Running continuously over 50 or 100 miles may not be good for the heart: Study

Aug 31 2010

In 2009, a study was conducted in UK by Liverpool John Moores University and the Countess of Chester Hospital to assess the effects of running in ultra-endurance races.  Typically aimed at super-fit and experienced athletes, these races are held over distances exceeding 50 miles (80 kilometres).  The conclusions suggest that some damage is likely to occur to the heart muscle of competitors, while 12 percent of the study group showed signs of significant cardiac damage.

Commenting on the reasons for the research, Professor John Somauroo of the Countess of Chester Hospital said, "Previous studies into the effects of ultra-endurance exercise examined changes to the shape and function of the heart, and also changes in sensitive markers of cardiac damage including use of the cardiac Troponin I blood test.  However, they did not look at electrical changes to an athlete's ECG, and whether there was any correlation between these and cardiac Troponin I.  Because hospitals commonly use cardiac Troponin I in combination with ECGs to diagnose heart conditions, including heart attacks, this was deemed a useful and potentially enlightening study."

The study recruited 45 runners at the arduous Lakeland race in the north of England.  This 50- and 100-mile (80- and 160-kilometre) event takes competitors over very difficult terrain with many hill sections.  The 2009 event was further complicated by thunderstorms and driving rain.  All the selected runners had trained specifically for this race, had been running marathons and ultra-marathons for over 2 years and had no known heart problems.  Due to the extreme conditions and difficulty of the terrain, only 25 of the 45 runners completed the course (16 did the 50-mile course, and nine the 100-mile course) - and some of these collapsed at the finish.
Ranging in age from 24 to 62, they had blood tests taken for cardiac Troponin I, and ECGs were performed before and after the race: 

• Of the 50-mile competitors, the average completion time was 15 hours, with an average weight loss of 2kg 

• Of the 100-mile competitors, the average completion time was 36 hours, with an average weight loss of 3kg 

• The cardiac Troponin I levels rose significantly in 21 of the 25 runners, and in three it was high enough to suggest significant cardiac damage 

The ECGs at the start of the race displayed the typical features of an athletic heart, with the slow heart rate and electrical changes commonly seen in athletes.  At the finish, there were significant electrical changes in over 50 percent of the ECGs, and in some there were bizarre electrical changes not commonly seen in normal ECGs, either at rest or during exercise.  However, the changes in cardiac Troponin I did not correlate with specific electrical changes on the ECGs.  Further data, to be presented at EUROECHO later this year, will show that baseline heart function was normal, but there was a 6 percent drop in heart function at the finish, which may also be relevant.  Whether these changes reflect undiagnosed cardiac conditions was undetermined.

Professor Somauroo summarised the results, "This study suggests that running continuously over 50 or 100 miles may not be good for the heart.  96 percent of the finishers developed a significant increase in cardiac Troponin I, which can be an indicator of heart muscle damage - and 12 percent showed signs suggestive of significant cardiac damage.  They also developed significant electrical changes on their ECGs and, in some cases, quite bizarre changes.  However, there was no proven correlation between the changes in cardiac Troponin I and the ECG changes."