The resting heart rate is the number of times the heart beats per minute when the body is completely at rest. It is one of the key vital signs and an important indicator of overall cardiovascular health and fitness. Regular endurance exercise has been shown to lower the resting heart rate over time. This adaptation reflects improvements in cardiovascular function and efficiency.
What is resting heart rate?
The resting heart rate is the number of heartbeats per minute when the body is in a relaxed state. It is usually measured first thing in the morning before getting out of bed or after sitting/lying down for 5-10 minutes. The average resting heart rate for adults ranges from 60 to 100 beats per minute. However, this can vary significantly based on age, fitness level, genetics, and other factors. Highly trained athletes often have very low resting heart rates around 40 bpm.
Factors that influence resting heart rate
Some of the key factors that affect resting heart rate include:
- Age – Resting heart rate tends to decline from birth to young adulthood and then starts to gradually rise again with age.
- Fitness level – More aerobically fit individuals tend to have lower resting heart rates.
- Body size – Larger body size is associated with slightly higher resting heart rates.
- Genetics – There seem to be genetic influences that partially determine inherent resting heart rate.
- Gender – Men tend to have slightly lower resting heart rates on average than women.
- External temperature – Colder ambient temperatures can raise resting heart rate.
- Altitude – At higher altitudes, lower oxygen leads to higher resting heart rates.
- Medical conditions – Some conditions like an overactive thyroid can accelerate resting heart rate.
- Medications – Some medications like stimulants may increase resting heart rate.
So while genetics and age play a role, the factor we have the most control over is aerobic fitness level. Aerobic exercise training is highly effective at reducing resting heart rate over time.
How does endurance exercise affect heart rate?
Endurance exercise refers to continuous, rhythmic aerobic activity utilizing large muscle groups. Running, cycling, swimming, rowing, and cross-country skiing are common endurance exercises.
Performing endurance exercise results in both acute and chronic changes in heart rate:
Acute heart rate changes during endurance exercise
When starting endurance exercise, heart rate immediately increases to meet the demands of the working muscles. As exercise continues at a constant intensity, heart rate plateaus. This is called the steady-state heart rate. It depends on the exercise intensity – the harder the intensity, the higher the steady-state heart rate. Heart rate normally returns to baseline within 5-10 minutes after ending exercise as the body recovers.
Chronic heart rate adaptations to endurance training
If endurance exercise is performed regularly over weeks and months, the cardiovascular system undergoes remodeling to enhance function and efficiency. Some of the chronic adaptations include:
- Increased stroke volume – More blood pumped per beat.
- Higher blood volume – Increased plasma and red blood cells.
- Added capillary density – More capillaries in trained muscles.
- Enlarged left ventricle – Bigger, stronger heart muscle.
- Improved heart muscle contraction – More forceful beats.
These cardiovascular adaptations allow the heart to pump more blood and oxygen to the body with less effort. This is reflected by a decreasing resting heart rate and lower heart rate during submaximal exercise over time.
How much does endurance exercise lower resting heart rate?
Many studies have documented the impact of aerobic training programs on lowering resting heart rate. The magnitude of reduction depends on several factors:
Initial fitness level
Less fit individuals tend to see greater decreases in resting heart rate compared to well-trained individuals from the same training stimulus. In one study, sedentary adults dropping from an average of 86 bpm to 70 bpm after 8 weeks of jogging 45 minutes per day, 4 days/week. Well-trained runners improved from 58 bpm to 52 bpm with the same training.
Exercise duration
Longer duration aerobic exercise generally produces greater reductions in resting heart rate compared to shorter duration workouts when total energy expenditure is matched. For example, a study found 16 weeks of 60 minutes of cycling, 5 days/week lowered resting heart rate by 16 bpm versus 11 bpm with 30 minutes cycling.
Exercise intensity
Higher intensity endurance training drives larger decreases in resting heart rate compared to lower-moderate intensity training when total volume is equal. In one trial, high intensity interval training (HIIT) lowered resting heart rate by 12 bpm versus 8 bpm with moderate steady-state training after 15 weeks.
Exercise frequency
Higher weekly training frequency promotes greater resting bradycardia versus lower frequency when duration is matched. Recent research found resting heart rate declined twice as much doing endurance training 6-7 days/week versus just 4 days.
Total training volume
The combination of training duration, intensity, and frequency contributes to overall exercise volume. In general, greater total weekly volumes of aerobic exercise produce the largest reductions in resting heart rate over a training period. However, very high volumes may eventually lead to a plateau.
Length of training period
The resting bradycardia effect from endurance training intensifies over longer periods of continuous training. However, most of the adaptation seems to occur within the first 3-8 months of consistent training. Beyond that point, the lowering effect on resting heart rate tends to stabilize.
Here is a table summarizing some of the research on how much endurance training lowers resting heart rate:
| Study | Training Program | Subjects | Change in Resting Heart Rate |
|---|---|---|---|
| Wilmore et al. 1996 | 20 weeks cycling or running 45 min/day, 5 days/week | Sedentary adults | -16 bpm |
| Gillen et al. 2013 | 8 weeks cycling 10-20 min/day, 5 days/week | Sedentary overweight adults | -5 bpm |
| Kang et al. 2016 | 12 weeks running 30-50 min/day, 3 days/week | Recreational runners | -4 bpm |
| House et al. 2013 | 8 weeks cycling 45 min/day, 5 days/week | Well-trained cyclists | -2 bpm |
As shown, less fit populations tend to experience greater reductions in resting heart rate from endurance training programs. But even highly trained athletes can lower their resting heart rate further with additional training.
Physiological mechanisms for lowered resting heart rate
There are several complementary physiological mechanisms responsible for the lowered resting heart rate that accompanies endurance training:
Increased parasympathetic tone
The parasympathetic nervous system is responsible for triggering the heart to beat slower and lower blood pressure. Endurance training enhances parasympathetic tone at rest, allowing the heart to relax more between beats and contract less frequently.
Decreased intrinsic heart rate
The intrinsic heart rate is the natural pace the heart wants to beat at in the absence of any nervous system input. Endurance training lowers the intrinsic heart rate, reducing pacemaker activity in the sinoatrial node of the heart.
Improved baroreflex sensitivity
Baroreceptors sense blood pressure and signal to the brain to adjust heart rate accordingly. Endurance training enhances baroreflex function, enabling the heart to automatically regulate to beat slower when blood pressure is low.
Reduced cardiac workload
The remodeling of the heart and vasculature from endurance training allows more blood to be pumped with less effort. This reduced cardiac workload enables the heart to beat at a lower rate at rest.
Increased stroke volume
A larger stroke volume means more blood pumped per contraction. This adaptation means fewer heart beats are required at rest to meet circulatory demands.
Lower catecholamine levels
Endurance training lowers resting levels of stimulatory hormones like adrenaline and noradrenaline that drive heart rate up. This helps facilitate a slower resting heart rate.
Other health benefits of a lower resting heart rate
In addition to demonstrating improved cardiovascular fitness, having a lower resting heart rate has also been associated with several other health benefits:
Lower risk of heart disease
A lower resting heart rate is linked to a reduced risk of coronary heart disease, heart attack, and cardiovascular mortality across populations. This is likely due to enhanced cardiovascular function and efficiency.
Longer lifespan
Population studies consistently associate lower resting heart rates with longevity. This may be attributed to a blend of positive cardiovascular adaptations and inherent genetic factors.
Lower blood pressure
The cardiovascular improvements from lower resting heart rate also translate to reducing average resting blood pressure levels. This contributes to lower hypertension risk.
Less inflammation
A slower resting heart rate is correlated with lower levels of systemic inflammation. Chronic inflammation contributes to multiple diseases and accelerated biological aging.
Better aerobic fitness
A lower resting heart rate serves as a simple proxy for gauging improvements in aerobic conditioning and cardiovascular health from endurance training.
Limitations of a lower resting heart rate
While a lower resting heart rate is generally beneficial, there are some potential limitations in certain individuals:
May not reflect actual fitness gains
Some people naturally have lower resting heart rates unrelated to their fitness level due to genetics, medication use, or medical conditions. So resting heart rate should not be used alone to track aerobic improvements.
Risk of overtraining
In some athletes, an abnormally low resting heart rate below 40 bpm may indicate overtraining syndrome. This requires proper rest and recovery to avoid detrimental overtraining effects.
Masks developing illness
In athletes, failure of resting heart rate to increase as normal during an emerging illness may delay diagnosis and hamper recovery if training continues.
Slow return to baseline after exercise
An extremely low resting heart rate may impede heart rate recovery after intense training sessions. Slower return to baseline heart rate can limit training quality if recovery is incomplete.
Medication interactions
Some medications like beta blockers can drive resting heart rate too low in highly trained athletes, necessitating medical monitoring and adjustment.
Conclusion
In summary, regular endurance exercise predictably lowers resting heart rate over time due to a combination of central nervous system, cardiac, and vascular adaptations. Typical reductions range from 5-15 bpm in previously sedentary adults over 2-6 months of moderate training. Even highly trained athletes can further reduce resting heart rate by 1-5 bpm with additional training volume and intensity. A lower resting heart rate signifies beneficial cardiovascular remodeling. But athletes should also monitor subjective fatigue, stress, and non-training heart rate trends to avoid potential overtraining. For most people, achieving a resting heart rate in the range of 50-70 bpm through regular endurance exercise provides ideal health and performance benefits.