Runners often demonstrate a significantly lower resting heart rate (RHR) compared to the general population. RHR is the number of times the heart beats per minute while the body is at rest. This low rate is a visible sign of cardiovascular fitness and the heart’s adaptation to consistent endurance training. Physiological changes from running allow the heart to function more efficiently, requiring fewer beats to circulate the necessary blood volume.
Defining Athletic Bradycardia
The typical RHR range for a healthy adult who does not engage in regular aerobic training is between 60 and 100 beats per minute (bpm). Medically, a low resting heart rate is defined as bradycardia, meaning the rate is fewer than 60 bpm. For well-trained endurance athletes, however, a low rate marks a highly efficient cardiovascular system, not a problem.
The clinical term “Athletic Bradycardia” describes this condition in physically fit individuals. Many recreational runners see their RHR fall into the 40 to 60 bpm range, which is normal for their fitness level. Elite endurance athletes, such as marathon runners, often exhibit RHRs as low as 30 to 40 bpm due to extreme cardiovascular conditioning. This lower rate indicates a strong, well-adapted heart muscle that efficiently manages the body’s resting demands.
How Aerobic Training Remodels the Heart
The primary reason running lowers the RHR is the heart’s structural and neurological adaptation to regular aerobic stress. The first significant change is the strengthening and enlargement of the left ventricle, the heart’s main pumping chamber. This physical remodeling, often called “athlete’s heart,” allows the ventricle to fill with a greater volume of blood and contract with more force.
This increase in efficiency translates directly to a higher stroke volume, the amount of blood pumped out with each beat. Since a runner’s heart pumps a larger volume of blood per beat, it requires fewer beats per minute to meet the body’s resting need for oxygen and nutrients. The cardiac output, the total volume of blood circulated per minute, remains normal, but it is achieved through high stroke volume and a low heart rate.
A shift in the autonomic nervous system balance also contributes to the low RHR. Endurance training enhances the influence of the parasympathetic nervous system, which is responsible for “rest and digest” functions. This enhanced influence is known as increased vagal tone, named for the vagus nerve that acts as a brake on the heart’s natural pacemaker. The increased vagal tone actively slows the heart’s intrinsic rate, causing the resting heart rate to fall.
Accurate Measurement and Monitoring
Monitoring RHR is a simple, non-invasive way for runners to track recovery and overall fitness. To establish an accurate baseline, RHR should be measured first thing in the morning, immediately upon waking, and before getting out of bed or consuming caffeine. Measuring the pulse manually at the wrist or neck for 15 seconds and multiplying by four is an effective method.
It is helpful to track the RHR over several days to establish a true baseline average, as a single day’s reading can be skewed by external factors. Wearable technology, such as fitness trackers, can provide continuous RHR data, though a manual check can confirm the accuracy of these devices. A slight elevation in RHR—perhaps 5 bpm above the established baseline—can be an early indicator of poor recovery, overtraining, dehydration, or an impending illness.
Low RHR: When to Seek Medical Guidance
While a low RHR is typically a benign sign of fitness in a runner, it is important to recognize when it may signal a deeper health issue. Athletic Bradycardia is considered physiological and safe when the individual remains asymptomatic. The heart’s electrical system must still function normally, meaning the rate increases appropriately during exercise.
A low heart rate warrants medical evaluation if it is consistently accompanied by concerning symptoms. These warning signs include:
- Chronic fatigue that interferes with daily life.
- Lightheadedness, dizziness, or episodes of fainting.
- Shortness of breath or chest pain, which require immediate medical attention.
Pathological bradycardia, a slow heart rate caused by an underlying medical condition, must be ruled out by a doctor. This is especially important if the RHR drops below 30 bpm during waking hours or fails to increase with exertion.