Endurance Sports and the Heart: Positive and Negative Effects of Long-Term Training

Athlete’s Heart

Long-term, systematic endurance training causes profound structural and functional changes to the heart, a phenomenon known as “Athlete’s Heart.” These changes are generally beneficial adaptations that allow the heart to pump blood more efficiently, supporting high-intensity aerobic exercise.

Positive Cardiac Adaptations

Changes in Cardiac Structure

Parameter	General Population	Endurance Athletes	Magnitude of Change
Left ventricular chamber volume	60-75 mL	80-120 mL	+20-60%
Ventricular wall thickness	7-10 mm	10-13 mm	+10-30%
Heart weight	300-350 g	400-550 g	+15-50%
Resting heart rate	60-80 bpm	40-60 bpm	Markedly reduced
Maximum cardiac output	20-25 L/min	35-45 L/min	+50-80%

Functional Improvements

• Lower resting heart rate: Long-term aerobic training can lower resting heart rate to 40-50 bpm, reflecting increased parasympathetic dominance
• Increased stroke volume: More blood is pumped with each heartbeat, so the same blood flow can be achieved with fewer beats
• Coronary angiogenesis: Increased capillary density around the myocardium improves the heart’s own blood supply
• Improved cardiac efficiency: Less oxygen is consumed for the same power output

Cardiovascular Protective Benefits

There is extensive scientific evidence for the protective benefits of regular moderate-intensity exercise on the cardiovascular system:

• Increased high-density lipoprotein (HDL)
• Decreased low-density lipoprotein (LDL)
• Decreased triglycerides
• Lower resting blood pressure
• Improved arterial stiffness
• 30-35% reduction in risk of heart attack

Potential Negative Effects

However, excessive high-intensity endurance training—particularly maintaining an extremely high training volume over the long term—may also bring certain negative cardiac effects, which have drawn increasing attention from the scientific community in recent years.

1. Atrial Fibrillation (AF)

The Athlete’s Paradox

Multiple large-scale studies have shown that long-term, high-intensity endurance athletes (particularly long-distance triathletes, marathoners, and Tour de France cyclists) have an atrial fibrillation incidence rate 2-10 times higher than the general population.

Why does this happen?

1. Long-term training leads to atrial enlargement (particularly of the left atrium)
2. Fibrosis of the atrial wall
3. Long-term parasympathetic dominance of the autonomic nervous system, shortening the atrial refractory period
4. Long-term systemic inflammation (following high-intensity exercise)

Highest-risk groups:

• Those who cycle/run more than 10-15 hours per week for more than 10 years
• Endurance athletes over the age of 50
• Those with comorbidities such as hypertension or sleep apnea

2. Ventricular Arrhythmias

A small number of endurance athletes with extremely high long-term training volumes show an increase in ventricular premature contractions (VPCs), with occasional case reports of ventricular tachycardia. This generally improves after training is stopped.

3. Coronary Artery Calcification (CAC)

Some studies (such as the MESA study) have found that coronary artery calcium scores are higher in high-training-volume white men than in the general population. However, the morphology of these calcified plaques is typically the stable, calcified type (non-fragile), which differs from the unstable plaques of atherosclerosis, and the actual risk of a heart attack remains low.

Balancing Training Benefits Against Risks

Regular Cardiac Evaluation

Endurance athletes over 40 with a high weekly training volume are advised to undergo the following on a regular basis:

• Resting ECG
• Exercise ECG (stress test)
• Echocardiogram
• Once every 2-3 years

The Sweet Spot for Training Volume

Current research suggests that accumulating 150-750 minutes of aerobic exercise per week (at moderate intensity) provides the maximum cardiovascular protective benefit without increasing negative risk. Exceeding 1,500 minutes per week may begin to increase the risk of atrial fibrillation.

Early Symptoms of Atrial Fibrillation

The following symptoms warrant immediate medical attention:

• Irregular heartbeat, alternating between fast and slow
• Sudden shortness of breath during exercise
• Dizziness or near-fainting during exercise
• Unusual fatigue (disproportionate to training load)
• Chest tightness or chest pain

Groups Requiring Special Attention

Group	Precautions
High-training-volume individuals over 50	Regular ECGs, watch for palpitations
Those with a family history of sudden death	Screening for hereditary cardiomyopathy
Hypertension combined with heavy training	Strict blood pressure control
Female endurance athletes	Watch for arrhythmias caused by electrolyte imbalance

Conclusion

There is no doubt that moderate endurance exercise offers tremendous benefits for heart health. However, athletes who maintain extremely high training volumes over the long term do face certain specific cardiac risks, particularly atrial fibrillation. This should not discourage anyone from endurance exercise—rather, it is a reminder that training requires wisdom, not simply more volume. Moderate training, regular medical evaluation, and attention to unusual bodily signals are what will keep your heart beating healthily into old age.

Related Reading

• Cardiac Health in Endurance Athletes: Exercise-Induced Cardiac Hypertrophy vs. Pathological Heart Disease
• Runner’s Cardiac Hypertrophy and Arrhythmia: The Long-Term Effects of Endurance Training
• Cardiopulmonary Adaptations in Swimming: How Long-Term Training Changes Cardiac Structure and Aerobic Capacity
• Cardiac Remodeling from Long-Term Endurance Training: A Longitudinal Echocardiographic Comparison Study