EXTREME ATHLETES--TOO MUCH OF A GOOD THING? Exercise is good for you, there is no doubt about it. But we humans are always taking things to extremes, and there is a point where even exercise can turn bad. Endurance athletes are a breed apart, performing feats of astonishing strength and stamina. The record at the time of writing is 59 successive days running a marathon, but no doubt this has been broken since. Interestingly, endurance cycling is one of the toughest sports for your heart, probably because of the combination of large leg muscles needing steady maximum blood flow and the intermittent peaks of intense work for the arms and upper body. Top blood pressures of 200 mgHg are common during rapid mountain climbs as in the Tour de France. The cyclists must also keep this up for long periods--up to five hours-- compared to the two to three hours for a marathon. Overall, endurance cyclists do well in general health, with mortality reduced by 41 percent and life extended by 17 percent.

6 But a significant proportion do develop heart abnormalities, about 50 percent more than in the general population. These include a wide range of arrhythmia types including atrial fibrillation. A thick (or hypertrophied) heart wall is much more prone to rhythm abnormalities. When 46 athletes (37 cyclists) who had these abnormalities were followed up over five years in one study, 18 had a serious cardiac event. Nine of them (all cyclists) died within two years. We must always remember that evolution balances the increased risk of overstimulating the heart with the benefits for immediate survival in times of danger. Extreme exercise saves lives in an emergency but is risky as a modern lifestyle choice! Chapter 5 6. D.

W. T. Wundersitz, B. A. Gordon, C. J. Lavie, V. Nadurata, and M.

I. C. Kingsley, "Impact of Endurance Exercise on the Heart of Cyclists: A Systematic Review and Meta-analysis ," Progress in Cardiovascular Diseases 63 (2020): 750-761.