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New Research Examines Exercise Intensity and Heart Health

By L.K. Regan

Recent research offers new information on the relationship between intense exercise and heart health. Very intense physical exertion is associated with sudden cardiac events, but it's not clear which kinds of exercise help the heart, and which hurt it. Many of us work out thinking it will help our hearts—but increasingly that seems to depend on the type and intensity of the exercise involved.

First the good news: triathlons, despite their intensity, seem to help build a stronger heart by balancing strength and endurance training. A study conducted at the University of Erlangen-Nuremberg in Germany performed MRIs on 26 professional male triathletes and 27 controls. As lead researcher Michael M. Lell, MD, an associate professor at the university, said, "To our knowledge, this is the first study using MRI to investigate the effects of triathlon training on cardiac adaptations."

Cardiac adaptations? Well, the most common cause of sudden cardiac death, Dr. Lell says, is cardiomyopathy—changes in the relative sizes of the heart's chambers and the thickness of the heart's wall, which make the heart pump inefficiently. But this is not to be confused with what may be beneficial adaptations that the heart (which is, after all, a muscle) makes in response to training regimens. "The cardiac adaptations in the elite triathletes we studied were characterized by a balanced increase in left and right ventricular muscle mass, wall thickness, dilation and diastolic function," Dr. Lell said. In short, the heart had trained itself into a kind of perfect balance. "These adaptations reflect the nature of triathlon training, which has both endurance and resistance components," said Dr. Lell.

In other words, the balance of endurance (running) with resistance training (cycling and to some extent swimming, though these also, of course, involve endurance) resulted in changes to the hear that, as Dr. Lell says, "were not associated with sudden cardiac death." Far from it, in fact. The triathletes' resting heart rates (a simple measure of cardiac efficiency) were 17 percent lower than those of the control group.

Compare this to new research on ultra-endurance runners. One might think that it would be impossible to get any fitter than guys who run races held over distances of 50 miles or more. But a study conducted by Liverpool John Moores University and the Countess of Chester Hospital in the UK finds that ultra-endurance runners have a high likelihood of damage to the heart muscle.

This study examined 45 runners at the Lakeland race in England—a 50- and 100-mile race over open land with some serious hills (and potentially very bad weather—particularly the year of the study, when vicious thunderstorms descended). All the subjects had trained appropriately prior to the race and had no known history of heart trouble. Even so, only about half the subjects even completed the race—it's that brutal—and of those, several collapsed at the finish. The 50-mile runners completed the race in an average of 15 hours; the 100-mile runners averaged 36 hours. All the subjects had ECGs taken before and after, and were tested for levels of cardiac Troponin I (a protein the presence of which signals damage to the heart).

In 21 of the 25 runners, Troponin I levels rose significantly—a strong sign of changes to the heart muscle. In three of those it rose enough to suggest significant cardiac damage. While ECGs at the start of the race were normal for an athletic heart, at the end over half the ECGs were showing significant changes, and some were highly abnormal—"bizarre," as described by Professor Sornauroo of the Countess of Chester Hospital, who presented these results at the European Society of Cardiology's Congress in Stockholm. The researchers also say that they have further data to suggest an overall six percent drop in heart function at the end of the race.

As Professor Somauroo summarized his results, "This study suggests that running continuously over 50 or 100 miles may not be good for the heart." In the world of extreme athletics, it would seem, the triathlon still reigns supreme—at least as far as the heart is concerned.