Heart Rate Variability (HRV) is a parameter that, despite being extremely simple, brings a wealth of benefits when used.
As such, HRV is defined as the temporal variation in heart rate, over a pre-defined period of time (it can never be greater than 24 hours).
As a general rule, it is believed that a person’s heart rate remains stable, for example when at rest, so that the beats are repeated regularly in a rhythmic manner, with a constant time between beats.
Nothing could be further from the truth. The time between beats varies continuously, although this variation is so slight that it is impossible to appreciate it without a suitable recording method. This occurs because the heart rate is regulated by the autonomic nervous system, which consists of two branches, the sympathetic (SNS) and parasympathetic (PNS). It is known as autonomic as it does not depend directly on the control of the brain, but functions independently. Hence the interest in the measurement and interpretation of HRV as an indicator of the state of the autonomic nervous system.
The Parasympathetic Nervous System and the Sympathetic Nervous System in Heart Rate Variability
It should be kept in mind that the autonomic nervous system is nothing more than a reflection of the balance between the Parasympathetic Nervous System (PNS) and the Sympathetic Nervous System (SNS). The PNS predominates in resting situations, decreasing heart rate and increasing HRV. On the other hand, the SNS predominates in situations of mental and physical stress, increasing heart rate and decreasing HRV.
To understand its function in a simple way, it is worth remembering that the PNS controls pupillary contraction, decreases cardiac frequency and contractility, increases insulin secretion, bronchial secretion, and relaxes the bladder and anal sphincters, among other things.
For its part, the SNS dilates the pupil, increases the frequency and contractility, provokes vasoconstriction, increases lipolysis, glycogenesis and glycogenolysis, provokes sphincter contraction and increases sweating.
Thus, these components of the ANS regulate the separation between heartbeats, although this regulation may be influenced by both psychological and physiological factors.
What does Heart Rate Variability provide?
It has been known for some time that HRV analysis can provide a great deal of information on the heart’s ability to adapt to both endogenous and exogenous loads.
It is essential to be aware that HRV has no reference values to compare with. Therefore, as each person has his or her own values, we are dealing with an individual method that allows us to compare the results with those of the same person, taking previous measurements as a reference and seeing the evolution over time. Therefore, it makes no sense to compare the HRV values of one person with another, in fact, we can only compare with our own values and always measured in the same circumstances, to see the adaptation of each person to the different phases of training.
As a general rule, it should be taken into account that HRV, at rest, is high. During exertion, when the frequency increases, the Heart Rate Variability follows an inverse behavior and decreases, becoming more regular beats.
In addition, HRV is an indicator of health status, so having high HRV values is positive, and not only in athletes. If HRV decreases, this is a bad sign, as something is wrong with your health. Therefore, a dominant parasympathetic system is needed, combined with periods of intense, albeit brief, activation of the sympathetic system.
In summary, HRV provides insight into a person’s degree of stress – psychological and physiological – and a person’s ability to recover and adapt to physical exercise.
Heart Rate Variability in Sport
For an athlete, it is evident that HRV can be a good individual marker, both to monitor his or her psychophysical state as well as adaptations to exertion.
If a decrease in HRV is observed, it should be taken into account that it can be a marker of tiredness, fatigue, poor cardiovascular adaptation to effort and overtraining, although in the psychological sphere it can reflect anxiety when facing a competition.
In summary, it can be concluded that the analysis of Heart Rate Variability provides information that helps in the following:
- Evaluate training intensity
- Determine the adaptation to training
- Detect or prevent overtraining states. It is known that HRV decreases after a training session, but that its values recover after 24/72 hours of rest.
- Stress control
As a general rule, high-intensity training, lasting at least three weeks, increases HRV both at exercise and at rest. If this does not occur and HRV does not change or decreases, we may be faced with poor adaptation to training.
This is not an exclusive indicator, although it is a very useful complement, the use of which can lead to three situations:
- High HRV: the athlete is recovered and can train with intensity.
- Maintained HRV: the athlete can train as planned, although not at high intensity.
- Low HRV: the body may be close to the limit. Light cardio only.
Heart Rate Variability analysis as a health indicator
HRV analysis is a good indicator of health status, easily diagnosing states of stress such as burnout, fatigue, exhaustion or anxiety.
In fact, HRV measurement has been used to measure the efficacy of some cardiovascular drugs on the nervous system, as a predictor of mortality and/or the appearance of arrhythmias, assessment of cardiovascular complications in patients with diabetes, control of patients with arterial hypertension….
In turn, it has been gaining importance in the assessment of stress. The current lifestyle implies living with an overactivation of the sympathetic system, which interferes in the repair and recovery processes.
For more information, consult a Sports Medicine specialist.