Can Prolonged Exercise Damage the Heart
Several scientific studies have demonstrated the appearance of cardiac muscle proteins after bouts of prolonged exercise. (1,2,3,6) The basic question is with regard to whether prolonged exercise can actually cause myocardial necrosis. Necrosis has been documented when rats swam for a period of 5 hours. (2) However, this same study found no evidence of ischemic injury in swims of 1 to 3 hours in duration.
Although elevated levels of enzymes associated with injury have been documented, there is evidence that the situation is normalized in 24 to 48 hours. (1) The question remains if prolonged exercise can actually damage a healthy heart. There is evidence of sudden cardiac deaths both during and after marathon races. (7)
These published data indicate that marathoners may experience elevated enzymes such as Troponin indicative of damage to the heart, either during or up to 24 hours after the event. Time seems to be a major factor when it is more than 3 hours, which could include other sports such as the Ironman and cross-country skiers. According to several of these studies, it is not uncommon for a small percentage of endurance athletes to exhibit elevated troponin levels after exercise, as well as abnormal heart wall motion, as indicated by echocardiography. (1,2,3)
Given the data as stated above, should there be any deep concern with regard to prolonged exercise and heart function? This is an important question because it relates to the necrosis, or death, of heart cells. A similar phenomenon has been observed with regard to skeletal muscle cells. (5) Unaccustomed exercises, especially those that utilize eccentric muscle contractions (downhill running), result in the release of cytosolic enzymes and myoglobin. However, this has been shown to have a protective effect for future soreness episodes.
There is also evidence available that indicates that prolonged exercise, the magnitude of a marathon, does not adversely affect the hearts of healthy individuals. (4) These researchers examined cardiac enzymes such as Troponin, as well as echocardiography, and found all parameters to be within normal limits following the marathon. However, events lasting more than 3 hours may need further investigation.
Of course, all of the athletes that were tested were “asymptomatic” for heart disease. In fact, the vast majority of scientific investigations still support endurance exercise as being extremely beneficial for the heart and protects against the development of coronary artery disease. The big questions is always related to if the potential benefit is worth the potential risk.
The answer to the original question seems to be that “No” that there is no need for concern, but there should be an awareness of these preliminary research studies. Athletes who engage in these types of activities should perhaps undergo serial cardiovascular examinations in an effort to uncover subtle evidence for myocardial dysfunction.
References
1) Apple, FS, et. al. “Release Characteristics of Cardiac Biomarkers and Ischaemia-modified Albumin as Measured by the Albumin Cobalt-binding Test after a Marathon Race.” CLINICAL CHEMISTRY, 2002; 48:1097-1100.
2) Chen, YJ, et. Al. “Cardiac Troponin T Alterations in Myocardium and Serum of Rats after Stressful, Prolonged Intense Exercise.” J Appl Physiol, 2000;88:1749-1755.
3) “Distance Events: The Risk of Going Long, Peak Performance, http://www.pponline.co.uk/encyc/0679.htm
4) Lucia, A., et. al. “Short-term Effects of marathon Running: No Evidence of Cardiac Dysfunction.” Med Sci Spt Exer, 1999; 31(10):1414-1421.
5) McCardle, WD, Katch, FI, and Katch, VF. EXERCISE PHYSIOLOGY:ENERGY, NUTRITION, AND HUMAN PERFORMANCE. Lippincott Williams and Wilkins, 5th Ed. 2001.
6) Neumayr, G. Gaenzer, H. Pfister, R. and Schwarzacher, S. “Plasma Levels of Cardiac Troponin I after Prolonged Strenuous Endurance Exercise.” Am J Cardiol 2001;87:369-371.
7) Noakes, TD. “Heart Disease in Marathon Runners: A Review. Med Sci Sports Exerc, 1987; 19:187-194.
8) Siegel, AJ, et. Al. “Normal Post-Race Antimyosin Myocardial Scintigraphy in Asymptomatic Marathon Runners with Elevated Creatine Kinase MB Isoenzyme and Troponin T Levels.” CARDIOLOGY, 1995;86:451-456.