I have completed my initial experiment with daily heart rate variability (HRV) measurements that began in February. As background, if you don’t know about HRV, you can read this post Do You Have a Healthy Heart? to learn what I am measuring and why it matters. You can also refer to my previous readings here: Baseline, March, April, and May.
The fantastic news is that the primary HRV measurement I am evaluating (RMSSD) increased substantially from 29.6 to 37.3 (an increase is a positive improvement). Based on the research papers I had read, I expected that my HRV parameters would benefit from strenuous exercise over a period of several months, and thankfully, my results were consistent with that research.
As I continue to exercise, I will occasionally check to see if my numbers improve and also use the information to determine if I am overtraining. Given that I am only working out 3 or 4 times a week, I don’t think it is likely that I will suffer from overtraining; however I hope to be able to increase my training now that my body has a better level of fitness.
On a related note, I plan to write several posts in the coming months about cognitive abilities and neuroplasticity (the ability of the brain and nervous system to rewire themselves) related to acquiring new motor skills via exercise. This research paper, “Is heart rate variability related to memory performance in middle-aged men?” looks to be a good bridge between these areas of interest.
My ongoing heart rate variability (HRV) measurements continued to show a modest improvement during the month of May. As background, if you don’t know about HRV, you can read this post Do You Have a Healthy Heart? to learn what I am measuring and why it matters. You can also refer to my previous readings here: Baseline, March, and April.
The primary HRV measurement I am evaluating (RMSSD) increased from 28.1 up to 29.6 (and an increase is a positive improvement). In addition, the trend over the second half of the month was dramatically better, so I expect that next month’s reading will be substantially better.
The Central Nervous System and Brain
I continue to find interesting articles and books about the nervous system as well as the brain, and I recently completed reading The New Brain by Dr. Richard Restak.
In his book Dr. Restak writes about sensory adaptations made by the brain when a person loses the ability to see (enhanced hearing is but one example). Another example relates to how a blind person learns to read Braille; however not everyone who learns Braille does so in the same manner.
Some people read Braille using a single finger, and some people use three fingers treating them as a single unit. “Those who read Braille for several hours a day and use several fingers simultaneously develop a kind of merged, giant, large finger,” says Thomas Elbert, a brain researcher in Germany. This “merged finger” phenomenon often leads to the person losing the ability to determine which of the three fingers is actually receiving the stimulus (and not just while reading).
Try the following experiment: Take off your shoes and socks, close your eyes, and have someone lightly touch different toes. Can you correctly identify which toe was touched?
I did pretty well when my wife touched either my big toe or my little toe; however I did no better than random chance when trying to identify between toes two, three, and four. Given how we trap our toes inside of sensory-limiting shoes most of the day, it isn’t that surprising that our brain begins to look at them as a single unit.
As regular readers will recall, I have been taking daily heart rate measurements to determine how exercise improves heart rate variability (HRV), a valuable measure of heart health. You can refer back to my post Do You Have a Healthy Heart? to learn about what I am measuring and why it matters.
Results for April
My seated resting heart rate has shown a decrease from 75.8 beats per minute (BPM) down to 73.1 BPM (a good thing). Also my chosen HRV metric, RMSSD, has increased from 25.6 to 28.1. Remember, increased HRV is what I am after, as a heart that shows a good degree of variability tends to be healthy.
In looking more carefully at my results (baseline, March, and April), the numbers are all fairly similar and within a standard deviation of each other. So rather than worry whether the numbers are “statistically significant” or not, I will be satisfied that the trend is improving.
Prediction: I will need several years of solid exercise before I see the type of improvements I am hoping for (resting heart rate around 60 BPM and RMSSD about 2x or 3x where it is now).
Other Thoughts on Exercise and the Central Nervous System (CNS)
I have spent quite a bit of time reading and studying the roles of the parasympathetic and sympathetic nervous systems. As I learn more, I am absolutely amazed at the incredible complexity that is found in the mind-body connection. As an example, I can review my daily HRV measurements and see EXACTLY which days of CrossFit provided a strenuous CNS workout, and how long it took me to recover (usually 2 or 3 days). At some level my mind processes the intensity of the workout and decides how to regulate my heart rate for the next several days. Pretty cool!
If this idea of mind-body connection is intriguing to you, you might be interested in the following research paper: “From catastrophe to complexity: a novel model of integrative central regulation of effort and fatigue during exercise in humans.” The three key conclusions are as follows:
- “… all physiological functions are … regulated by CNS control mechanisms to ensure that bodily harm does not result.”
- “The conscious sensation of fatigue does not arise directly from the action of metabolites in the periphery, but rather from the regulatory centres in the subconscious parts of the brain, the function of which is to ensure homoeostasis during exercise. Therefore the distinct sensation of fatigue is not directly related to a physical end point, but is rather an interpretation of the effect of the current level of activity on future exercise capacity and any threats that immediate and future events pose to the maintenance of homoeostasis.”
- “As the sensation of fatigue is an emotion rather than a physical state, pacing strategies and their control during self regulated exercise—the journey and not just the end point—are probably the most important phenomena in exercise physiology.”
So remember, that fatigue you feel as you try to finish one more pull up, it’s all in your mind.
The following is a quick post with the results of my heart rate variability measurements for the previous month. You may want to refer back to my introductory post Do You Have a Healthy Heart? and my Baseline Measurements post to have a better idea of what I am measuring.
Modifications to Methods
I am still using my Suunto t6d heart rate monitor to measure my resting heart rate every morning; however I have made a few changes. Instead of measuring in both a seated and standing position, I am now just measuring my seated resting heart rate. And I am measuring for 5 minutes instead of 3, and looking at a 3 minute window instead of a 1 minute window. These changes were made after consulting with two of the authors of studies I referenced in my first HRV post. They felt that a slightly longer measurement would give me a bit better insight.
And since I am no longer recording standing resting heart rate, I am not calculating my orthostatic heart rate (the difference between standing and seated) as it didn’t seem to be indicating anything very interesting.
Over the past month, my seated resting heart rate averaged 75.8 (+/- 4.3) beats per minute. This number was almost exactly the same as the baseline number of 75.2 (+/- 3.8) beats per minute.
My heart rate variability (expressed by RMSSD – the root mean square of successive differences) went down to 25.6 (+/- 7.0) from 34.8 (+/-10.9). This is the wrong direction; however it isn’t completely surprising considering that I have dramatically stepped up my exercise habits over the past month (and may be slightly overtraining). What I hope is that my body adapts to the exercise and increases parasympathetic output which will lead to a much higher HRV measurement.