The more experienced you get with taking your own measurements you will find that even the smallest technique change can alter readings. A wary Quantified Selfer will be aware of this and control for variation. I found this when I measured Muse Mindfulness vs HRV.
Early in my self-measuring career, I discovered that real-time data can cause a stress reaction I called Freakback and I even tried to describe its anatomy. When your reading is telling you that you are not relaxed you try to force relaxation and that causes stress which raises the stress reading. Eventually the amplitude of stress reaches “not inconsiderable discomfort.”
Each morning I measure my heart rate, EEG, glucose and ketone level. From these readings I get the measure of how much energy I have for the day ahead and can see the impact of the previous day’s activity and sleep on my physiology.
When taking my EEG and heart rate, is it better to take the readings simultaneously or have one precede the other?
The Resulting Potential Action
Based on the result I would alter my morning meditation session to either take the heart rate and EEG reading together or take one reading before the other. This resultant technique I would consistently use to ensure any variability came from external factors rather than my changes in data gathering technique.
What I Did
To measure my heart rate I used a Polar H7 heart rate belt, an iPhone6 and the Heart Rate Variability app. The output was my resting heart rate, rMSSD, Low and High Frequency of Heart Rate Variability (HRV).
For my EEG, I used the Muse headset connected to an iPod5. This gave me a %Calm score after taking a baseline of active thinking.
First, I took readings simultaneously for 15 mornings. This meant I calibrated the Muse, turned on the HRV reading then breathed rhythmically using a breath pacer. At the end of 5 minutes I had both readings.
Next, I took the Muse readings first, then HRV for 10 mornings. The difference here is that during the Muse readings I was counting breaths with eyes closed, during HRV I using a breath pacer. So my method of concentration was different unlike the simultaneous readings.
Finally, for 13 mornings I switched the order with the HRV session first and the Muse session following.
After each session I entered the values manually into a Google spreadsheet for analysis.
What I Learned
The most efficient way for me to measure my EEG and heart rate in the morning is to conduct the readings simultaneously.
Because I could only look at correlations rather than causes in this study it was important to me that when I was calm and balanced the two readings would show some consistency. For example, if I had a poor nights sleep I would think that my %Calm and rMSSD readings would both be lower. So the correlation of the two readings was important to me.
Taking my HRV and %Calm reading at the same time had a strong positive relationship as you can see here from the Pearson correlations:
- HRV before Muse; r = -.14 (No relationship)
- Muse before HRV; r = -.77 (Very strong negative relationship)
- HRV same time as Muse; r = +.48 (Strong positive relationship)
The other methods show interesting differences in readings based on a variance in technique. It seems logical that an upset physiology would show low readings in the same 10 minute period. Or vice versa.
Instead when I shifted from simultaneous readings to using Muse first, there was a very strong negative correlation. That meant when I had a session with a high %Calm EEG reading a lower HRV would immediately follow. Or when I was thoughtful and had low %Calm my HRV was higher. I am open to comments on why that may be. It is a unique outcome that needs further testing as there may some interesting things going on.
When I took the HRV reading before the Muse reading there was no relationship. Somehow that sequence of reading scrambled the signal because there does seem to be a relationship between %Calm and rMSSD when read at the same time. So I have discarded that technique.
As a quick check I compared the average %Calm reading with an average scaled rMSSD (translating it to a scale between 1 – 100) for each of the three techniques. Here is the result:
The average rMSSD was close across the board (45 – 51%) but the %Calm was much lower for the HRV before Calm and much higher in Calm before HRV. Some ideas for this may be that the time pressure of wanting to complete the reading and get on with my day may impact the mindfulness. But that is for further verification.
So with these results I will use Muse and my HRV apparatus simultaneously to measure the waking state of my physiology. I will set up the process so it is automatic and consistent, and begin testing external influences on the morning state.