Heart Rate Variability (HRV): What It Is, What It Is Used For, How To Interpret It

Today we will talk about a parameter that can be very useful for us as a measure of our rest: HRV or Heart Rate Variability.

We explain what it is, what it is for and how we can interpret it.

What is HRV or Heart Rate Variability?

HRV stands for Heart Rate Variability, or” Heart Rate Variability “and measures the time interval that separates one heartbeat from another and how constant it is over a period of time.

Contrary to what one might think, greater variability is a good sign .

How HRV works

HRV is the cardiac reflex of activities of the autonomic nervous system.

Our nervous system is divided into:

Central nervous system (brain and spinal cord: something like the control center and the information highway); and
Peripheral nervous system (peripheral nerves and nodes). This in turn is divided into:

- Somatic nervous system (which controls voluntary actions, such as raise a finger); and
- Autonomous nervous system (which controls involuntary actions, such as breathing or visceral movements).

The autonomic nervous system divides itself into:

Sympathetic nervous system (“fight or flight”, which responds to stress stimuli); and
Parasympathetic nervous system (“rest and digestion”, which attenuates the activation of the organism).

Both subsystems act on our heart pacemakers and affect your heart rate, so your HRV too.

L ‘ interval between two heart beats (between R waves) decreases with activation of the sympathetic nervous system and increases with activation of the parasympathetic nervous system .

Both are always on and their predominance depends on a complex regulatory system, but we could say that those people suffering from a general anxiety trait will have a more general heart rate. high, while those who live more relaxed will have a lower heart rate.

In this image you can see com and there is an inverse correlation between heart rate and distance between beats .

What it is for

Heart rate has been identified as a reliable indicator to infer a person’s psychophysiological state .

What makes your heart pound when you have to speak in public?

The different heart status controlled by heart rate has been correlated with health (physical, mental and emotional) ) of a subject, on numerous occasions.

An increase of 10 beats per minute increases the risk of death from any cause by 12% ( Zhang, Shen y Qui, 2016).

Because HRV responds to changes in nerve activation, it has been studied as a simple, inexpensive, and non-invasive measure to assess a person’s physical and emotional state .

Recovery-in-Sport and HRV

HRV is a useful tool for evaluate the physical state of a subject after training.

However, the more you adapt to the type of work done, the shorter the time needed for the recovery (Hautala et al., 2001).

In this graph we can see that the greater the cardiorespiratory capacity of the athlete (X-axis), the shorter the time it takes to return to the pre-training state (Y-axis) .

Sounds logical, right? Well, let’s see what the real application of this is:

Time	Before	5 ′ post	10 ′ post	15 ′ post	1h post	24h post	48h post
RR (ms)	1036.9	675.7	709.3	741.0	900.3	1011.2	1002.2

As we can see, in moderately trained subjects (we are not talking about professional or similar), the RR interval has recovered almost completely an hour later having finished training, at 24 hours it was already completely normal (Maurot et al., 2004).

And the more trained they are, the faster they are. Indeed, in highly skilled subjects, 30 minutes after finishing the training, the interval was 100% recovered (Seiler, Kuffel, 2007).

What does this mean?

That HRV is NOT a good measure for estimating fatigue in moderately trained individuals who are exposed to normal training, which they are already accustomed to , and although many athletes use HRV in the morning, a point day measurement is not representative, as we have to observe the various trends.

Plews et al., (2014) indicates that for make reliable changes in HRV we have to measure heart variability for at least 3 days if we train ; but, perhaps for a week.

Acute changes

So acute changes are not relevant, for example a reduced HRV on a punctual day, is not a problem nor should you change your training schedule.

HRV is not a useful method for evaluating the recovery of bodybuilder athletes or Powerlifters , that is, if you train in the gym to look and / or be strong, forget about HRV.

In trained gym users, both in hypertrophy and strength training, HRV recovered within 30 minutes after finishing the workout.

However, 48 hours later, his indicators of muscle damage were still high.

And so was his ability to show strength.

So imagine you measure your HRV the next morning and it is normal, perfect, we are training and you notice that you are not well, what happens ?: Since HRV is not needed to measure this, it is useless .

Note-to-nerds

The HRV is a compendium that includes temporal analysis (which is the most studied and to which I have referred throughout the article) e spectral analysis .

In the field it is known as “time-domain analysis” and “frequency-domain analysis”.

In turn, each of these analyzes has a huge amount of values that can be measured and they give us different information .

That is, there is no a single indicator, there are many ( rMSSD, AVNN, SDNN, pNN50, pNN20 UVLF, VLF, LF, HF and their ratios; in addition to non-linear analysis and correlation dimensions ) HRV is really complex.

Spectral analysis has been shown to have mixed certainties : in the systematic review by Bosquet et al. (2008) it was observed that frequency domain trends were changed when study subjects were subjected to different training loads during short ( 2 weeks) periods of time.

That is, the greater the training load, the more the domain HRV frequency was modified .

However, Hedelin et al., (2000) did not observe changes in highly skilled subjects who were recruited on a 6-day retreat and increased their training load day by day until they reached maximum effort. Yes, they were overtrained on purpose (rather, looking for an overreaching).

We continue with the question that if, as proposed by some authors such as Massaro and Pecchia (2016), we are going to make ultra-short or short measurements (about 5 minutes) it is better to look at the spectrum rather than 24-hour measurements, rMSSD is higher .

Heart-rate-variability to measure overtraining

The HRV is a useful measure to know if a subject is overtraining.

Their values are low compared to non-overtrained athletes, but they are still better than sedentary subjects, even if healthy (Mourot et al., 2004). But it is not a measurement, if not a trend of measurement over time .

Health and HRV

Heart rate variability has been linked to health on numerous occasions.

In fact , low cardiac variability has been associated with the development of a large number of diseases .

HRV is revised as a measure with potential (predictor) to detect the risk of death from cardiovascular or other causes (Sen and McGill, 2017) looks very promising, but we need more study.

Application-of-practice

I suppose you’ll think the theory is fine, but how can we apply this:

First, I’ll tell you that for now the fr Resting heart equence is a much more valid measure for estimating recovery status (Bosquet et al., 2008), like health (Zhang et al., 2016) of a person .

If you still want to learn how to use HRV, I recommend reading the reviews by Massaro and Pecchia (2017) and Draghici and Taylor (2016) to understand how a spectral analysis is performed. Then get familiar with the use of the Kubios program .

If you prefer to use the HRV time domain, even knowing that (for lack of further research) it is inferior to other simpler measurements such as heart rate, you can do the following:

Download HRV4Training or EliteHRV , personally I recommend the former.
Take the required measurements until this screen appears:

From there you can take your measurements daily, remember to take them (if you want to see how you evolve) when you wake up, lie on your back on the bed (position is important) and synchronize a chest heart rate band with the APP.

Assess your health

Enter the “insights” part of the APP.

Find the window where you can find your rMSSD values.

Enter ‘article published by Sammito et al. (2019) that I leave you in the description and search in the section “rMSSD” the sex and age group in Table 3 . You will see that “5 ° / 25 ° …” appears above, ie the percentiles, the closer you get to 95, the better the cardiac variability and the healthier you are.
Measure your rMSSD every 2 weeks in the same conditions to check if you are improving heart variability following training.

If you don’t, maybe you should think about adding some aerobic exercise, do you know that” cardio “is good any time of the year? We explain it here.

Evaluating recovery from training

Although heart variability is not an interesting variable to control fatigue, if you have decided to use the HRV4 training, you can be well guided moderately.

The APP will ask you to record stressful factors (travel, rest, food, health …) in order to enter the variables and obtain their logarithms.
On days when, after measuring the heart rate, the values leave the desired range (as shown in the following image), the application itself will tell you that it is a good idea to rest or relax.

Conclusions

Personally, if you see exactly what you see in the picture “Your HRV is lower than your normal values. However, your subjective scores are doing positively “, I wouldn’t go around it and train as planned and as you see fit.