By: Jesse Russell
Just about anyone that practices yoga can attest to the fact that they feel better and more relaxed after they practice. This is not merely subjective, and there’s a good amount of science to support this notion. Much of our body’s ability to regulate itself and maintain its health is related to what is known as the Autonomic Nervous System (ANS). This is a binary system comprised of the Sympathetic Nervous System (SNS) and the Parasympathetic Nervous System (PNS). In order to understand yoga’s beneficial effects on the body, it is important to have a general understanding of how these two systems operate. Understanding the binary nature of these systems is really quite simple – when one turns on the other turns off and vice versa (although it’s not exactly all or none).
The SNS is often referred to as our “fight or flight” response. This system is necessary for our bodies to be able to respond to a threat and to escape from immediate danger. In order to do so, it directs the flow of blood and oxygen towards the limbs. The result is an increase in heart rate and blood pressure as well as a rise in blood sugar levels. Stress hormones such as adrenaline and cortisol are released by the body as it prepares to battle or to flee to safety. This is a vital necessity for our survival, but if the SNS is overly active the body has no time to recover, and it becomes prone to disease both physically and mentally.
When the SNS is at rest, the PNS becomes active. Commonly referred to as the “rest and digest” mode, when the PNS is active blood and oxygen are able to flow back towards the intestines and internal organs. Just as the SNS increased certain factors such as heart rate, blood pressure, and blood sugar levels, when the PNS is active the body displays a decrease in these three factors. The PNS also enables the body to recover from stress and allows the muscles to recover. It is imperative that the body is able to rest and recover following a stressful situation, or, as mentioned above, it becomes prone to physical and mental disease and/or injury.
Many of the practices in yoga (such as deep breathing, slow movements, and meditation) help to activate the PNS and bring the body back to homeostasis. Vigorous asana practices and breathing techniques actually activate the SNS, but if these practices are concluded with relaxing poses and easeful breathing (such as shavasana), there is evidence showing that this leads to even deeper relaxation (this is why we should never skip out on shavasana). Just like anything, the more we practice the more we train our bodies to respond to stress and maintain an equilibrium. When the body is balanced, the mind is able to be at ease, and we are capable of warding off disease.