HRV heart rate variability measurements seem to have become the big thing in training for fitness or performance right now. It can be used as a great tool, no doubts. It will give us information about yes ….. about what?
As the name indicates it can supply us with valuable information about the status of the cardiac autonomic nervous system or ANS.
That’s it, no more, not about the autonomic nervous system as a whole, nor about the central nervous system as many people claim.
The ANS is a beautiful system, carefully developed and improved during evolution. I’ll keep it short and simple: first the “old vagal system” developed, the system that allowed organisms to freeze or play dead, look at little bugs like the ladybug: what happens if you touch it? It doesn’t start to run faster or to fight since it can’t and it would be futile anyway. It just freezes and it hopes that by playing dead its opponent loses interest. Later in evolution the sympathetic system developed on top of the “old vagal system”, which allowed higher organisms to fight or flee, mobilizing energy resources in order to do that.
And even later another, “new vagal system” developed which became responsible for communication like body language, facial expression and making noises such as talking. So basically the ANS consists of three parts with different functions.
But the famous picture we see in the anatomy books makes us think that the autonomic nervous system fires as a whole, activating or inhibiting all vital functions at the same level or in the same direction. Too bad, that just isn’t true, as research shows.
But anyone measuring autonomic responses like heart rate, HRV, blood pressure, sweating, or breathing, knows that these factors do not all increase at the same time with the same intensity after a stressor. Also even the heart rate in itself and the heart rate variability will dissociate.
Your HRV can go down without a synchronized increase in heart rate, or increase in blood pressure!
This has been proven by Lacey and Lacey already in 1953!
Another misunderstanding is that HRV will tell you something about the status of the central nervous system; that would be like your blood pressure would tell you something about your body temperature, and you know that is not true.
HRV is by far not the magic single measurement telling you everything you need to know about ANS, CNS, fatigue, shape or fitness. HRV tells you about the status of the cardiac autonomic system only. I have tested more than 5000 different people. And often at the same time also testing other autonomic parameters like heart rate, blood pressure, skin conductance, skin temperature and also EEG.
And no, there are no clear relationships between HRV and EEG measurements or DC-potential.
So where does that leave us coaches?
Well, HRV is just another source of information (dependent on the equipment and the correct algorithms used) about the actual status of the athlete, enabling us to adjust the workload of the next training session to the actual status of the athlete, in order to get an optimal training response. But of course HRV is not enough. Personally I distinguish the different training responses for 8 or 9 physiological “blocks”.
1. Central Nervous System
2. Autonomic Nervous System
3. Cardio-Respiratory System
4. Neuro-Muscular System
5. Energy Systems: alactic anaerobic, lactic anaerobic and aerobic
6. Hormonal Systems
7. Detoxification Systems
8. Immune System
9. Passive Movement Apparatus
HRV tells us about a part of the ANS. To measure, monitor and control the other blocks, we need other tests. It’s as simple as that. As an X-ray or MRI cannot be replaced by an ECG.
A low HRV reading cannot tell you about your glycogen levels, your testosterone levels, your CNS fatigue. The other way around if your HRV level is high, it just means that cardiac ANS-wise you might be able to train or perform well, but whether the other systems are recovered, HRV does not tell you. In the end you still might have suboptimal training load and training response! Never follow blindly what a singular HRV test is telling you, always take other factors into account as well.
The one “golden test” that tells us everything about the status of all these systems does not exist and probably never will.
Porges, S.W: The polyvagal perspective. Biol.Psychol. Vol.74, 2007, pg.116-143.
Lacey, J.I; Bateman, D.E; VanLehn, R: Autonomic response specificity. An experimental study; Psychosom. Med. Vol.15, No,1, 1953, pg.8-21.