Looks like the mainstream media is finally turning with regard to extreme endurance events like marathons, triathlons, and distance training. Here, the UK Mail reports on the "hormetic" aspect of endurance exercises and training:
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.
We've known about the J-curve aspect of endurance training. Too much is harmful. But how much is too much? The safe upper limit or ceiling seems to be one hour:
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 ... 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 ...
We all agree with this. Plus the article points out that too much endurance training will elevate inflammation:
Dr O’Keefe and colleagues said research suggests that extreme endurance training can cause transient structural cardiovascular changes and elevations of cardiac biomarkers
But what we didn't know: too much training can lead to "the development of patchy scarring of certain areas of the heart, and abnormal heart rhythms."
In one study, approximately 12 per cent of apparently healthy marathon runners showed evidence for patchy myocardial scarring, and the coronary heart disease event rate during a two-year follow up was significantly higher in marathon runners than in runners not doing marathons .. [i]t had been known that elite-level athletes commonly develop abnormal electrocardiogram readings.
Really, when did we know this? The Paleo argument was that endurance training is dangerous for those with latent inflmmation (DeVany). Also, it could elevate cortisol, resulting in inflammation (Cordain). But structural changes to the heart and and arteries leading to rhythm anomalies?
Chronic excessive sustained exercise may ... be associated with other heart problems including artery wall stiffening. The phenomenon has been dubbed Phidippides cardiomyopathy - after the fatal heart damage suffered by the original marathon runner.
Indeed, the phenomenon seems to have been coined rather recently, after the publication of this journal article:
Phidippides was a Greek messenger who experienced sudden death after running more than 175 miles in two days. In today's world, marathon running and other endurance sports are becoming more popular and raising concern about sudden deaths at these events. Once etiologies such as hypertrophic cardiomyopathy, anomalous coronary arteries, and coronary atherosclerosis have been excluded, there is now an additional consideration termed Phidippides cardiomyopathy. Because endurance sports call for a sustained increase in cardiac output for several hours, the heart is put into a state of volume overload. It has been shown that approximately one-third of marathon runners experience dilation of the right atrium and ventricle, have elevations of cardiac troponin and natriuretic peptides, and in a smaller fraction later develop small patches of cardiac fibrosis that are the likely substrate for ventricular tachyarrhythmias and sudden death.
Conclusion: the scientific basis of too much endurance exercise seems to have been established. We've seen this way too often -- distance runners who look fit as a fiddle dropping dead suddenly at endurance events. But there was a precursor to Jimmy Fixx, Alberto Salazar and countless others who collapsed while running such events. It was Phidippides. And the phenomenon is now called "Phidippides cardiomyopathy."
Observation confirmed by apparent scientific evidence. Who does not agree with this now?
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