Is intense cardiac conditioning, such as that required in marathon running, associated with positive or negative health outcomes?

From the Guidelines

Extreme cardiac conditioning, such as that required in marathon running, is associated with an increased risk of sudden cardiac death, particularly in individuals with underlying genetic heart diseases, as evidenced by a 21-year prospective study from Italy that showed a 2-fold higher incidence of sudden cardiac death in athletes compared to nonathletes 1.

Key Findings

• High-intensity and competitive exercise can trigger malignant ventricular arrhythmias, leading to cardiac arrest and sudden cardiac death among at-risk individuals, with a study in the United States identifying HCM as the most common cause of death, accounting for approximately one third of all deaths recorded 1.
• The relative risk of sudden cardiac arrest during exercise is 5-fold higher in athletes compared to nonathletes, and increases over 50-fold for those who are not habitually active but sporadically engage in high-intensity exercise, as found by Siscovick et al 1.
• Physiological changes induced by exercise, such as increased catecholamine levels, acidosis, dehydration, and electrolyte imbalance, can act as triggers and promote the generation of arrhythmias in individuals with underlying heart conditions 1.

Recommendations

• Individuals with existing heart conditions or genetic predispositions should consult healthcare providers before engaging in extreme endurance training.
• Endurance athletes should monitor for symptoms like chest pain, palpitations, or unusual fatigue that might indicate cardiac issues.
• Moderate endurance exercise is likely to provide optimal health benefits, while extreme conditioning may introduce diminishing returns or even risks for some individuals.

Important Considerations

• The relationship between exercise and increased risk of cardiac events is complex, and more research is needed to fully understand the mechanisms involved.
• The benefits of endurance exercise, such as improved cardiovascular efficiency and enhanced metabolic health, should be weighed against the potential risks, particularly for individuals with underlying heart conditions.

From the Research

Positive Health Outcomes

• Distance running has positive effects on a host of coronary risk factors, which may help to explain why chronic endurance exercise is associated with lower coronary death rates 2.
• The robust association of endurance running with improved quality of life and longevity underscores the importance of putting risks into perspective with other well-established health benefits of regular vigorous exercise 3.
• Running is an excellent means of conditioning the cardiovascular system, utilizing both fatty acids and carbohydrates for energy, and resulting in a slow resting pulse rate and a high maximal oxygen consumption 2.

Negative Health Outcomes

• Marathon running is associated with a transient and low risk of sudden cardiac death, with most deaths due to underlying coronary artery disease 3.
• Cardiac biochemical and functional abnormalities are commonly observed transiently following completion of a marathon, although their clinical significance is unknown 3.
• Exercise-induced increases in cardiac biomarkers, such as troponin and brain natriuretic peptide, and acute functional cardiac alterations have been observed in middle-aged non-elite male amateur runners, which may be perceived as physiological myocardial reactions to strenuous exercise 4.
• A significant risk for the development of atrial fibrillation has been identified in 40- to 65-year-old males engaged in intensive endurance exercise 4.
• Ventricular strain slightly decreased after running a 246-km ultra-marathon race, which may be attributed to concomitant pre- and afterload alterations following ultra-endurance exercise 5.

Screening and Prevention

• Careful physical examination of the cardiovascular system, the resting EKG, and echocardiography are useful ways to screen young competitive athletes for cardiomyopathy, the leading cause of sudden death in this age group 2.
• Treadmill testing is often used as a screening test in middle-aged and older runners for underlying coronary atherosclerotic heart disease, the leading cause of sudden exercise-related death in this age category 2.
• Prevention of sudden cardiac death should focus on recognition and investigation of prodromal symptoms, if present, and access to rapid defibrillation and trained medical personnel 3.