Micah True, legendary ultra-marathoner, died suddenly while on a
routine 12-mile training run March 27, 2012. The mythic Caballo Blanco
in the best-selling book, Born to Run, True would run as far as 100
miles in a day. On autopsy his heart was enlarged and scarred; he died
of a lethal arrhythmia (irregularity of the heart rhythm). Although
speculative, the pathologic changes in the heart of this 58 year-old
veteran extreme endurance athlete may have been manifestations of
"Phidippides cardiomyopathy," a condition caused by chronic excessive endurance exercise.
Regular exercise is highly effective for the prevention and treatment
of many common chronic diseases, and improves cardiovascular health and
longevity. However, recent research suggests that chronic training
for, and competing in, extreme endurance exercise such as marathons,
iron man distance triathlons, and very long distance bicycle races may
cause structural changes to the heart and large arteries, leading to
myocardial injury. A study in the June issue of Mayo Clinic Proceedings
reviews the literature and outlines in detail for the first time the
mechanisms, pathophysiology, and clinical manifestations of
cardiovascular injury from excessive endurance exercise.
"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,"
says lead author James H. O'Keefe, MD, of Saint Luke's Hospital of
Kansas City, MO. "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."
Dr. O'Keefe and his colleagues present emerging data suggesting that
extreme endurance training can cause transient structural cardiovascular
changes and elevations of cardiac biomarkers,
all of which return to normal within one week. For some individuals,
over months and years of repetitive injury, this process can lead to the
development of patchy myocardial fibrosis,
particularly in the atria, interventricular septum, and right
ventricle, and an increased susceptibility to atrial and ventricular
arrhythmias. In one study, approximately 12% 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 controls.
Although it has been recognized that elite-level athletes commonly
develop abnormal electrocardiograms and atrial and ventricular entropy,
these adaptations traditionally have not been thought to predispose to
serious arrhythmias or sudden cardiac death.
However, it now appears that the cardiac remodeling induced by
excessive exercise can lead to rhythm abnormalities. Endurance sports
such as ultramarathon running or professional cycling have been
associated with as much as a 5-fold increase in the prevalence of atrial fibrillation.
Chronic excessive sustained exercise may also be associated with coronary artery calcification, diastolic dysfunction, and large-artery wall stiffening.
Lifelong vigorous exercisers generally have low mortality and
disability rates and excellent functional capacity, Dr. O'Keefe notes.
He suggests that further investigation is needed to identify who is at
risk for adverse cardiovascular remodeling, and to formulate physical
fitness regimens for conferring optimal cardiovascular health and
longevity.
In a video interview accompanying the article, Dr. O'Keefe stresses
that the report does not detract from the importance of physical
exercise. "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," he explains. "But what this paper
points out is that 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."
Source: Elsevier Health Sciences
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