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Can Endurance Exercise Be Harmful?


 

In 490 BC, Pheidippides (or possibly Philippides) ran from Athens to Sparta to ask for military aid against the invading Persian army, then back to Athens, then off to the battlefield of Marathon, then back to Athens to announce the army’s victory, after which he promptly died. The story, if it is to be believed (there is some doubt among historians), raises an interesting question: Are some forms of exercise dangerous?

Running a marathon is a lot of work. The “worst parade ever,” as one spectator described it, is not without its risks. As a runner myself, I know that it doesn’t take much to generate a bloody sock at the end of a long run.

But when most people think about the risks of exercise, they mean the cardiovascular risks, such as sudden deaths during marathons, probably because of the aforementioned ancient Greek’s demise. The reality is more reassuring. An analysis of 10 years’ worth of data from US marathons and half-marathons found that out of 10.9 million runners, there were 59 cardiac arrests, an incidence rate of 0.54 per 100,000 participants. Others have found incidence rates in the same range. An analysis of the annual Marine Corps and Twin Cities marathons found a sudden death rate of 0.002%.

Marathon runners do sometimes require medical attention. In the Twin Cities cohort, 25 out of every 1000 finishers required medical attention, but 90% of their problems were mild. The majority included issues such as dehydration, vasovagal syncope, hyperthermia, and exhaustion. Musculoskeletal problems and skin abrasions made up the rest. Objectively, long distance running is fairly safe.

Running and Coronary Calcium

Then a study comes around suggesting that marathon runners have more coronary artery calcium (CAC). In 2008, German researchers compared 108 healthy male marathon runners over 50 years of age with Framingham risk–matched controls. The marathoners had a higher median CAC score (36 vs 12; P =.02), but scores across the board were quite low and not all studies were in agreement. The MESA study and another from Korea found an inverse relationship between physical activity and coronary calcium, but they compared sedentary people with vigorous exercisers, not specifically marathoners.

Two later studies, published in 2017, generally corroborated that endurance exercise was associated with higher calcium — with some caveats. A group from the Netherlands looked at lifelong exercise volume and compared men who accumulated > 2000 MET-min/week with those who exercised < 1000 MET-min/week. Again, the analysis was limited to men, and CAC scores, though statistically different, were still very low (9.4 vs 0; P =.02). Importantly, in men with coronary plaques, the more active group had less mixed plaque and more calcified plaque.

A UK study of middle-aged masters-level athletes at low cardiovascular risk had similar findings. Most of the study population (70%) were men, and 77% were runners (not all were marathoners). Overall, the male athletes had not only more plaque but more calcified plaque than their sedentary peers, even though most male athletes (60%) had a CAC score of zero.

The findings from these two studies were interpreted as reassuring. They confirmed that athletes are a generally low-risk group with low calcium scores, and although they might have more plaque and coronary calcium on average, it tends to be the more benign calcified type.

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