Endurance Athlete Heart Rates Reveal Genetic Roots

New research suggests that very low resting heart rates in endurance athletes may reflect inherited biology alongside training adaptations.

Topline
A large study published in Circulation indicates that some endurance athletes are genetically predisposed to pronounced bradycardia, meaning their very low resting heart rates may be partly inherited rather than solely caused by intense training.

Study Details

Endurance athletes are well known for having low resting heart rates, often viewed as a sign of cardiovascular fitness. However, extremely low heart rates can raise clinical concerns in nonathletic populations. This new study, conducted by The University of Melbourne, explored whether genetics helps explain why some athletes develop profound bradycardia while remaining healthy.

The research was published in Circulation and focused on endurance athletes with resting heart rates at or below 40 beats per minute, a range often considered a clinical gray zone.

Methodology

Researchers studied 465 endurance athletes and compared them with non athletic individuals. They used a heart rate–associated polygenic risk score to estimate genetic susceptibility to slower heart rhythms. This score reflects the combined influence of many genetic variants known to affect heart rate.

The analysis accounted for age, sex, fitness level, and structural heart changes commonly seen in trained athletes, allowing the researchers to isolate the role of genetics from training alone.

Key Findings

• Endurance athletes had lower heart rate–associated polygenic risk scores than non athletes.

• Athletes with bradycardia showed greater cardiac remodeling, including larger heart size with preserved function.

• Genetic predisposition independently predicted lower heart rates, even after adjusting for fitness and heart structure.

• Very low heart rates and brief sinus pauses were common and well tolerated, with no increase in serious arrhythmias or adverse outcomes over five years.

Implications for Practice

For patients and athletes:
These findings suggest that very low resting heart rates in well trained endurance athletes may be a normal and benign trait, especially when present without symptoms. Genetics may partly explain why some individuals excel in endurance sports and tolerate heart rates that would otherwise be concerning.

For clinicians:
The study highlights the importance of context when evaluating bradycardia. In endurance athletes, especially younger and highly fit individuals, marked bradycardia may reflect inherited sinus node physiology rather than disease. Differentiating genetic and training-related bradycardia from pathological causes could help avoid unnecessary testing or intervention.

At the same time, clinicians should remain cautious when low heart rates occur in nonathletic or symptomatic patients, where bradycardia is more likely to reflect acquired electrical system disease.