Too Much Exercise Not As Beneficial As Moderate Training

Date: Jun-08-2012Although regular moderate exercise improves longevity, cardiovascular health and is effective at preventing many common chronic diseases, extreme endurance exercise may lead to myocardial injury, say researchers.

The study, published in the June issue of Mayo Clinic Proceedings, found that training for, and competing in marathons, very long distance bicycle rides, and iron man distance triathlons, may result in structural changes to the heart and large arteries, leading to myocardial injury.

Micah True a 58 year-old legendary ultra-marathoner, would run as far as 100 miles in a day. However, on March 27, 2012, True died suddenly while on a routine 12-mile training run. Autopsy results showed that True's heart was enlarged and scarred and that he died of a lethal arrhythmia (irregular heart rhythm).

The researchers speculate that the pathologic changes in True's heart may have manifestations of ""Phidippides cardiomyopathy," a condition caused by chronic excessive endurance exercise."

Jame H. O'Keefe, M.D., of Saint Luke's Hospital of Kansas City, MO. explained:

"Physical exercise, though not a drug, possesses many traits of a powerful pharmacologic agent. A routine of daily physical activity can be highly effective for prevention and treatment of many diseases, including coronary heart disease, hypertension, heart failure, and obesity.

However, as with any pharmacologic agent, a safe upper dose limit potentially exists, beyond which the adverse effects of physical exercise, such as musculoskeletal trauma and cardiovascular stress, may outweigh its benefits."

According to Dr. O'Keefe and his team, extreme endurance training can result in transient structural cardiovascular changes, as well as elevations of cardiac biomarkers, all of which return to normal within one week.

However, some people may develop patchy myocardial fibrosis, particularly in the atria, interventricular septum, and right ventricle, and an increased susceptibility to atrial and ventricular arrhythmias, as a result of months and years of repetitive injury.

In one study, researchers found that apparently healthy marathon runners were significantly more likely to develop coronary heart disease during a two-year follow up than controls. In addition, the team found that around 12% of these runners showed evidence for patchy myocardial scarring.

Even though elite-level athletes commonly develop abnormal electrocardiograms and atrial and ventricular entropy, these conditions were not thought to influence serious arrhythmias or sudden cardiac death.

According to the researchers, it now appears that cardiac changes caused by excessive exercise can result in rhythm abnormalities. Studies have also found that individuals who participate in endurance sports, such a professional cycling or ultramarathon running are up to five times more likely to develop atrial fibrillation.

Furthermore, coronary artery calcification, large-artery wall stiffening, and diastolic dysfunction may also be linked to chronic excessive sustained exercise.

Although individuals who participate in vigorous exercises regularly have excellent functional capacity, and low mortality and disability rates, more research is needed in order to identify those who are at risk for adverse cardiovascular changes, and to create physical fitness regimens for conferring optimal cardiovascular health and longevity, said Dr. O'Keefe.

In a video interview Dr. O'Keefe states that the study does not detract from the importance of exercise.

He said:

"Physically active people are much healthier than their sedentary counterparts. Exercise is one of the most important things you need to do on a daily basis. But what this paper points out is that a lot of people do not understand that the lion's share of health benefits accrue at a relatively modest level. Extreme exercise is not really conducive to great cardiovascular health. Beyond 30-60 minutes per day, you reach a point of diminishing returns."

Written By Grace Rattue

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