Yoga practices (postures, chanting, breathing exercises, and meditation) are beneficial for many diverse, frequently comorbid medical conditions – from depression, epilepsy, post-traumatic stress disorder (PTSD) to chronic pain. But how can it be that “one thing” is beneficial for so many different problems?

Streeter, Gerbarg, Saper, Ciraulo, and Brown (2012) theorize that a reduction of psycho-physiological load in the stress response system through yoga practices leads to the restoration of optimal homeostasis (ability to maintain a relatively stable internal state that persists despite changes in the world outside). Due to repeated or chronic stress the vehicle of the spirit (mind and body) is endangered to get out of balance. In a healthy stress response, the body gets out of balance only for a relatively short period of time. However, when the perceived stressful situation is repeatedly experienced over a certain period of time, the body cannot compensate for this accumulating wear and tear (allostatic load) and will respond with an imbalance of the autonomic nervous system (ANS), which has a wide range of effects. It is is associated with the increase of symptoms in (or even discussed as the source of): depression, anxiety, PTSD, alcohol dependence, epilepsy, chronic pain, cardiovascular disorders, diabetes, obesity, immune infectious diseases, cancer, and asthma.

There are different pathways in the neural regulation of the ANS, which were described by Porges (2001) in his influential polyvagal theory. The developmentally oldest pathway is the unmyelinated visceral vagus nerve, which responds to threat by depressing metabolic activity (freeze reaction). The sympathetic nervous system (SNS) as the next developmental pathway reacts by mobilization (flight and fight). The most advanced, myelinated vagus pathway supports calm states consistent with the metabolic demands of growth, repair, and restoration. Found only in mammals, it promotes social engagement and proliferates feelings of safety. Myelinated vagal efferent fibers serve as the “vagal brake” that enables rapid control of heart rate (HR). This more rapid control of the HR allows for a greater HR variability (HRV) than the slower acting SNS, which is a crucial indicator for the general health status and even is a predictor of morbidity. Thus, a high HRV implicates a greater flexibility of the stress response system to respond to challenges and implies an increased activity of the parasympathetic nervous system (PNS). This flexibility enables the body to more quickly return to a calm, resting, reparative and anti-inflammatory state when the threat has ceased.

However, when stability is maintained through allostasis (when the body needs to compensate), the flexibility of the system is decreased. The greater dependence on the sympathetic excitation furthers hypertension, hyperarousal, and over reactivity, and makes the system prone to pathological states and damage to the organism. Medical conditions, such as depression, PTSD, epilepsy, and chronic pain go along with a PNS underactivity, a decreased HRV as well as with an increased cortisol level (an indication of a high stress level). Different studies on yoga practices (breathing exercises, hatha yoga, or meditation) showed that they can increase the HRV as well as lower the cortisol level, which both indicate the increase of PNS activity. Streeter and colleagues conclude that yoga practices lead to a reduction of the allostatic load and thereby to an increase in the activity of the third pathway with an increase of the PNS.

In sum, the severity, frequency and length of the stressful events as well as the individual resiliency to stress determine the balance of the spirit’s vehicle. No matter what the source of the imbalance of the ANS might be, yoga practices are likely to decrease the symptoms of the given medical condition by supporting calm and restorative states.

Recommended further reading

• Porges, S. W., 2011. The Polyvagal Theory: Neurophysiological Foundations of Emotions, Attachment, Communication, and Self-regulation. New York, NY: W. W. Norton & Company.
• Van der Kolk, B., 2015. The Body Keeps the Score: Brain, Mind, and Body in the Healing of Trauma. New York, NY: Penguin Books.

Main references

• Porges S. W. (2001). The polyvagal theory: phylogenetic substrates of a social nervous system. Int J Psychophysiol, 42, 123–46.
• Streeter, C. C., Gerbarg, P. L., Saper, R. B., Ciraulo, D. A., & Brown, R. P. (2012). Effects of yoga on the autonomic nervous system, gamma-aminobutyric-acid, and allostasis in epilepsy, depression, and post-traumatic stress disorder. Medical Hypotheses, 78(5), 571-579.