Many people believe that the frequency of our heart beats follows a fixed rhythm, but that is not the fact. Measurement of the electrical signals from the heart show that tiny differences occur between each heartbeat, also called heart rate variability (HRV). An average heart rate of 60 beat per minute does not mean that the interval between successive heartbeats would be exactly one second. In fact the heart beats may vary from 0.5 to 2.0 second. The interplay between the circulatory system organs and the autonomic nervous system is affected by complex biosignals (such as heart rate) which in turn contribute to a dynamic balance between the brain and the cardiovascular system. HRV is used as an indicator of the activity of the autonomic nervous system. A high HRV, which is evaluated to be associated with good cardiovascular health, indicates dominance of the parasympathetic response, the side of the autonomic nervous system that promotes relaxation, digestion, sleep, and recovery. The research literature has also established that individuals with a range of psychiatric disorders have reduced HRV, but more research in this field is needed.
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What makes a high HRV?
Recent results suggest that HRV is primarily dependent on heart rate, with HRV increasing when the heart beat interval increases (i.e. when heart rate slows), and decreasing when the heart beat interval decreases (i.e. when heart rate quickens). In other words, a high resting heart rate implies a low HRV, which is not healthy either for our cardiovascular system or our brain health. Results from the Nord-Trøndelag Health Study confirm that an increase in resting heart rate over a 10-year period was associated with increased risk of death from ischemic heart disease and also for all-cause mortality. In a recent a study of fifty six undergraduate students in the age of 18-25 the authors found that those who were characterized with a higher fitness according to age- and gender- referenced maximal oxygen consumption norms responded more rapidly and expressed a higher HRV during a cognitive test compared to their unfit counterparts. Another study of thirty nine non-smoking women and men with high blood pressure (59-71 years of age) found that a 10 week intervention of moderate and high intensity training both decreased blood pressure and increased HRV. The authors also found that the effect of training on resting heart rate, during exercise and recovery was more pronounced with higher intensity training.
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What should your resting heart rate be?
According to the American Heart Association the average heart rate for children 10 years and older, and adults (including seniors) is 60 – 100 beats per minute, and for well-trained athletes is 40 – 60 beats per minute. Nevertheless, the most important thing is to know your resting heart rate, and to measure it on regular basis preferably at the same time of the day (not directly after meals and avoid circumstances that can increase heart rate such as smoking, alcohol intake, having fever or pain).
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Thus, the best way to ensure a healthy cardiovascular and cognitive aging is to keep our resting heart rate at a normal level through regular aerobic physical activity in accordance with the guidelines for weekly physical activity. And for those of you who exercise a lot: do not forget to plan your recovery. Getting enough sleep is also essential for healthy heart beats.
Linda Ernstsen, Associate Professor at CERG
Refrences:
- Guidelines for Reporting Articles on Psychiatry and Heart rate variability (GRAPH): recommendations to advance research communication: http://www.nature.com/tp/journal/v6/n5/full/tp201673a.html
- Biophysical characterisation of the under-appreciated and important releationship between heart rate variability and heart rate: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4326239/
- Temporal changes in resting heart rate and deaths from ischemic heart disease: http://www.ncbi.nlm.nih.gov/pubmed/22187277
- The relation of aerobic fitness to cognitive control and heart rate variability: a neurovisceral integration study: http://www.ncbi.nlm.nih.gov/pubmed/24560874
- ACSM’s Guidelines for Exercise Testing and Prescription 9th Ed. 2014: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4139760/
- Effects of aerobic training intensity on resting, exercise and post-exercise blood pressure, heart rate and heart-rate variability: http://www.ncbi.nlm.nih.gov/pubmed/19554028
- Target Heart Rates: http://www.heart.org/HEARTORG/HealthyLiving/PhysicalActivity/FitnessBasics/Target-Heart-Rates_UCM_434341_Article.jsp#.V1iQbfmLTIU
- The Physical Activity Guidelines for Americans (PAG): http://health.gov/paguidelines/
Cardiac Exercise Research Group 