How Much Exercise Is Too Much Exercise?

A twenty-six-year-old man is running a race. The terrain is tough and mountainous. The weather is hot and humid; the mid-day sun is beating down on him. Despite the hard conditions, the man doesn’t stop for a break; he must reach the finish line. Finally, his goal is in sight as he sprints towards and crosses the finish line. When he has achieved his objective, he shouts “Victory!” then collapses and dies.

The man, of course, is Pheidippides, the legendary runner who sprinted from Marathon to the city of Athens in 490 BC to relay the news of the Greeks’ victory over the Persians.  The Persians outmanned the Greeks by four to one, so winning the battle on the plain of Marathon was newsworthy, but just as important, Pheidippides had to warn the Athenians that the Persians were heading their way. While the story of Pheidippides may or may not be true, the distance between Marathon and Athens, 26.2 miles, is now legendary.  When the modern Olympics were resurrected in 1896, the organizers wanted to stage a final event based on Greek history. They conceived a race from Marathon to the Olympic Stadium in Athens and the marathon was born. Since the first marathon was run in 1896, long distance racing has taken off. Many cities now stage marathons and there were  approximately 541,000 marathon finishers in 2013. Two of the most famous marathons include the New York City Marathon with 50,000 participants and the Athens Marathon- The Authentic, featuring the original course run by Pheidippides.

Why would an athlete, a runner in prime physical shape, die during or after a marathon?  In Pheidippides case, it may have been from sheer exhaustion as he ran to Sparta and back (a distance of 140 miles each way) two days prior and he ran in the hot Greek August heat.  In general, the risk of dying from a marathon is about 0.8 runners per 100,000 runners, a far lower risk of death than in the majority of daily activities.  One would expect that being a runner should have protected Pheidippides from a cardiac related death, but did he overexert himself? Did he exercise too much?

In general, regular exercise is good. The recommended amount of exercise for adults is 150 minutes per week of moderate intensity or 75 minutes per week of vigorous intensity exercise.  Moderate intensity exercise includes walking at 3 miles per hour, bicycling less than 10 mile per hour, water aerobics, doubles tennis, and general gardening. Vigorous exercise is walking uphill, race walking, bicycling faster than 10 miles per hour, singles tennis and heavy gardening.  The highest risk of cardiac death is in the sedentary individual. Any exercise will decrease the risk of dying from heart disease compared to the couch potato. Just standing for more than two hours per day decreases the risk of dying by 10% compared to those who are sedentary.   People performing moderate to vigorous physical activity below the recommended amounts were still able to reduce their rate of cardiac death by 20%. For maximal reduction in cardiac death, 45% compared to those who are sedentary, one needs approximately 547 minutes per week of moderate intensity exercise or 289 minutes per week of vigorous activity.  Interestingly, increasing levels of moderate intensity exercise continues to reduce the risk of cardiac death while the curve flattens or may go up for vigorous activity.  Two large studies recently reported a U shaped curve comparing cardiac death and the volume of exercise.  In people who exercised ten times or more than the recommended amount, the risk of dying stopped going down and trended upward. These studies did have limitations and it cannot be concluded that high volume exercise increases cardiac death. Most studies including both amateur and elite athletes who exercised at high volumes demonstrate a 3 to 6 year increase in life expectancy compared to the general population.

While elite athletes exercising at a high volume may not be dying at a higher rate, they do experience heart problems.  Athletes involved in marathons, endurance cycling events or triathalons have been shown to have elevated levels of troponin right after events. Troponin is a blood enzyme that goes up during a heart attack. While elevation in troponin in athletes does not equate to a heart attack, it suggests that there may be some heart damage due to excessive exercise.  Surprisingly, high volume exercisers have been shown to have excess calcium in the heart arteries, a measure of plaque in the artery.  Excess exercise may paradoxically accelerate heart artery disease, although other traditional risk factors such as diet may also play a role. Athletes are also at a higher risk for atrial fibrillation, an irregular rhythm from the upper chambers of the heart, compared to the general population. Lastly, athletes are prone to sudden cardiac death due to an irregular rhythm from the lower chamber of the heart. Pheidippides was the first report of sudden cardiac death in a long distance runner. In fact athletes who have sudden cardiac arrest without any other underlying heart problem, are said to have Pheidippides cardiomyopathy (disease of the heart muscle). It is felt that chronic high-level exercise causes enlargement of the heart chambers in response to the demand for extra oxygen. This enlargement can cause patchy areas of scarring in the heart. If the scars are in the atria (the upper chambers) the athlete is at risk for atrial fibrillation. If the scars are in the ventricles (the lower chambers) they act as foci for ventricular rhythms and sudden cardiac death.  Chronic high volume exercise can cause excessive wear and tear on the heart and appears to erase the benefits gained by moderate exercise.

While there may such a thing as too much exercise, it must be emphasized that regular exercise is good and will lower the risk for cardiac death. The average exerciser occasionally pushes his or her heart rate to the maximum. The elite endurance athlete pushes the heart rate well beyond the maximum, for days, years and decades.  These athletes can and do experience heart complications. For the average person seeking optimal heart health, too much exercise is less of a consideration than too little exercise. The benefits of exercise clearly outweigh the risks. So start training for that marathon.