What’s up y’all? Long time no see, but here we are and the plan is to cover a pretty hot topic – recovery and measuring heart rate variability, something that those who take their training seriously have probably heard of.
At exhibitions, people very often ask us about our recovery, or HRV, measurement and the graphs we show you about it on our app. What does it tell? How to read it? How to use it? Why to use it? So, I figured, why not write about it over here! I’ll try to do this using as few too-hard-to-understand terms and words as possible, but if there’s anything that’s unclear for you, please feel free do drop a comment below and I’ll help you!
First a little bit about Emfit QS. We measure HRV throughout the entire night in 3-minute time windows, meaning that in one hour you’ll get 20 HRV measurements, and during a whole night there will be something between 140 and 180 HRV measurements. Then we draw you this nice little pink HRV graph and either a green or red total recovery bar that indicates either declining or rising recovery during the night (we’ll go deeper into the matter of these two a little later). Even better, since Emfit QS is completely non-contact and all automatic, you can don’t have to sweat about measuring your recovery. More reliable than taking just one measurement in the morning (like it usually is done or at least has been done until now)? Absolutely. More convenient than all the strap-ons? Definitely.
This is what our web app’s “main page” looks like at the moment – minus the heart rate, respiration rate and movement data, which got cut out, but you get the idea. We’re also working all the time on bringing even more data over to it. Not that we already aren’t displaying more sleep and recovery data than any other sleep monitor can ever offer you, but we still want to make it better – for you 😉
Recovery and Autonomic Nervous System Balance
Fight or flight. Rest and digest. Do these two ring a bell? The balance between these two is basically what autonomic nervous system balance is at its core. The autonomic nervous system influences the function of internal organs. It acts mainly unconsciously and regulates bodily functions such as the heart and respiratory rate, digestion, pupillary response, and sexual arousal. The autonomic nervous system is divided to sympathetic nervous system and parasympathetic nervous system.
The sympathetic nervous system (SNS) controls the functions of the circulatory system, glands, digestive tract and the urinary system. Its functioning speeds up in stressful situations and during exertion, like exercise. The SNS boosts the body’s performance by i.e. enlarging the airways, speeding up the heart rate and stroke volume, increasing the blood flow of the heart and skeletal muscles, and decreasing the blood flow of the skin and digestive organs. The SNS is the promoter of the fight-or-flight response, corresponding with arousal and energy generation, and inhibiting digestion.
The parasympathetic nervous system (PNS) controls the functions of the glands, circulatory system, digestive system, and metabolic waste system by for example speeding or slowing down the blood flow of these organs. The PNS is the most active when you’re at rest, like sleeping or digesting. The system makes the heart rate slow down, speeds up the functions of the digestive system, and decreases the respiratory rate. So, as some of you may have guessed, this system is the promoter of the rest and digest response, promoting calming of the nerves’ return to regular function and enhancing digestion.
Normally these two cooperate and are at balance. In stressful situations the balance may be shaken, meaning that problems in the organs that the nervous system controls may appear. Anxiety and fear build up stress and thus accelerate the sympathetic nervous system functions. Consequently, relaxing, sleeping, and recovery get harder. On top of that, stress also decreases our defense against infections.
Frequency Domain Analysis – LF/HF
In our app, we define the ANS balance by measuring LF/HF (Low Frequency/High Frequency Ratio), both of which are common frequency domain measures of heart rate variability. LF is the area measured in a frequency band of 0.04-0.15 Hz, and it is considered a state indicator of both sympathetic and parasympathetic nervous systems. HF is the area measured in a frequency band of 0.15-0.4 Hz, and it is considered a state indicator of parasympathetic nervous systems. When these two are in balance, your body is at its optimum: ready for action, but also strong and unstressed.
Emfit QS uses normalized units LFn and HFn, which are expressed as a percentage of the sum of LF+HF, i.e. LFn=LF/(LF+HF). Our diagram displays both LFn and HFn, and ideally, the indicator should stay near the 50-50 shaded line between values of 25 and 75. Deviation beyond 25-75 or 75-25 line may result from insufficient recovery, high or chronic stress, general fatigue or some other malfunction in the body.
Time Domain Analysis – RMSSD
RMSSD, “Root Mean Square of Successive Differences”, is one of the most widely used time domain heart rate variability values. For all the math and other kinds of geniuses out there, it is the square root of the mean of the squares of the successive differences between adjacent heart’s beat-to-beat intervals. And if you don’t understand that last sentence, don’t worry – I don’t really either – we’re not all as smart as the CTO of Emfit and that’s ok!
In scientific literature RMSSD is widely accepted as a measure of parasympathetic nervous system activity and it correlates very well with HF of frequency domain analysis. For efficient recovery from training and stress, it is essential that the parasympathetic nervous system is active, and our body gets sufficient rest and replenishment. With HRV RMSSD value you can monitor what your general baseline value is and see how heavy exercise, stress, etc. factors influence it. When the value gets back to baseline, it indicates your body has recovered, meaning, for example, that your body is ready to take another bout of heavy exercise.
RMSSD can be measured in different lengths of time windows. In our app, RMSSD evening value is the average of all 3-minute time window RMSSD values measured during the first 90 minutes after going to sleep. RMSSD morning value is the average of all 3-minute window RMSSD values measured during the last 90 minutes prior to waking up. Together these two tell you how ready your body is for the new day.
When you look at our app, you see green and red recovery bars in the middle section. When your morning RMSSD is higher than your evening RMSSD, the bar is green – positive recovery trend. On those days you’ll know your body has recovered and you can go lift as heavy weights as you possibly can or run a marathon if that’s your thing. A red bar means that the morning RMSSD is lower than the evening one, meaning that recovery hasn’t been happening. On these kind of days I’d suggest taking it easy when it comes to training. Why? Unless you like the idea of overreaching and overtraining, the smartest thing to do is let your body have the rest it deserves.
RMSSD value is highly individual and depends on age, gender, fitness level, stress level, lifestyle choices, etc. For this reason, one should monitor values for a few weeks, and only after that make conclusions on what kind of implications different values have. Generally, higher values indicate better health and fitness. In short term, RMSSD indicates readiness for the day, and in long term, for example along with training, RMSSD values tend to climb up. Long term decrease in RMSSD may be a sign of approaching overtraining.
Let’s go back to the questions I listed at the beginning:
What does it tell?
Heart rate variability tells how well you’re body has recovered. Great for athletes. Autonomic nervous system balance tells you how well at balance your parasympathetic and sympathetic are, and these were the two systems controlling the fight-or-flight and rest and digest duos. Great for anyone.
How to read it?
It’s pretty simple. Keep measuring for a while, until you start seeing a baseline. When your HRV drops below this level, your body needs rest. On the days when your HRV is at or above the baseline, go for it!
How to use it?
I sort of already answered to this one in the previous question, but basically, it’s your responsibility to make sure your body gets the rest it needs. Unless you’re some super human with a recovery rate that climbs up at light speed and your body has eternal power and strength, you can definitely benefit from measuring your recovery.
Why to use it?
This one is a rather easy one and should be quite obvious especially for anyone who’s even the slightest bit interested in maintaining a rising (or at least not decreasing) trend in physical condition: to avoid overtraining and breaking your body. If you strain your body too much and too often without giving it a break, it will break (pun intended). Meaning, overtraining can set you way back, if you don’t avoid it; Teemu Lemmettylä, a Finnish triathlete and one of our users, has said that overtraining is a serious threat – it can destroy a whole season. He uses our device to prevent that. To finish this recovery measurement lesson I’d like to say one thing: what you can measure, you can manage.