Too Much of a Good Thing?

Aerobic exercise is a crucial part of a well-rounded fitness program. Both the American College of Sports Medicine and American Heart Association recommend at least 150 minutes of moderate-intensity exercise per week as part of a complete routine. Following this recommendation helps protect against cardiovascular disease and control risk factors such as high blood pressure and obesity.

Whether for fun, fitness or performance, endurance athletes often exceed these guidelines by substantial amounts. An Ironman athlete at the peak of training may complete six times that recommendation! If a little is good, more must be better, right? As endurance athletes, you may remember reading some scary articles a few years back telling you that too much endurance exercise may actually harm your heart. Mainstream sources like The New York Times or The Wall Street Journal referenced scientific findings. Even fitness-oriented publications such as Outside and Competitor ran warnings.

It seems like every few years, a new fitness or nutritional fad comes along. At times, it can be hard to separate credible from nonsense. The fact is that, while regular intensive exercise leads to improved health on the whole, it also carries potential for some cardiac risks. These risks can be broadly categorized into structural issues that affect the heart’s contractile properties or electrical issues in which nerve signals normally propagated in the heart are in some way disturbed.

By now, some of you may have experienced some minor palpitations with the fear that your favorite hobby could be killing you. If you’ve already dialed 911…hang on just a little longer. To help dispel fact from fiction, I’ve posed a few questions to actual doctors. One is Vision Quest’s own Dr. Calvin Brown, Professor of Medicine with Northwestern Medical School. The other isDr. Kevin Sprouse, team physician for the Cannondale-Garmin Pro Cycling Team, board-certified in Sports Medicine and Emergency Medicine.

1. I read that endurance exercise can actually be bad for my heart. How worried should I be about this?

Dr. Calvin Brown: In most cases, exercise is extremely beneficial, not only for the heart, but also other body systems. However, a scientific study compiling the results of six individual exercise studies noted that about 10% of individuals exercising regularly showed a change in one factor that could lead to increased risk of heart attack, such as cholesterol, blood sugar or insulin levels. At the same time, these people showing increase in one risk factor also showed improvement in all other risk factors. Other studies of ultra-distance, cross-country skiers and former Olympic athletes from Britain revealed evidence of scar tissue in the heart, but all were unaffected. The British former Olympians remained athletic into their 60s and 70s.

Dr. Kevin Sprouse: The evidence overwhelmingly supports exercise as a healthy lifestyle choice. That said, it does look as though there are potential risks involved with too much endurance exercise. I would not say that you need to be “worried” about this, but I do think you should be aware of it. Making smart choices with your training and your lifestyle will lessen your risk and ultimately improve your health.

2. Why are we just hearing about this now? Is it more common or just diagnosed more often?

CB: Part of the reason is advances in technology; MRI scans of hearts were unavailable even a few years ago. At this point, it is solely something discovered in the tests, there is no sign it is causing any decline in performance or function. Scientists do not know how often this occurs, how much exercise may cause it or who may or may not get these changes.

3. Is there anything I can do to prevent this from happening to me?

KS: There are some risk factors that you need to address preventively. Athletes with high blood pressure, diabetes and worrisome cholesterol, or those who are smokers or over-indulgers in alcohol, should work to control those variables. You also should not exercise when sick. Viruses that cause simple illnesses, like the common cold, can affect the heart muscle if you continue to train while sick.

Regarding your training, a prudent plan and periodization of your training load can be helpful. Ultimately, it appears that an athlete’s risk of atrial fibrillation (AF) is proportional to the cumulative time that an athlete spends training. Decreasing your training volume appears to decrease your risk of AF. This doesn’t mean that you have to give up competing in longer events, but you may want to have periods where you focus on intensity rather than duration. It is also crucial that you take time off to recover. This process of recovery occurs in microcycles (a day off each week), mesocycles (an easy week each month) and macrocycles (two to four weeks entirely off every year).

4. Is it still safe to train if I’ve been diagnosed with a cardiac irregularity?

CB: It’s possible for healthy people to present with heart conditions that may or may not affect risk or performance. In the case of some specific heart rhythm conditions such as atrial fibrillation or premature atrial contractions, exercise can still be very beneficial for your heart. Getting an OK from your doctor, building up gradually and checking your pulse if it feels abnormal are all strategies that can allow people with heart conditions to continue training.

KS: You should discuss this with your physician. With properly treated AF, you should be able to return to training. The risks will depend on your treatment plan though. For instance, if you are placed on a blood thinner, the danger in a traumatic bike crash becomes much greater!

5. What are the treatment options and potential side effects?

KS: Atrial fibrillation is generally treated using either medication or a procedure known as ablation. When medication is used, your doctor will prescribe a drug that will keep your heart rate in an appropriate range. This generally will slow your pulse. Patients on such a medical regimen may also be placed on a blood thinner to reduce the likelihood of having a stroke. Both types of medications can cause problems for active people. An endurance athlete wants to be able to increase his heart rate in response to a hard training effort. If that response is blunted by medication, his performance will suffer greatly. Because of these side effects [slowed heart rate response and risks of crashing on a blood thinner], an ablation can be a preferred treatment for an athlete. This is a procedure during which the problematic electrical pathways in the heart are “re-routed.” A successful ablation will often allow an athlete to return to training without any side effects.

6. I have some known cardiac issues, but speak with my doctor regularly and have an established management plan. How should I proceed with my training?

CB: The best advice for those who enjoy endurance training is to carry on as usual. But remember to listen to your body and seek a doctor if you experience any symptoms (no matter how insignificant they may seem).

Join me in thanking both of these doctors for their expert contributions and perspectives on this multi-faceted topic.

In summary, there are real risks that endurance training could precipitate cardiac conditions. However, it appears the total affected athletic population is still relatively small and, despite these risks, the benefits of aerobic training are significant. A well-planned training routine, incorporating appropriate build and rest cycles, can reduce cumulative strain on the body from lifelong rigorous training. Take this last point to heart: serious athletes are often very resistant to actual rest, looking at it with nearly as much disdain as a twenty-minute test. Most importantly, don’t count on your training to be an everlasting fountain of youth. Schedule a yearly check-up with a qualified physician, particularly as you get older. If you do experience any worrisome symptoms, follow up promptly with that physician. As long as you have the green light for training, train hard, but train smart!

Reference List

American College of Sports Medicine:

American Heart Association:


New York Times:


Wall Street Journal:

Contributor Biographies

Dr. Calvin R. Brown Jr., M.D. is Professor of Medicine in the Division of Rheumatology of The Feinberg School of Medicine of Northwestern University. He also serves as director of the rheumatology training program there. Dr. Brown is a member of a number of professional organizations, including the American College of Rheumatology, the American College of Physicians, and is past president of the Chicago Rheumatism Society. His research has been published in such journals as Arthritis and Rheumatism and The Journal of Rheumatology. He is author of several textbook chapters dealing with arthritis and allied conditions. His areas of focus include education in the rheumatic diseases, sports medicine and disability evaluation. Dr. Brown received his medical degree from Wayne State University. He completed his internship and residency at Northwestern Memorial Hospital. He also completed fellowships in rheumatology at the University of Michigan and in orthopaedics at Rush University Medical Center.

Dr. Kevin Sprouse, D.O. is board-certified in both Sports Medicine and Emergency Medicine. He works with athletes of all abilities, from novice to professional endurance athletes from around the world. In his practice, Provision Sports Medicine (, he offers individualized consultation and concierge medical services to active individuals who are intent on optimizing their health and performance. Additionally, Dr. Sprouse serves as team physician and sports science consultant to the Cannondale-Garmin Pro Cycling Team, traveling throughout the year to care for these professional cyclists as they compete around the world.