j****y
发帖数: 1714 | 1 【 以下文字转载自 Running 讨论区 】
发信人: joyjoy (joy), 信区: Running
标 题: Extreme Endurance Exercise and heart attack
发信站: BBS 未名空间站 (Sat Oct 5 01:52:16 2013, 美东)
我有同事骑自行车突然心脏病发作死亡。所以看了看锻炼过度和心脏病的关联的文章。
仅供参考：
http://fitness.mercola.com/sites/fitness/archive/2013/08/23/ext
By Dr. Mercola
Do you dread going to the gym for what feels like hours at a stretch? Or do
you avoid working out altogether because you just don't have the time? Then
what I'm about to tell you should be music to your ears: when it comes to
exercise, less is more.
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:
Your body can enter a catabolic state, in which your tissues break down
Excess cortisol (a stress hormone) can be released, which not only
contributes to catabolism but also to chronic disease
You can develop microscopic tears in your muscle fibers (which may fail to
heal if you continue over-exercising), and increased risk for injuries
Your immune system may be weakened
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.” |
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