By Team ICG® Master Trainer Jim Karanas

“Making News” in the March 2012 IDEA Fitness Journal reminded me of something I investigated years ago, of interest to indoor cycling instructors.  The article was “Endurance Exercise Linked to Heart Damage Risk.”

In 2006, prior to my first ultra-distance bicycle race, the Furnace Creek 508, my coach asked me to have a full physical, including an echocardiogram.  It turned out that I had an enlarged left ventricle as a result of rigorous endurance training over 35 years, and two heart murmurs (leaky valves).  I was in the best physical condition of my life.  I completed the 508 and qualified for RAAM, although I decided not to pursue RAAM for several reasons.  One was growing evidence that rigorous endurance training might negatively impact heart health.

A muscle enlarges (hypertrophies) with specific training.  When weight lifters train for strength, muscle may hypertrophy.  When body builders train, they seek hypertrophy specifically.  An endurance athlete”™s heart naturally hypertrophies because of the demand placed on it to supply blood and oxygen to working muscles.

My cardiologist agreed that my condition was not dangerous or abnormal, but should be watched.

“Endurance Cycling Tied to Lasting Heart Damage” by Nathan Seppa was published in Science News in 2005.  It claimed that people who compete in grueling long-distance bicycle races could harm their hearts.  Blood samples revealed the cyclists had over twice as much B-type natriuretic peptide (BNP), a natural compound that identifies risk for heart failure, as a control group of golfers who were healthy but hadn”™t done competitive cycling.

BNP is a 32-amino-acid polypeptide secreted by the ventricles in response to excessive stretching of the heart muscle.  BNP is elevated in patients with abnormal left ventricle function and correlates with congestive heart disease.

I found several studies correlating BNP with left ventricle hypertrophy in hypertensive patients.  One study found that cycling athletes had significantly larger left ventricles than hypertensive patients without elevated BNP.  The researchers concluded that BNP is elevated only in patients with enlarged left ventricles due to hypertension, not intense cardio exercise.

I discussed this with several indoor-cycling instructors, including my colleague Joan Kent.  Almost immediately, Joan suggested that BNP might be nothing more than a marker of hypertrophy, regardless of cause — heart damage, hypertension, or high-volume, high-intensity endurance training.  Since the heart can hypertrophy for more than one reason, it”™s over-extrapolation to assume that the association of BNP with both good and bad factors necessarily links the factors.  (Yes, she actually talks that way.)

I kept researching.  Several studies confirmed elevated BNP in endurance athletes, although exercise-induced BNP increases are poorly understood.  These studies correlated increased BNP with levels of cardiac troponins, another indicator of heart disease, specifically associated with muscle damage.

The studies confirmed increased BNP in a majority of healthy athletes after prolonged strenuous exercise, although BNP may increase not from myocardial damage, but as a protective or growth-regulating mechanism.  They stated that exercise-induced increases in BNP are not the same as elevated BNP associated with heart disease.  Joan countered that, again, it”™s the same BNP, but may just be associated with hypertrophy, rather than disease.

The best study was “Competitive Exercise in Professional Road Cyclists” in Medicine & Science in Sports & Exercise (2003).  The study questioned conclusions of heart damage in apparently healthy endurance athletes.  It investigated myocardial stress in professional endurance athletes after strenuous, competitive physical exercise by looking at BNP, cardiac troponins, and EKGs.

None of the athletes showed pathology upon cardiac examination.  BNP was elevated, but, based on troponins and EKGs, strenuous endurance exercise in professional road cyclists was not found to result in structural myocardial damage.

The study cited in IDEA Fitness Journal  was published in the European Heart Journal in 2011.  Investigators uncovered evidence that some athletes who participate in extreme endurance sports (alpine cycling, ultra-triathlons, marathons) might damage the right ventricle of the heart.  Notice this article said right ventricle, which pumps blood to the lungs, not left ventricle, which pumps blood to the body and was examined in other studies.

What does this mean to the indoor-cycling instructor?

Perhaps nothing.  Scientific findings vary with new hypotheses.  The fact that the subject continues to come up, however, suggests that we should pay attention to it.

As a fitness professional, my concern is the unbalanced view given to people we train. We have all experienced our students unlocking their potential through their indoor-cycling experience.  We may need to stress adequate recovery, not turning every class into a max effort, the benefits of cross-training, and/or using cycling to enhance balance.

Case in point:  The “Triple Crown” is a coveted California jersey given to amateur cyclists who complete three double-centuries in a season.  In 2011, one of my students got it.  I congratulated her and asked about her recovery plans.  She told me she was going for the “1000-mile club” (first time I”™d heard of it) and planned to do five before the year was over.

As a 58-year old endurance athlete with an enlarged left ventricle, two heart murmurs and a tendency to train too much without proper recovery, I”™ll continue to stay informed and share my findings with you.



Jim Karanas
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