Heart Rate Variability (HRV) is the physiological phenomenon of variation in the time interval between heartbeats. It is measured by the variation in the R-R interval.
About Heart Rate Variability
This biometric measurement was identified back in the 1950’s by Russian scientists working on their space program. RV was the only physiological data that could be transmitted from their spacecraft giving any indication as to the state of the cosmonauts.
Since then, Heart Rate Variability has been studied literally thousands of time in everything from sports performance, to psychology, to nutrition. The amazing thing about HRV is it provides a very good measure of the overall stress that your body is experiencing with a simple non-invasive measurement system.
Autonomic Nervous System
The Autonomic Nervous System (ANS) is a part of the Central Nervous System that regulates key involuntary functions of the body, including the activity of the heart muscle; the smooth muscles, including the muscles of the intestinal tract; and the glands. The ANS is comprised of two additional systems, the Sympathetic Nervous System (SNS), also known as the “flight or fight” system since it is activated in response to stress, and the Parasympathetic Nervous System (PNS), or the “recovery” system since when activated it initiates recovery and relaxation.
Too Much Stress and Not Enough Recovery
The SNS and PNS are always trying to maintain a balance between the two. Just enough stress paired with the right amount of recovery allows for optimal functioning and overall better health.
Unfortunately, in today’s society, we are constantly overstressed and under recovered, which keeps our ANS out of balance. The over-stimulation of the ANS keeps our body in a constant state of at flight or fight. It increases our blood pressure, elevates the heart rate, dilates the pupils, slows digestion, and increase blood glucose levels.
Conversely, the PNS is not stimulates enough, preventing adequate recovery from stress, whether that stress is mental, emotional, physical or environmental. You can probably see how this state of ANS activation, and PNS depression can cause some serious issues to your metabolism and health.
Use HRV to Monitor Stress and Manage Training
HRV looks at the variability of heart rate at the same time of day, under the same conditions to identify recovery ability of the body. The more variation in HR signifies more PNS activation. The less variation, the more ANS stimulation.
By measuring your Heart Rate Variability daily, you can assess how well your body is adjusting to the stress you are experiencing everyday. And not just the stress from exercise. Yes exercise is a stress, albeit in most cases it is a good stress that can create some excellent adaptations that benefit your health, it is still a stressor and can cause issues if done incorrectly. Your body doesn’t differentiate from the type of stress, it just responds.
Knowing this, if your HRV is low, your body has too much SNS activation. That means that your body is not recovering well from whatever stress is being placed on it. In this case you would benefit from modifying your training to prevent adding more stress on your already under-recovering body.
Conversely, if your HRV is high, then you are recovering adequately, and can therefore train at high intensities without worrying about overstressing your body.
HRV allows for daily modification of your workout intensity to ensure that you are getting optimal results without causing undue stress and under-recovery.