For over a century, athlete’s heart has been a hotly debated disease. With the recent death of Alexander Dale Oen a quick review of the data wouldn’t hurt.

Athletic bradycardia is a below average heart rate an athlete experiences chronically as a secondary effect of their aerobic training. If the attending physician is unaware of the training status of the individual, then he may mistake it for a heart attack stemming from a thyroid or electrolyte imbalance.

In 1899, Prof. Henschen wrote a paper detailing how the hearts of competitive cross country skiers were larger and more defined than their sedentary counter-parts. This hypertrophy of the muscle was generally considered normal and thought to be a side-effect of training. Today, athlete’s heart is defined as a combination of bradycardia (heart rate below 50bpm), cardiomegaly (an enlarged heart) and cardiac hypertrophy (which is the thickening of the muscular wall of the left ventricle). This combination leads to very high stroke volumes even at rest. During their annual physical, an analysis of the heart should be completed simply to ensure that the sounds made during the cardiac cycle are healthy and no irregular beats are occurring.

This is different from sudden cardiac death which grabs far more headlines. It was discussed previously here. It is important to keep in mind that while marathoners, triathletes and ultra-marathoners will suffer from sudden cardiac death, their overall rate of death from heart disease is 40% lower than their sedentary counter-parts. What appears to happen is that during and shortly after an extreme endurance event, not only is there extreme muscle damage but also extreme stress placed on the heart and the liver. Sometimes it seems that this stress overwhelms the athlete and a heart attack ensues. Given the effort being made (or that had just finished) the athlete’s heart succumbs to the stress far faster than it normally would have. Jim Fixx (1984), Flo Hyman (1986), Hank Gathers (1990), Sergei Grinkov (1995) and Korey Stringer (2001) all suffered sudden cardiac events leading to death. While of very low probability, cleary it can and does occur with some frequency.

If you do not have a heart defect and are not at high risk of heart disease- cardiovascular endurance training in any form can be a part of your training. Should you on the other hand be at risk, keeping the distance less than 10km would be a wise precaution.

Also, remember, as discussed here, even those with full heart failure have demonstrated huge benefits (increased VO2, decreased resting heart rate, decreased resting stroke volume, etc.) from a medically supervised exercise regimen. Thus investing in some form of aerobic training is always a plus but consult your doctor should you be in a high risk category. We’ll see you at the track.