Bradycardia and sports: is it possible to exercise?

Bradycardia is a slowing of the heart rate to less than 60 beats per minute at rest. For most adults, a normal heart rate range is considered to be approximately 60 to 100 beats per minute, although age, fitness level, medications, stress, and underlying medical conditions can influence heart rate. In trained individuals, especially those who regularly perform endurance and mixed exercise, resting heart rates often fall below 60, sometimes reaching 40 beats per minute or even less. [1]

In athletes, a low heart rate is often perceived as a sign of "good fitness," but the line between safe adaptation and the onset of heart disease isn't always clear. Research shows that elite athletes can have resting heart rates below 40 beats per minute and exceed 200 at maximum exertion, reflecting profound cardiac adjustments to regular training. A significant proportion of athletes also experience changes in their electrocardiogram, including bradycardia and conduction delays. [2]

Modern sports cardiology views bradycardia in individuals undergoing exercise as a spectrum of conditions, ranging from a purely physiological response of the "athlete's heart" to the manifestation of serious rhythm and conduction disturbances. In some cases, observation and proper load management are sufficient; in others, a detailed examination and sometimes restriction of participation in competitions or even pacemaker implantation are required. The physician's task is to understand which zone a particular individual falls into. [3]

It is especially important to consider that some dangerous heart conditions, such as hereditary arrhythmogenic syndromes or myocardial diseases, can remain asymptomatic for a long time and first manifest as either bradycardia or episodes of loss of consciousness during training. This is why official recommendations emphasize the need to pay close attention to any symptoms of low heart rate and the importance of pre-competition cardiac screening. [4]

It's important for both the physician and the athlete to understand which signs indicate physiological adaptation and which indicate possible pathology. This article examines the causes of bradycardia in exercisers, the criteria for normal and dangerous conditions, modern approaches to testing, and practical recommendations for organizing training with a slow heart rate. This article is intended for those who exercise regularly, but is also relevant for coaches and physicians working with athletes and amateurs. [5]

Table 1. Resting heart rate ranges in adults

Category of person	Typical resting heart rate range (beats per minute)	Comment
A sedentary adult	60-90	Normal range
Amateur in training	50-70	Moderate bradycardia is often observed.
Endurance or elite athlete	40-60	Physiological "sports" bradycardia
Individual high-class endurance athletes	Less than 40	Significant adaptation is possible, but evaluation of symptoms and ECG is necessary.
An untrained person with a pulse rate of less than 50	Less than 50	Requires analysis of symptoms and risk factors

Mechanisms of "sports" bradycardia: what changes in the heart

For a long time, the primary explanation for low heart rate in athletes was believed to be increased vagal tone, which inhibits the sinus node—the heart's natural pacemaker. Indeed, trained individuals exhibit a pronounced parasympathetic effect: the heart slows down more quickly after exercise, the resting heart rate is lower, and sinus arrhythmia is often visible on the electrocardiogram. However, recent research suggests that the picture is far more complex and involves structural changes in the sinus node itself. [6]

Experimental studies demonstrate that animals develop persistent bradycardia after a period of intense training, which persists even after blocking the influence of the autonomic nervous system. This suggests that remodeling of ion channels in sinus node cells plays a key role, primarily a decrease in the activity of the channels responsible for the pacemaker current. Essentially, the athlete's heart changes "from the inside out," becoming more efficient and working slower with the same or greater blood output. [7]

Clinical observations confirm that sinus bradycardia is extremely common among endurance athletes, sometimes affecting the majority of participants in the sample. In studies of national endurance athletes, sinus bradycardia was recorded in more than half of the subjects, often associated with mild first-degree atrioventricular block and echocardiographic evidence of enlarged cardiac chambers. This is considered part of the "athlete's heart" if it is not accompanied by symptoms or structural myocardial pathology. [8]

Reviews note that the nature of training influences the severity of bradycardia. Endurance sports (long-distance running, cycling, triathlon, swimming) are more often associated with a significant decrease in heart rate and more pronounced sinus node remodeling. Bradycardia also occurs in strength and speed-strength disciplines, but is somewhat less common and usually less pronounced, although specific changes are noted here too. [9]

Thus, "athletic" bradycardia is not simply a nervous reaction to training, but a complex adaptation that includes changes in sinus node function, autonomic balance, and myocardial structure and function. For a physician, this means that a low pulse rate in a training individual, without complaints or other pathological signs, is most often normal. However, it is important to be alert to the possibility that underlying disease may be present under the guise of "athletic heart." [10]

Table 2. The main mechanisms of bradycardia formation in athletes

Mechanism	The essence of the changes	Consequences for the pulse
Increased parasympathetic tone	Increased influence of the vagus nerve on the sinus node	Slowing of the resting heart rate
Reorganization of ion channels	Decreased activity of pacemaker currents in the sinus node	Slower base rhythm
Enlargement of the heart	Increase in stroke volume with each contraction	There is no need for a rapid pulse
Adaptation of vessels and periphery	Improving oxygen delivery to tissues	Lower frequency at the same load
Training experience and type of sport	Long-term endurance training enhances all of these changes.	More pronounced bradycardia

When bradycardia in an athlete can be dangerous

Although bradycardia is physiological in many athletes, there are clear signs that a low heart rate requires serious attention. International recommendations for sports eligibility emphasize that it's not just the absolute heart rate that should be a cause for concern, but rather the symptoms and accompanying changes on the electrocardiogram and echocardiogram. If bradycardia is accompanied by dizziness, weakness, episodes of loss of consciousness, a sensation of heart palpitations, or severe shortness of breath with little exertion, immediate medical examination is necessary. [11]

For physicians and coaches, so-called "red flags" are an important guide. These include episodes of unexplained loss of consciousness, especially during or immediately after exercise, a family history of sudden cardiac death at a young age, the presence of structural cardiac changes based on imaging, as well as high degrees of atrioventricular block and significant rhythm pauses based on 24-hour monitoring. In such cases, bradycardia is not considered a harmless adaptation, but a possible manifestation of serious pathology of the cardiac conduction system or myocardium. [12]

Recent data show that in some athletes, severe bradycardia with pauses longer than 3-4 seconds may be associated not only with training adaptations but also with developing sinus node dysfunction or conduction disturbances. Cases have been described in apparently healthy athletes where sinus pauses longer than 4 seconds were detected, requiring careful evaluation and sometimes leading to pacemaker implantation. However, prolonged sleep pauses in a well-trained individual without complaints may not require treatment but always require specialist evaluation. [13]

The boundaries between acceptable and unacceptable bradycardia depend on the context. For a professional endurance athlete, a resting heart rate of 40 beats per minute without complaints and with a normal electrocardiogram may be a variant of normal adaptation, whereas in an untrained individual, the same values with dizziness and fatigue require immediate examination. Furthermore, even in an athlete, severe bradycardia combined with an inability to adequately increase heart rate during exercise may indicate a disruption of the cardiac chronotropic function. [14]

The issue of medications is also important. Many medications used for hypertension, coronary heart disease, or rhythm disturbances lower the heart rate. This is especially important for athletes, as some medications, such as beta-blockers, not only slow the heart rate but can also impair exercise tolerance and even be prohibited in some sports. With such medications, bradycardia can become excessive and be accompanied by symptoms, requiring treatment adjustments. [15]

Table 3. Signs that bradycardia requires urgent evaluation

Sign	Why is it dangerous?
Loss of consciousness during exertion	Possible manifestation of dangerous arrhythmia
Dizziness, fainting	Insufficient blood flow with low pulse rate
A pulse rate of less than 40 at rest in an untrained person	High risk of pathological bradycardia
Rhythm pauses longer than 3 seconds	Possible sinus node dysfunction or block
Familial cases of sudden death	The likelihood of hereditary heart disease

Diagnosis of bradycardia in athletes

The first step in assessing bradycardia in an athlete is a detailed collection of complaints and anamnesis. The doctor will determine whether there have been episodes of loss of consciousness, severe weakness, chest pain, palpitations, or prolonged periods of extreme fatigue. They will also identify any family history of sudden death or severe heart disease at a young age. Information on the duration and nature of training, any sudden increases in exercise volume, and any potential breaks in training are also important. [16]

Next, a physical examination is performed, including measuring the heart rate and blood pressure at rest, assessing the heart rhythm, listening to murmurs, and examining for signs of heart failure. Even at this stage, the doctor can note how easily the heart rate increases with minor exertion, such as a few squats, and how quickly it returns to baseline. This provides a preliminary indication of the heart rate reserve. [17]

The basic instrumental method is recording an electrocardiogram at rest. In athletes, the electrocardiogram often reveals sinus bradycardia, sinus arrhythmia, first-degree atrioventricular block, and some other changes that, in the absence of symptoms and structural pathology, are considered adaptation. However, the presence of higher-degree blocks, pathological waves, signs of hypertrophy with repolarization disorders, or ventricular arrhythmias requires in-depth diagnostics. [18]

Holter monitoring is widely used to assess the circadian rhythm profile. This method allows for the identification of the minimum pulse rate, pause duration, episodes of conduction disturbances and arrhythmias, and the relationship of symptoms to rhythm changes. Athletes often experience pronounced nocturnal bradycardia and episodes of first-degree heart block during sleep, which may be normal without symptoms. However, pauses and high-degree heart blocks recorded during wakefulness are cause for concern. [19]

Echocardiography is crucial, allowing for the assessment of cardiac chamber size, wall thickness, valve function, and myocardial contractility. An "athlete's heart" is typically characterized by moderate chamber enlargement and good global function, while pathological hypertrophy or dilation with impaired contractility indicates cardiomyopathy or another disease. If necessary, stress tests with pulse and blood pressure assessment, as well as cardiac magnetic resonance imaging, are also performed. [20]

Table 4. Main methods for diagnosing bradycardia in athletes

Method	What does it show?	When it is especially important
Examination and anamnesis	Symptoms, family risks, and stress profile	Always at the first stage
Electrocardiogram	Rhythm, conductivity, signs of hypertrophy	Screening and initial assessment
Daily monitoring	Minimal pulse, pauses, nocturnal arrhythmias	If severe bradycardia is suspected
Echocardiography	Heart structure and contractility	To distinguish an “athlete’s heart” from pathology
Load test	Frequency reserves, load response	When assessing admission to intensive sports

Can I continue training if I have bradycardia?

The decision on whether to exercise with bradycardia is made on an individual basis. International guidelines for sports cardiology emphasize that asymptomatic sinus bradycardia in trained individuals without structural heart disease, even with a heart rate of approximately 40 beats per minute, in most cases does not require restrictions on sports participation. This requires a normal increase in heart rate during exercise and the absence of dangerous arrhythmias. [21]

If an athlete experiences symptoms associated with a low heart rate, the approach changes. In cases of dizziness, weakness, or presyncope associated with bradycardia, a temporary reduction or cessation of intense training is recommended until the examination is completed. In some cases, a temporary reduction in exercise volume alone leads to a partial restoration of heart rate and the disappearance of symptoms, indicating a predominant training adaptation rather than disease. [22]

A special situation is the presence of severe conduction disturbances, such as second- or third-degree atrioventricular block, or a combination of bradycardia and ventricular arrhythmias. In such cases, high-intensity and competitive exercise are most often contraindicated until a full examination and, if necessary, treatment, including implantation of a pacemaker or other devices, have been completed. The recommendations emphasize that athlete safety always takes precedence over participation in competitions. [23]

For physiological bradycardia, proper training planning is key. A gradual increase in volume and intensity of exercise, mandatory recovery days, adequate sleep, and monitoring of overall health are recommended. Monitoring resting heart rate, especially in the morning, helps assess fatigue and the risk of overtraining: a sharp increase in heart rate compared to normal may indicate overtraining or the onset of illness, while an excessive drop combined with lethargy indicates possible overexertion. [24]

Collaboration between the athlete, coach, and cardiologist can be a useful tool. A sports medicine specialist can help determine safe heart rate ranges for different types of training, assess the cardiovascular system's response to stress, and promptly identify signs of adverse adaptation. If you have chronic cardiac or systemic diseases, it is recommended to regularly review your training program in accordance with updated recommendations. [25]

Table 5. Principles of training for bradycardia in athletes

Situation	Load recommendation
Asymptomatic sinus bradycardia, normal heart	Training and competitions are permitted, taking into account the general principles of periodization.
Bradycardia with mild complaints	Temporary decrease in volume and intensity, examination
Bradycardia with fainting, severe symptoms	Temporary withdrawal from sports until diagnosis is clarified
High degrees of blockade, serious arrhythmias	Limit or prohibit competitive activity prior to treatment
Presence of a pacemaker	Individual decision by a sports cardiologist

Medications, chronic diseases, and bradycardia associated with sports

Not all bradycardia in athletes is related solely to training. Many medications used for hypertension, coronary artery disease, heart failure, and other conditions lower heart rate. These include, for example, beta-blockers and certain drugs that affect the cardiac conduction system. In athletes taking such medications, even moderate "physiological" bradycardia can become excessive and cause symptoms. [26]

In the presence of chronic heart disease, the approach to training changes. Current sports cardiology guidelines recommend risk stratification and individualized selection of acceptable exercise loads for individuals with coronary heart disease, cardiomyopathy, congenital heart defects, and rhythm disturbances. In these groups, bradycardia is assessed in the context of the underlying pathology, and acceptable exercise intensity is determined based on the results of an examination, including stress testing and cardiac imaging. [27]

Particular attention is paid to people with implanted devices, such as pacemakers and defibrillators. Here, the issue of bradycardia is directly related to the device settings and the degree of dependence on stimulation. For some athletes with such devices, participation in certain activities is possible with strict adherence to recommendations; for others, intense competitive sports remain contraindicated. In each case, the decision is made in consultation with an experienced cardiologist. [28]

Non-cardiac causes of bradycardia should also be considered. People involved in sports may experience endocrine disorders, primarily hypothyroidism, electrolyte imbalances, side effects of other medications, and even the consequences of infections, including viral myocarditis. In such situations, uncontrolled physical activity and severe bradycardia can worsen the underlying condition, so assessment and correction of the underlying cause take precedence over athletic goals. [29]

For the athlete themselves, the key rule is to inform their doctor about all medications and supplements they are taking, and not to begin taking any medications that affect heart rate without consultation. Many supplements and medications marketed as "fat burners" or "sedatives" can indirectly affect heart rate, blood pressure, and conductivity. Without understanding these effects, attempting to "correct" heart rate or well-being can be counterproductive. [30]

Table 6. Factors increasing bradycardia in an athlete

Factor	Possible mechanism
Beta blockers	Direct decrease in heart rate
Other drugs affecting conductivity	Slowing of impulse conduction in the heart
Hypothyroidism	Decreased metabolism and inhibition of cardiac activity
Electrolyte disturbances	Effect on ion channels and conductivity
Viral myocarditis	Damage to the myocardium and conduction system

Self-monitoring, prevention, and when to see a doctor

With regular exercise, monitoring your resting and exercise heart rate becomes a useful self-monitoring tool. Measuring your morning heart rate immediately after waking helps track your fitness level and fatigue. For most exercisers, a gradual decrease in resting heart rate with a reasonable increase in training volume is a sign of positive adaptation, while a sudden change in either direction, coupled with a deterioration in well-being, is cause for re-evaluation. [31]

Reliable prevention of complications associated with bradycardia includes gradually increasing exercise loads, avoiding sudden increases in volume and intensity, observing recovery periods, and getting adequate sleep. A balanced diet, ensuring the necessary micronutrients and energy, is also crucial, as is avoiding self-medication with medications that affect the heart. Regular preventive medical examinations are especially recommended for athletes with extensive training experience, high training volume, and additional risk factors. [32]

You should consult a doctor if, in addition to a low heart rate, new or worsening symptoms appear: dizziness, episodes of blackouts, fainting, shortness of breath during normal activity, chest pain, severe weakness, or a sudden decline in performance. Equally important are family histories of sudden death at a young age, unexplained fainting spells in close relatives, and previously diagnosed heart disease. In such situations, it is safer to undergo a full examination than to continue training, hoping that the symptoms are "sports-related." [33]

It's helpful to discuss individual "safety rules" with your doctor and coach in advance: at what heart rate and blood pressure levels should training be postponed, what symptoms during training require immediate cessation of activity and seeking help, and what to do in the event of fainting or a sudden deterioration in a teammate's health. Having clear algorithms increases the safety of the training process and reduces the risk of serious consequences. [34]

It's important to remember that even with "perfect" fitness, the heart remains susceptible to disease. Physiological bradycardia in a person who exercises is usually harmless, but it doesn't protect against all possible pathologies. Paying close attention to the body's signals, promptly contacting a doctor, and a balanced approach to training allow you to reap the health benefits of exercise while minimizing the risk of complications associated with rhythm and conduction disorders. [35]

Table 7. When an athlete with bradycardia definitely needs to consult a cardiologist

Situation	Reason for contacting
Fainting or loss of consciousness during exercise	Possible dangerous arrhythmia
New or worsening shortness of breath, chest pain	Risk of ischemia or other cardiac pathology
A sharp decline in performance	Possible cardiac or systemic cause
Pulse rate less than 40 at rest in an untrained person or in combination with complaints	High risk of pathological bradycardia
Family history of sudden death or severe arrhythmias	Suspected hereditary heart disease