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Is Vigorous Endurance Exercise Safe for the Heart?

Over the past three years, several studies have suggested that long-term training for extreme endurance events such as marathons, iron man triathlons, and very long distance bicycle races may cause structural changes that damage the heart. The four concerns are:

1) HIGH BLOOD ENZYMES: Extreme endurance training can cause temporary elevation of enzymes, released by burst heart muscle cells, which return to normal in a few days. The authors feel that, over many years, this can cause scarring of the heart muscle that can cause irregular heart beats. Indeed, one study showed that 12 percent of marathon runners had evidence of this scarring (Mayo Clinic Proceedings, June 2012, 87(6).

2) RIGHT VENTRICULAR DAMAGE: MRIs of endurance athletes' hearts immediately after extreme endurance competition showed damage to the right ventricle of heart. This abnormality disappeared within one week. The left ventricle never showed signs of damage (Eur Heart J., published online December 6, 2011).

3) IRREGULAR HEARTBEATS: Endurance athletes may suffer an increased incidence of irregular heartbeats. Older Elite Cross- Country Skiers who raced the most and had the fastest times in races, had 29 percent higher risk of irregular heartbeats than slower, less trained athletes (European Society of Cardiology Congress, August 29, 2011).

4) ATRIAL FIBRILLATION: Competitive older cross country skiers are more likely to suffer atrial fibrillation, a condition in which the upper part of the heart flutters, rather than contracting in an orderly fashion (European Journal of Cardiovascular Prevention and Rehabilitation, January, 2010; 17(1): 100). Risk factors for atrial fibrillation include a slow heart rate at rest and a large left atrium of the heart. Both factors are very common in endurance athletes, with an enlarged left atrium being found in up to 20 percent of young endurance athletes, and the percentage increasing with age.

I BELIEVE THAT NONE OF THESE FINDINGS SHOULD KEEP MASTER ATHLETES FROM TRAINING FOR THEIR ENDURANCE EVENTS. Here are my answers to each of the concerns:

1) EXPLANATION OF HIGH BLOOD ENZYMES: Your heart is a muscle. The only way to make any muscle stronger is to exercise it so intensely that you damage the muscle. Then when it heals, it becomes larger and stronger. All knowledgeable athletes train the same way. They take a workout intense enough to damage their skeletal muscles which makes their muscles feel sore on the next day. Then they take easy workouts until the soreness goes away when their muscles heal. Then they take their next intense workout. This type of training is called the hard-easy principle.

Virtually all competitive athletes train hard enough to burst their skeletal muscles and leak enzymes from inside muscle fibers into the bloodstream. So, on the day after an intense workout, athletes who are training properly will have high blood enzymes from leaking from skeletal muscles into the bloodstream.

The same also applies to the heart muscle. The higher blood enzymes leaked from the heart on the day after intense exercise is the result of the training effect, and is unlikely to be an indicator of any permanent damage.

2) EXPLANATION OF MRI EVIDENCE OF RIGHT VENTRICULAR HEART MUSCLE DAMAGE: This is the same change that the MRI picks up in skeletal muscles. It is likely to offer the same good and healthful benefits offered to skeletal muscles. It is to be expected because it predicts that the heart muscle will also heal and become stronger.

3) DO MASTER ATHLETES HAVE GREATER RISK OF IRREGULAR HEARTBEATS? This issue is not settled. We have no good studies to prove that extreme endurance athletes are more likely to suffer irregular heartbeats than non-exercisers. All we have are a few small studies.

4) DO MASTER ATHLETES HAVE A HIGHER INCIDENCE OF ATRIAL FIBRILLATION? This month, the most extensive review of the world's scientific literature (J Cardiovasc Med (Hagerstown). 2012 Jun ; 13(6):381-5) shows that:

"• the incidence of atrial fibrillation in sporting middle-aged men is rare (<0.5 percent per year); • a possible facilitating effect on atrial fibrillation is limited to vigorous endurance exercise, not to less vigorous sports; • there are no convincing data to demonstrate that sport itself may be the cause of atrial fibrillation in healthy middle-aged men; and • the beneficial effects of exercise should offset this supposed risk, which, albeit increased, remains low." WHY INTENSE EXERCISE IS GOOD AND HEALTHFUL: Regular physical activity helps to prevent heart disease by increasing blood flow to your heart and strengthening your heart's contractions so that your heart pumps more blood with less effort. It also helps to lower high blood pressure and high cholesterol, and to prevent and treat diabetes. Most heart attacks and strokes occur when plaques lining the arteries break off and pass down an ever-narrowing artery to form a clot that completely blocks the flow of blood to the heart or brain. The area of heart muscle supplied by that artery then lacks oxygen and dies to cause a heart attack. Intense exercise is more effective than just exercising to prevent clotting. In one study, intense exercise helped to prevent clotting by increasing tissue plasminogen activator and plasminogen activator inhibitor-1 far more than low-intensity exercise did (Thrombosis Research, August 2006). Other studies show that vigorous exercise is also more effective in helping people lose weight. Since vigorous exercise can precipitate heart attacks and strokes in people with already blocked arteries, it's a good idea to get a stress electrocardiogram before you start a new exercise program or increase the intensity of your current regimen. If your doctor agrees, gradually work up to the point where you can increase the intensity of your workouts once or twice a week. In 1924, world-famous cardiologist Paul Dudley White claimed that "exercise can't hurt a healthy heart". He is still correct today. Virtually all research data show that regular exercise is highly effective for the prevention and treatment of many common chronic diseases, and for fostering heart health and longevity. Endurance athletes live longer, have less disease, and have stronger and healthier hearts than people who exercise less than they do. See my previous reports on benefits of vigorous exercise: Health Benefits Determined by How Intensely You Exercise

Intense Exercise for Heart Attack Patients?

Intense Training Maintains Endurance in Older People

Intense Exercisers Have Longer Telomeres

Vigorous Exercise Protects Your Heart

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Vitamin D and Calcium Pills Do Not Prevent Bone Fractures
The U.S. Preventive Services Task Force (USPSTF) says there is no value for postmenopausal women to take pills containing up to 400 IU of vitamin D and 1,000 mg of calcium because they do not help prevent bone fractures in older women (June 12, 2012). Fifty percent of postmenopausal women will suffer bone fracture after menopause. Higher doses of calcium and vitamin D may help to prevent bone fractures, but we have no good data to support their use now. No data show that vitamin D pills at any dose, with or without calcium, prevent cancer. We do have data to show that vitamin D pills, at 600 to 800 IU/day, help to prevent falls in older people.

However, doses at or below 400 IU of vitamin D and 1,000 mg of calcium increase the risk of kidney stones, and excess calcium is associated with increased risk of heart attacks. Therefore, the USPSTF states that "with no evidence of benefit, there is no reason to risk harm."

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NSAIDs Do Not Block Delayed Onset Muscle Soreness
To make muscles larger and stronger, you have to damage muscles by taking an intense workout on one day, by feeling sore on the next day, and by going easy for as many days as it takes for muscles to heal and the soreness to go away. This soreness is called delayed onset muscle soreness (DOMS).

A report from the annual meeting of the European League Against Rheumatism (June 11, 2012. Abstract FRI0457) showed that in exercisers with DOMS, taking non-steroidal anti-inflammatory drugs (NSAIDs) such as ketoprofin (100 mg twice a day) increased the amount of pain and delayed healing. Celecoxib (Celebrex, 200mg twice a day) treatment diminished total pain slightly. The authors state that "the inflammatory reaction following muscle injury is essential for recovery".

This supports other studies showing that competitive athletes do not benefit from taking NSAIDs. For example, Ibuprofen did not reduce elevated cytokine levels that signify muscle damage in ultra-marathon runners (Brain Behav Immun 2005; 9: 398-403).

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June 17th, 2012
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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