This past weekend I taught 5 CE's for the Illinois Prairie State Chiropractic Association down in Champaign, IL, and I picked up a couple lessons for myself along the way.
The first lesson I learned is that 5 hours is a lot more difficult to teach than 2 hours! I had done 2 hour versions of the class on several occasions, but this was the first time I had to prepare much longer than that. It was difficult to have all my info sorted in a manner that flowed well and made sense, and even more difficult to keep people's attention for that amount of time.
It still went well, but definitely learned a couple lessons along the way.
The second lesson I learned was in regards to the topic I was teaching. The science behind adaptability and heart rate variability is a very exciting field that is gaining a lot of notoriety and attention. I have been looking at adaptability from the standpoint of an athlete undergoing a periodized strength and conditioning cycle, as exercise physiologists are investigating autonomic responses to training and recovery bouts. Admittedly, I have put myself into an adaptability bubble, so to speak, and regularly converse with other Chiropractors who are investigating the same field. I have conversations with DC's and other health professionals about heart rate variability so often that I forget that the average Chiropractor does not really grasp the concepts or the basic underlying principles of autonomic adaptability and heart rate variability. This post will serve as a very elementary introduction to those topics.
Before I continue I want to put out a shameless plug for my friend and fellow Chiropractor (whose office is less than a mile from my own) Dr. Rob Sinnott. Dr. Sinnott authored a text on Adaptability that puts the topic together beautifully. I had been spending countless hours over the past few years trying to piece together my understanding of the topic of Heart Rate variability and adaptability, and Dr. Sinnott put it all together in a clear and concise text that should be a part of every Chiropractor's library (and taught in schools). You can click on the hyperlink above and get a copy for yourself.
Back in the 1950's, Canadian physiologist Hans Selye wrote a book titled "The Stress of Life," and published a paper in the British Medical Journal called "Stress and The General Adaptation Syndrome" (full text PDF available at the hyperlink I provided). Dr. Selye described the human stress response and how it related in the context of modern life. When humans encounter a stress, we exhibit a fight or flight response, or as he referred to it as "the alarm phase." Most of you reading this are likely aware of the symptomatology of the fight or flight response, so I won't dedicate much time to the specifics of it. Historically, the initial phase of the fight or flight response evolved as a survival mechanism. Think of it this way; several hundred (or thousand) years ago, the likelihood of running into a life threatening situation was considerably higher than it was today. In a life threatening situation survival instincts were necessary to avoid the stressor (lion, tiger, bear, etc). Once the stressor was no longer present, the activity of the sympathetic nervous system would return to baseline, and normal physiology would resume. The body attempting to return to a lowered degree of readiness and normal physiology was referred to as the resistance phase.
Selye put the stress response into a more contemporary context and wrote about the stresses of everyday life. While we rarely encounter life threatening situations, most people in the western world deal with varying degrees of stressful situations in everyday life. These stressful events and situations often times leads to a more constant activation of the very same stress response, to a lesser degree however. Selye referred to this chronic low grade stress activation as the exhaustion phase. He noted that in the exhaustion phase, people would develop a maladaptative response to the chronic stressor, which would put people into a chronic state of low grade fight or flight response. Therefore, the general adaptation syndrome was noted as being a complexity of neuroendocrine symptoms related to heightened sympathetic nervous system activity through constant activation of the hypothalamic-pituitary-adrenal axis.
Increased sympathetic activation coupled with little resistance from the parasympathetic system (rest and digest) was hypothesized to be a contributing factor to many chronic illnesses and disorders of the day (and I would go so far to say that is VERY prevalent in today's society, more so than 60 years ago). Fast forward to today. The activity of the autonomic nervous system is gaining far more attention than ever before in popular media and scientific literature. Vagus nerve stimulation has become a popular method of treating seizure disorder and is being investigated in other disorders such as gastric ulcers. Articles about "hacking" the autonomic nervous system are popping up all over the internet, some of which are claiming that it will be the greatest thing since sliced bread when it comes to overall health and wellness....
Function of the autonomic nervous system has gained a lot of attention in the strength and conditioning world as well. Training is a stress. Period. Training your body is a stress which is designed to elicit physiologic adaptations as well as localized adaptations specific to the area which is being trained. The body's ability to adapt to the stress and recover and become stronger is the key to improving performance during a macrocycle of training. If the body is unable to adapt to a training load, the stress which continues to compound on the athlete leads to a maladaptation similar to what Selye hypothesized nearly 60 years ago.
To combat this and to monitor the effects of the body's physiology during training cycles, more coaches and athletes are turning to simple means of measuring the autonomic nervous system, primarily through heart rate variability. Heart rate variability is an non-invasive tool to measure vagal control of the heart. The vagus nerve exerts a parasympathetic effect on the heart which can be understood through measuring HRV. There are two different basic domains which HRV measures: frequency domain such as high frequency (generally thought to be indicative of parasympathetic activity), low frequency, and high to low frequency ratio. The other domain (which is far more accessible, because you don't need ECG equipment) is time domain. The two most common time domain measures we see in research and application (though these are not the only time domain measures) rMSSD and SDNN. Both of these measure fluctuations and variations in the R-R interval (think QRS complex). Under resting conditions your heart rate should not beat like a metronome, meaning that it should not be a rhythmic one beat per second. There should be variation in time between each beat. Even in a "healthy" heart rate of 60 beats per minute, there should be a fluctuation between each successive heart beat. For example, 4 different heart beats in a row may have four different time measures between them (1.003 sec, 1.006, 1.002, 1.007 would be a better reading than 1.000, 1.000, 1.000, 1.000). The more variation in time between resting heart beat indicates more parasympathetic control. This is a direct method of measuring your body's adaptive capability, and a very simple means of quantifying autonomic function in an individual.
Obviously, I'm not trying to write an exhaustive review of HRV and the ANS, but i found it necessary to at least give background information before moving forward. Again, go up to the hyperlink I provided earlier and pick up Dr. Sinnott's text on adaptability. It was a very clear and easy read which furthered my ow understanding of the topic beyond what I had already learned.