amounts of cardiovascular exercise lies between two extremes. This meta-analysis shows that between the two extremes of being a sedentary couch potato or an obsessively-driven exercise fanatic, there's a sweet spot or "dose-response" of cardio training that's just right. 

"Recent studies have also shown that large exercise volumes and vigorous intensities are both associated with potential cardiac maladaptations, including accelerated coronary artery calcification, exercise-induced cardiac biomarker release, myocardial fibrosis, and atrial fibrillation," the authors write. "The relationship between these maladaptive responses and physical activity often forms a U- or reverse J-shaped dose-response curve."

Below are some bullet-points that the American Heart Association recommends for implementing a healthy physical activity program:

  • Warm-up before exercise by doing the planned activity—such as walking—at a slower pace to let your heart rate rise gradually.
  • Cool-down after you exercise by walking at a slow pace to let your heart rate return to normal.
  • If you are currently inactive or sedentary, start by walking slowly on a level surface for 6-8 weeks, progressing to walking up hills, jogging, or taking part in more vigorous activities.
  • Increase the amount of time spent on cardio incrementally from about five to 10 minutes and build up slowly to your desired time. 
  • Discontinue any incremental progression of exercise duration and intensity if you start to experience symptoms such as shortness of breath, lightheadedness, chest pain, or chest pressure.
  • Lower the intensity of your exercise when specific environmental conditions (e.g., high humidity or being at a high altitude) put more strain on the heart.
  • The risk of cardiac events increases at high altitudes but can be decreased by spending at least one day acclimating to the elevation before strenuous activity.
  • Always stop and seek medical evaluation if you experience any heart-related symptoms such as lightheadedness, shortness of breath, or chest pain/pressure while doing physical activity.

For most people, moderate amounts of exercise reduce the risk of atrial fibrillation (AFib), which is a common heart arrhythmia associated with an increased risk of stroke.

However, a growing body of evidence suggests that those who "underdose" on the recommended weekly Rx "dose" of exercise (150 minutes of MVPA) by sitting too much and those who "overdose" on exercise by engaging in too much high-intensity training (e.g., running 60-80 miles per week) both tend to be at a greater risk of AFib.

Blogger's note: I know from first-hand experience that exercise is medicine; it's also an addictive drug. As a retired ultra-endurance athlete and someone who broke a Guinness World Record by running six back-to-back marathons in 24 hours and won the Triple Ironman (7.2-mile swim, 336-mile bike, 78.6-mile run) three years in a row...I know the life-threatening perils of OD'ing on exercise.

Christopher Bergland
Source: Christopher Bergland

At the peak of my athletic career, I retired from extreme-distance endurance sports and competition because "overdosing" on exercise was causing significant damage to my heart. Hopefully, this new report from the American Heart Association will encourage today's aspiring endurance athletes to avoid the reckless mistakes I made by pushing myself (and my heart) too hard.

To read a free excerpt from The Athlete's Way that describes how my heart started to eat itself near the end of this record-breaking 153.76-mile run, click here

If you're an endurance athlete, please get regular check-ups to make sure you don't have any undiagnosed heart issues. Also, please use common sense (e.g., don't run, bike, or swim for 24+ hours nonstop!) and do your best to consciously reduce your risk of "exercise-related acute cardiovascular events and potential deleterious adaptations following long-term exercise training" by heeding the latest (2020) advice from the American Heart Association.


Barry A. Franklin, Paul D. Thompson, Salah S. Al-Zaiti, Christine M. Albert, Marie-France Hivert, Benjamin D. Levine, Felipe Lobelo, Kushal Madan, Anjail Z. Sharrief, and Thijs M.H. Eijsvogels on behalf of the American Heart Association Physical Activity Committee of the Council on Lifestyle and Cardiometabolic Health; Council on Cardiovascular and Stroke Nursing; Council on Clinical Cardiology; and Stroke Council. "Exercise-Related Acute Cardiovascular Events and Potential Deleterious Adaptations Following Long-Term Exercise Training: Placing the Risks Into Perspective–An Update: A Scientific Statement From the American Heart Association." Circulation (First published online ahead of print: February 26, 2020) DOI: 10.1161/CIR.0000000000000749