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  • Dr. Mercola

Marathons: Extreme Endurance Exercise Could Be Damaging Your Heart

It's becoming increasingly clear from the recent flurry of scientific studies that overdosing on exercise can have detrimental effects on your health. Too much exercise, particularly long bouts of cardio such as marathon and triathlon training, can do more harm than good—particularly to your heart.

While most Americans would be well served to exercise more, there's no need to work out for more than 45 minutes at a time, and if you exercise effectively, your workouts should be even shorter, which I'll be discussing in a moment.

Getting your heart pumping and your body sweating with regular cardio exercise provides multiple benefits. As your heart rate rises:

  • Your heart pumps more efficiently

  • The amount of oxygen in your blood increases

  • Your body's ability to detoxify improves

  • Your immune system is activated

  • Endorphins increase, elevating your mood

This is just the tip of the iceberg when it comes to the benefits of exercise, but there is a cutoff point beyond which exercise can actually harm your body.

Recent studies are giving us a much better understanding of exercise physiology, and many of our past notions have been turned upside-down, in terms of how long and how hard to push yourself before the benefits of exercise turn into damages.

As you probably know, I am a passionate advocate of exercise and staying fit. But too much of a good thing can have the opposite effect of what you want.

Overdosing on Exercise Can Backfire

Exercising excessively or incorrectly can backfire on your health in a number of ways. For example, the following can occur when you exercise too much or too hard:

  1. Your body can enter a catabolic state, in which your tissues break down

  2. Excess cortisol (a stress hormone) can be released, which not only contributes to catabolism but also to chronic disease

  3. You can develop microscopic tears in your muscle fibers (which may fail to heal if you continue over-exercising), and increased risk for injuries

  4. Your immune system may be weakened

  5. You may develop insomnia, especially if your workout is in the afternoon or evening

However, the most serious risk involves damaging your heart—or worse yet, sudden cardiac death—which will be the focus of this article.

Are You Running the Risk of Sudden Death?

You've undoubtedly been stunned by the occasional news of an elite athlete suddenly dropping dead. These accounts are not as rare as you would hope, and science is finally shining some light on the cause. Marathon runners and triathletes have traditionally been seen as the perfect picture of fitness, the envy of "hobbyists" and professional athletes alike. Running a marathon is on many-a-Bucket-List.

But are the physical demands of this sort of training actually healthy or even safe? The latest research suggests not. High-endurance training puts extraordinary stress on your heart. Although stressing a muscle usually makes it stronger, extremely high stress can have the opposite effect—and your heart muscle is no exception.

Long-distance running leads to high levels of oxidative stress, inflammation, and damage to your heart tissues, producing acute physiological responses that can trigger a cardiac event.

The risk appears to be highest if you're a middle-aged man, due to gender differences and changes that typically accompany aging. Men are two to three times more likely to experience a sudden cardiac arrest, the exercise issue aside.1 One 1984 NEJM study found that you are seven times more likely to have a heart incident while exercising than at rest.2 So, let's take a look at the flurry of studies emerging over the past few years about exercise-related heart damage.

Eight Scientific Studies That May Stop You in Your Tracks

1. According to a study presented at the Canadian Cardiovascular Congress 2010 in Montreal, regular exercise reduces cardiovascular risk by a factor of two or three, but the extended vigorous exercise performed during a marathon raises your cardiac risk seven-fold!

2. In a 2011 study published in the Journal of Applied Physiology, researchers recruited a group of extremely fit older men, all members of the 100 Marathon club (having completed a minimum of 100 marathons). Half of the men showed heart muscle scarring as a result of their endurance running—specifically, the half who had trained the longest and hardest. If running marathons provided cardiovascular benefit, this group would have had the healthiest hearts!3

3. A 2011 rat study published in the journal Circulation was designed to mimic the strenuous daily exercise load of serious marathoners over the course of 10 years. All the rats had normal, healthy hearts at the outset of the study, but by the end, most of them had developed "diffuse scarring and some structural changes, similar to the changes seen in the human endurance athletes."4

4. A 2012 study in the European Heart Journal found that long-term endurance athletes suffer from diminished function of the right ventricle of the heart and increased cardiac enzymes (markers for heart injury) after endurance racing, which may activate platelet formation and clotting. Twelve percent of the athletes had detectable scar tissue on their heart muscle one week post-race.5

5. A 2010 study presented by the American College of Cardiology showed that endurance runners have more calcified plaque in their arteries (which also increases stroke and dementia risk) than those who are not endurance athletes.6

6. A 2011 German study revealed a very high incidence of carotid and peripheral atherosclerosis among male marathon runners.7

7. A 2006 study screened 60 non-elite participants of the 2004 and 2005 Boston Marathons, using echocardiography and serum biomarkers. Researchers found decreased right ventricular systolic function in the runners, caused by an increase in inflammation and a decrease in blood flow.8

8. Research by Dr. Arthur Siegel, director of Internal Medicine at Harvard's McLean Hospital, also found that long-distance running leads to high levels of inflammation that may trigger cardiac events.9

Sustained Elevated Cardiac Output Can 'Tear Apart' Your Heart Tissue

As you can see from the above studies, the research is converging around the considerable risks that high endurance cardio-type exercises pose for your heart. When you engage in this type of training, your heart doesn't have much say in the matter, as it simply responds to biochemical signals from your body to ramp up cardiac output in order to keep up with your level of exertion. You can't "feel its pain" until very late in the game, and at that point, it may be a life-threatening situation.

Extreme exercise causes your heart to massively increase cardiac output, which it may have to sustain for several hours, depending on the duration and intensity of your activity.

Your heart pumps about five quarts of blood per minute when you're sitting. But when you're running, it goes up to 25 to 30 quarts, and it wasn't designed to do this for hours on end, day after day.10 It enters a state of "volume overload" that stretches the walls of your heart muscle, literally breaking fibers apart.

The problem is, many endurance athletes don't allow their bodies to fully recover between sessions. They often live in a perpetual post-workout state, which basically resembles chronic oxidative stress.11 Repeated damage to the heart muscle increases inflammation, which leads to increased plaque formation, because plaque is your body's way of "bandaging" the lining of your inflamed arteries.

Over time, as more damage is inflicted, the heart enlarges (hypertrophy), and forms scars (cardiac fibrosis). MRIs of long-time marathoners reveal abundant scarring all over their hearts. Scientists have also measured elevated cardiac enzyme levels after extreme exercise—just like after a heart attack, which can only mean one thing: this type of exercise is damaging people's hearts.

Endurance Training Can Produce Dangerous Arrhythmias, Myocardial Fibrosis, Hypertrophy and Atherosclerosis

Although researchers don't yet understand all of the factors in this process, they have theorized that high endurance exercise leads to cardiac fatigue, then a flood of catecholamines and adrenalin, which then triggers arrhythmias (abnormal heart rhythms). One common arrhythmia is atrial fibrillation, commonly known as "A-fib."12 A-fib is epidemic among endurance athletes, which sets them up for major increase in stroke risk. Marathoners above age 50 have a five-fold increase in A-fib rates.13

Arrhythmias can progress into full cardiac arrest. According to Dr. James O'Keefe, a research cardiologist and former elite athlete, 50 percent of marathon deaths occur in the final mile of the race, probably due to this cumulative stress on the heart. Dr. O'Keefe summarizes the entire phenomenon nicely in his Mayo Clinic Proceedings paper:14

"Emerging data suggest that chronic training for and competing in extreme endurance events such as marathons, ultramarathons, ironman distance triathlons, and very long distance bicycle races, can cause transient acute volume overload of the atria and right ventricle, with transient reductions in right ventricular ejection fraction and elevations of cardiac biomarkers, all of which return to normal within 1 week.

Over months to years of repetitive injury, this process, in some individuals, may lead to patchy myocardial fibrosis, particularly in the atria, interventricular septum, and right ventricle, creating a substrate for atrial and ventricular arrhythmias. Additionally, long-term excessive sustained exercise may be associated with coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening."

Our Ancestors Did Not Run 20 Miles at a Time

Our Paleolithic ancestors did lots of walking, with occasional sprints, but not extended running. They would run long enough to escape the clutches of a tiger, but there were no marathons happening across the African savanna. One new study lends more credence to the benefits of walking versus running, finding that moderate intensity exercise (walking) produced equal health benefits as vigorous intensity exercise (running), with similar risk reductions for hypertension, hypercholesterolemia, diabetes and possibly coronary artery disease.15

Over the past 30 years, the number of people running marathons has increased 20-fold, while obesity has tripled. Phidippides was the first "marathoner," a Greek messenger who died suddenly after running more than 175 miles in two days. The changes being noted in the heart tissue of long-distance runners, especially in their right ventricles and both atria, have led some physicians to call the condition "Phidippides Cardiomyopathy."16

I want to be perfectly clear that I am not completely against running. If done appropriately, it can be an effective part of your overall fitness plan and may even help you to live longer.17 But you must keep it moderate, and find you own "Goldilocks Zone."

Dr. O'Keefe recommends running no more than 20 miles per week, spread out over three to four days, at a speed of about five miles per hour. If you run farther or faster than that, you may lose ALL benefits, and your health risks can rise to the magnitude of the couch potato—literally—according to the science. The statement written by Hippocrates 2,500 years ago hit the nail precisely on the head:

"The right amount of nourishment and exercise, not too little, not too much, is the safest way to health."

Instead of Endurance Training, Peak Fitness Is Safer and More Effective

Ideally, to get the most benefits from exercise, you need to push your body hard enough for a challenge while allowing adequate time for recovery and repair to take place. One of the best ways to accomplish this is with HIIT, or high intensity interval training, which consists of short bursts of high-intensity exercise, as opposed to extended episodes of exertion. This is a core part of my Peak Fitness program, which Phil Campbell was instrumental in helping me develop. Briefly, a Peak Fitness routine typically includes:

  1. Warm up for three minutes

  2. Exercise as hard and fast as you can for 30 seconds. You should feel like you couldn't possibly go on another few seconds

  3. Recover for 90 seconds

  4. Repeat the high intensity exercise and recovery cycle 7 more times

You can do HIIT by running/sprinting (if you love running), or by using gym equipment such as a treadmill or elliptical machine, or you can accomplish similar benefits without running at all by doing super-slow weight training, as described by Doug McGuff in the video above. HIIT maximizes your secretion of human growth hormone (HGH), optimizes your metabolism and helps regulate your insulin and blood sugar. And it takes far less time than training for a marathon! You can do a complete Peak Fitness workout in 20 minutes or less.

Remember, adequate recovery is crucial between workouts. This includes not only resting your body, but also giving it the nutrients it needs to support recovery. Your post-workout meal can support or impair your recovery. For instance, consuming a fast-assimilating protein such as high-quality whey protein within 30 minutes of your workout will essentially "rescue" your muscles out of their catabolic state and supply them with the nutrients they need to make their repairs.

Any sort of intense exercise should be balanced with strength training, proper stretching, core strengthening, stress reduction, good sleep and an optimal nutrition plan. You'll find much more information about HIIT and other types of exercise in the fitness section of my website.

Not Willing to Give Up on the Marathon? Please Read This First!

If you are an endurance runner or feel your life just won't be complete without completing at least one marathon, please review the International Marathon Medical Director's Association guidelines, which outlines steps you can take to reduce your risk for a cardiac event.18 Don't rely solely on a stress test, because people who exercise regularly are unlikely to show any signs of a problem.

Above all, listen to your body and don't ignore its signals of distress. It's time to put away the outdated "no pain no gain" principal—in this case, it can lead to serious problems with potentially disastrous health consequences.

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