Too much exercise is dangerous

Recent research has uncovered the dangers of competiive marathon running.  25 men who had completed 25 consecutive marathons over as many years were compared against 25 men sedentary men of the same age.

These gentlemen underwent 64 slice CT angiography of their coronary arteries and were compared to 25 sedentary men of the same age.  Surprisingly, the running group averaged 274 square millimeters of life threatening athersclerotic plaque vs. a mere 169 square millimeters for the guys who preferred to sit around.

This is suprising, if not downright alarming!  That’s because marathon runners do not appear to be at risk of heart disease.  A marathon race constitutes a kind of informal stress test, which these guys all passed repeatedly with flying colors.  High mileage runners typically have excellent Framingham scores, a standard measure of heart disease risk.  Runners also typically have excellent cholesterol levels, low resting heart rates and low body fat.


All of these outwardly visible favorable aspects of good health can be misleading.  So what’s going on here?  Marathon runners spend long hours of training under metabolically demanding conditions.  The stress of training has adverse effects on the inner lining of blood vessels that promote the formation of potentially lethal athersclerotic plaque.  Training entails a fast heart rate, high blood pressure, lactic acidosis and oxidative stress, or the release of high levels of tissue damaging oxygen radicals, the natural consequence of energy production inside the cells.


This study confirms similar research done in Germany and Greece.  In a German study, 108 marathoners were found to have significantly higher coronary calcium scores than non-marathoners of the same age.  A coronary calcium score is a CAT scan method for evaluating plaque build-up in coronary arteries.  Over a period of 21 months, 4 of the marathoners experienced new onset chest pain or heart attacks vs. none of the non-marathoners.

In the Greek study, 49 marathoners with an average age of 39, including 7 women, were found to have stiffer coronary arteries than non-marathoners of the same age and gender.  Stiffness is a measure of arterial health — increased stiffness suggests a history of chronic metabolic and mechanical insult.

It is important to note that in all of these studies, more superficial measures of cardiac risk such as risk scores, body weight, resting heart rate and cholesterol testing did not uncover the underlying damage caused by what appears to be excessive exercise.  One might also hypothesize that marathoners fail to allow sufficient recovery time between training sessions.   Could some marathoners be eating inadequate diets, without enough protein and natural fat.  Indeed, many marathoners exhibit an upper body muscle wasting consistent with inadequate dietary protein.  Also, running is a high impact exercise that can take its toll on weight bearing joints such as hips and knees, leading to painful arthritis.  Furthermore, there is interesting research that shows that most running shoes are poorly designed for human use and lead to increased risk of injury.


There is abundant research that shows the value of moderate exercise in preventing heart disease, dementia, depression and prolonging life.  This applies to both resistance training  and aerobic activities such as walking, cycling, rowing and dancing.  It appears that competitive marathoning may be too much of a good thing for some folks — even life threatening!

From an article in Internal Medicine News, June 1, 2010

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