What happens during Shavasana?

This section provides an opportunity to share scientific articles and studies that shine some light on how Yin Yoga affects us. When you post a link to a study or article here, please include one or two paragraphs summarizing the important findings and/or provide the salient quotation from the article. Please do not simply cut and paste the whole study: provide only links and your summary.
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What happens during Shavasana?

Post by Bernie »

I was recently asked the following question, "What happens during Shavasana?" Wow! This is a big topic. There are so many ways to address the question. What follows are my first thoughts....enjoy!

  • “Lying down on the ground, like a corpse, is called Shavasana. It removes fatigue and gives rest to the mind.”
    I-34 Hatha Yoga Pradipika (page 6 of version by Pancham Sinh)

    “Lying flat on the ground with the face upwards, in the manner of a dead body, is Shavasana. It removes tiredness and enables the mind (and whole body) to relax.”
    I-32 Hatha Yoga Pradipika (page 98 of version by Swami Muktibodhananda)

    Shavasana (also called Mrtasana): Shava means corpse: Mrta means death. The object is to imitate a corpse. A corpse is still with no movement of the mind or body. Stillness of the body is easy. Stillness of the mind is difficult. Therefore this is one of the hardest postures to master.
    Paraphrased from B.K.S. Iyengar Light on Yoga (page 423)

    According to Swami Muktibodhananda, the Hatha yogis borrowed Shavasana from the Tantric version where the tantrika sat on a corpse and practiced his mantra. Body and mind relax, but the mind remains focused to keep it from wandering. It is used to relax the body and develop body-awareness and pratyahara. It should be practiced between asanas and after a hectic day.
From these above definitions it is clear that Shavasana was not meant as just a bodily relaxation; it was mind-training meditation as well. That is not necessarily the way it is taught today. Often modern yoga teachers will allow students to let their minds drift away, or even go to sleep. Thus the answer to the question, “what happens during Shavasana?” really depends upon the way it is being practiced.

Physiological effects of shavasana

In all styles, Shavasana offers a rest for the physical body. During this rest period several things can occur. If the body has been subjected to a lot of strain (elongation of the tissues) a process called creep can occur. It takes time for this lengthening to reverse and for the tissues to return to their original stiffness. Shavasana may provide enough time for the creep to fully dissipate. {1} It is also theorized that the state of water in our fascia may undergo a change, from gel (solid) to sol (liquid). {2} In the sol state, toxins and free radicals that may have been trapped in the gel are released and can flow into the lymph system for elimination. But once this detoxification is complete, we need some time for the water to return to the gel state. Shavasana provides some of this time.

If the yoga asana practice has been quite aerobic and the heart rate and breathing rate were elevated, Shavasana allows time for them to return to their resting rates. If the muscles were warmed up during the practice, they can begin to cool down as well.

According to Stuart McGill, after a bout of exercise, the body needs a refractory period in which the tissues that were used become more usable. He calls this the “biological tipping point.” If we deprive ourselves of the rest period after stressing the body, the body does not regenerate fully and is weaker for the next bout of exercise. Thus, the relaxation or rest or Shavasana period is just as important for optimal health as the exercise or stress period. {3}

Energetic effects of Shavasana

The ancient yogic texts discuss the energetic effects of yoga on the flow of prana through the nadis, specifically the ida (left, moon, yin, feminine channel), pingala (right, sun, yang, masculine channel) and the sushumna nadis. While there is no proven correlation between the ida and pingala nadis to the parasympathetic nervous system (PNS—the rest and digest function) and sympathetic nervous system (SNS—the fight or flight function), there certainly seems to be some similarities. While Shavasana is thought to balance the flow of prana through the nadis, there are studies that show Shavasana increases activation of the PNS while reducing activation of the SNS. {4}

Another noted effect of Shavasana, especially after yoga asana practice, is the calming of breath rate, reduced oxygen consumption and increased breath volume. {5} Heart rate variability (HRV) is one measure of heart health, with a higher rate indicating greater health than a lower rate. Shavasana has been shown to improve HRV and thus promote cardiovascular health. {6}

Psycho-emotional effects of Shavasana

Beyond the physical and energetic benefits of Shavasana, the meditative aspects of the practice have also been found to provide psycho-emotional benefits. However, it is difficult to determine whether the benefits are due to the asana practices or to the ending Shavasana practice or a combination of both. When Shavasana includes a mindfulness or meditative aspect as described in the earliest text cited above, rather than a letting the mind wander where it will, we can ascribe the known benefits of meditation to Shavasana as well. And, certainly there is an affect (emotional effect) that occurs when the PNS is activated. A reduction in anxiety and increase in calmness has been noticed by several researchers. {7}

As mentioned at the beginning, there are different approaches to Shavasana. One can use the practice as a chance to develop mindfulness and meditative awareness, or to let go fully and deeply relax the mind and body. These are very different practices which can lead to very different benefits, as noted in the following study:
  • The intention of mindfulness and relaxation practices differ ... The goal of mindfulness practices in clinical settings is to build awareness and acceptance skills in order to tolerate discomfort, gain distance from unhelpful thoughts, and ultimately make adaptive behavioral choices to reduce suffering and pursue valued goals—even while uncomfortable emotions or physical sensations may be present. The goal of relaxation practices is to elicit the [relaxation response] to directly reduce physiological and psychological stress, decrease physical tension, and increase a sense of calm in order to promote positive health behaviors and outcomes. In short, mindfulness practices teach acceptance of present moment internal events, while relaxation practices teach strategies to change internal events. {8}
Depending upon the style of Shavasana you are practicing your may acquire the mindfulness benefits, or you may acquire the relaxation response benefits. But, you are unlikely to get both during the same Shavasana.

Final thoughts

So, what is really going on during Shavasana? It depends! It depends upon the style of Shavasana being practiced, but it also depends upon the person doing the practice and the events that preceded the practice. There is naturally a lot of human variability and some people will gain certain benefits while different people will gain other benefits. What is important is – what benefits do YOU get from your Shavasana sessions? Are you getting what you desire, what you need and what you intend? If not, you can vary the way you are practicing Shavasana. Start with your intention, pay attention, and if you are not achieving your goal, feel free to modify your practice.

{1} Of course, this depends upon how much creep has occurred and how long the Shavasana lasts.
{2} The process of changing the state of water from gel to sol is called thixotropy. Robert Schleip describes this process in his article Fascial plasticity – a new neurobiological explanation.
{3} See Stuart McGill’s video presentation The Search for the Biological Tipping Point.
{4} “Shavasana has been found to reduce physiological arousal,[19] and to be effective in helping practitioners cope with stress manifestations, for example, Bera et al. found recovery from induced physiological stress was significantly faster for supine posture with additional progressive relaxation, compared to resting, sitting in a chair, or plain shavasana (SR).[20] In another study, a significant decrease in breath rate was noted after performance of the yoga-based Isometric Relaxation Technique (IRT), when compared to SR.[21]” From Pradhan B, Nagendra HR. Effect of yoga relaxation techniques on performance of digit-letter substitution task by teenagers. Int J Yoga. 2009;2(1):30-34. doi:10.4103/0973-6131.43293.
{5} “There was a significant decrease in the amount of oxygen consumed and in breath rate and an increase in breath volume after both types of sessions (2-factor ANOVA, paired t test). However, the magnitude of change on all 3 measures was greater after CM: (1) Oxygen consumption decreased 32.1% after CM compared with 10.1% after SH; (2) breath rate decreased 18.0% after CM [cyclic meditation = calming and stimulating measures] and 15.2% after SH; and (3) breath volume increased 28.8% after CM and 15.9% after SH. These results support the idea that a combination of yoga postures interspersed with relaxation reduces arousal more than relaxation alone does.” From Telles S, Reddy SK, Nagendra HR. Oxygen consumption and respiration following two yoga relaxation techniques. Appl Psychophysiol Biofeedback. 2000 Dec;25(4):221-7. doi: 10.1023/a:1026454804927. PMID: 11218923.
{6} “Short-term practice of relaxation therapy can improve autonomic balance and promote cardiovascular health of medical students.” From Pal GK, Ganesh V, Karthik S, Nanda N, Pal P. The effects of short-term relaxation therapy on indices of heart rate variability and blood pressure in young adults. Am J Health Promot. 2014 Sep-Oct;29(1):23-8. doi: 10.4278/ajhp.130131-QUAN-52. Epub 2013 Nov 7. PMID: 24200249.
{7} See Subramanya P, Telles S. Effect of two yoga-based relaxation techniques on memory scores and state anxiety. Biopsychosoc Med. 2009;3:8. Published 2009 Aug 13. doi:10.1186/1751-0759-3-8.
{8} From Luberto CM, Hall DL, Park ER, Haramati A, Cotton S. A Perspective on the Similarities and Differences Between Mindfulness and Relaxation. Glob Adv Health Med. 2020;9:2164956120905597. Published 2020 Feb 5. doi:10.1177/2164956120905597
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