There is a fight-or-flight response to any stress subjected to the body. Individuals with chronic stress (occurring over weeks and months) would typically have responses involving elevated blood pressure, insulin resistance (when the system does not respond to insulin and cannot easily absorb glucose from the blood) and clogging of the arteries due to fat deposits. In the long run, this response further increases the RHR due to cardiac remodelling (changes in the heart). An increased RHR of over 100 bpm (referred to as tachycardia) has been correlated to hypertension and heart failure.
Highlights
- The long-endurance sports of running, cycling, triathlon, etc., have lower RHR as the heart itself increases in size and strength. The ability to pump blood is more efficient and requires fewer heartbeats to supply blood to the entire body,
- Due to endurance training, there are certain adaptations that facilitate an increase in the capacity of the heart to pump more blood. The adaptation includes an increase in the size of the left ventricle as well as an increase in the muscle strength to pump blood more efficiently,
- Endurance training increases fitness by decreasing heart rate, and stress and improving efficiency in blood flow. It is normal to have lower RHR in athletes (30–60 bpm).
Resting heart rate (RHR) is an important indicator of life expectancy, cardiovascular diseases and fitness levels. RHR is the average heart rate in a complete state of rest and is measured first thing in the morning upon waking up. The normal RHR for an average healthy individual is 60–100 bpm (beats per minute).
On the other hand, a reduced average heart rate below 60 bpm (known as bradycardia) may also cause problems like fatigue, exercise intolerance, shortness of breath, dizziness and fainting. This type of bradycardia could stem from a pathological underpinning. Pathological bradycardia may produce chest pain, dizziness, and fatigue due to reduced cardiac output or blood pumped out of the heart.
In the case of athletes, bradycardia is a result of positive physiological adaptations from training and sport. Athletes may have an RHR as low as 30–40 bpm. However, when bradycardia is associated with symptoms like fatigue, dizziness, chest pain and weakness, this may be an immediate sign for you to visit a doctor.
What are the factors affecting RHR?
Emotions: Emotions impact physiological stressors on the body and can result in elevated effects on the heart rate.
- Body temperature: Thermal stressors like heat and/or cold can stimulate dilation responses to modify blood flow to either warm or cool the body, given the circumstances. To protect the body, the arteries dilate and the heart rate increases to increase blood circulation.
- Training: Training stressors raise the heart rate acutely. Once fully recovered, the cardiac muscles adapt by getting stronger, and can chronically lead to an overall decreased heart rate response (both during training and with RHR).
- Dehydration: The blood becomes thicker during dehydration. This leads to increased heart rate to help with blood flow, increasing the RHR.
- Insufficient nutrient intake: Keep in mind that the lower the nutrient intake, the greater the stressors on the body due to inadequate recovery. Acutely and chronically, this can lead to an increased RHR.
- Reduced recovery and sleep: RHR is one of the best indicators of fatigue. More fatigue leads to less recovery and greater RHR.
- Illness: Higher RHR can be a measure of illness or can be a predictor of illness.
Athlete’s RHR for different sports
The long-endurance sports of running, cycling, triathlon, etc., have lower RHR as the heart itself increases in size and strength. The ability to pump blood is more efficient and requires fewer heartbeats to supply blood to the entire body. This is predominantly observed when athletes train in different heart-rate zones and intensities to build capacity. Thus, lower-intensity zones would require a lower heart rate to meet the demands of the exercise. This, therefore, increases the endurance capacity of the individual.
The athlete’s heart
Due to constant training, especially endurance training, an athlete’s heart undergoes certain positive changes. The muscle of the heart, especially the left ventricle, thickens; this increases the ejection of oxygenated blood from the heart around the body and thereby reduces the heart rate. These are some normal adaptive changes in structure and function that helps the athlete perform better, considering the unique demand posed by the sport.
Hypertrophic cardiomyopathy (HCM), however, which is a clinical condition, is fatal and can cause sudden cardiac arrest. As seen in the above image, dilated cardiomyopathy is when the chambers of the heart enlarge to store and pump more blood out while HCM involves increased thickness of the wall and decreased size of the chamber. Due to endurance training, there are certain adaptations that facilitate an increase in the capacity of the heart to pump more blood. The adaptation includes an increase in the size of the left ventricle as well as an increase in the muscle strength to pump blood more efficiently.
It is important to distinguish between an athlete’s heart and HCM. One is an adaptation while the other is a life-threatening genetic disorder. A primary distinguishing factor is the measurement of the wall thickness. Anything over 13 mm is considered a pathological change. With increased wall thickness, the space in the chamber reduces and thereby reduces the amount of blood pumped out of the heart.
Conclusion
Sports need a high level of fitness and recovery. Training intensity and progressions have a huge impact on the body (structurally and functionally). Endurance training increases fitness by decreasing heart rate, and stress and improving efficiency in blood flow. It is normal to have lower RHR in athletes (30–60 bpm). However, it is crucial to check for any abnormalities through regular check-ups to prevent any unnoticed disorders or deaths.
Disclaimer: The contents of this article are for general information and educational purposes only. It neither provides any medical advice nor intends to substitute professional medical opinion on the treatment, diagnosis, prevention or alleviation of any disease, disorder or disability. Always consult with your doctor or qualified healthcare professional about your health condition and/or concerns before undertaking a new healthcare regimen including making any dietary or lifestyle changes.
References
- Rest heart rate and life expectancy.
- Effects of Exercise on the Resting Heart Rate: A Systematic Review and Meta-Analysis of Interventional Studies.
- Assessment of Autonomic Function in Cardiovascular Disease: Physiological Basis and Prognostic Implications.
- Resting heart rate: what is normal?
- Resting heart rate and the risk of hypertension and heart failure.
