“Engage your abdominals, draw your low belly in, and harden through the midline.” These are familiar cues to yogis and those practicing any type of physical activity, from cycling to weight lifting to dance. Being mindful of abdominal engagement is important in many movements because it helps stabilize the spine and prevent “dumping” into the low back or lumbar spine. Nonetheless, we walk a fine line in terms of creating a culture that overemphasizes abdominal engagement and strength. True, many of us spend the majority of our day sitting at a desk, not thinking about contracting the abdomen, so we do need to create an active practice of abdominal strengthening exercises. But as with most aspects of life, in order to maintain health we must engage in balancing or opposing practices as well. By actively focusing on softening the abdomen, we are giving our immune and nervous systems the chance to take the spotlight and function at maximum capacity as well.
Functionally, the nervous system is divided into two main branches: the somatic (responsible for voluntary actions, such as 
lifting your arm) and the autonomic (responsible for involuntary actions, such as digestion and dilation of the pupil). While many are familiar with two branches of the autonomic nervous system, the sympathetic (commonly associated with the “fight or flight” response) and the parasympathetic (or the “rest and digest”) systems, there is a third branch of the autonomic nervous system, called the enteric nervous system (ENS). The ENS lies in the abdominal, or visceral, cavity and acts in coordination with both the sympathetic and parasympathetic branches. It also has the ability to stand alone, harboring intrinsic reflexes that can operate without input from the brain, central nervous system, and autonomic nervous system.
This unique, independent nature sets the ENS apart from other branches of the nervous system and therefore it is often classified as a completely separate system. While the ENS is often understated, its importance is profound. The ENS is intricately connected to our physical and emotional well-being. It is interspersed throughout our entire gastrointestinal (GI) tract; contains more than 100 million neurons (five times the number found in the spinal cord); produces more than 80 percent of the body’s supply of serotonin (a broad acting neurotransmitter influencing mood, appetite, the endocrine system, and cardiovascular system); and 50 percent of the body’s dopamine supply (a neurotransmitter associated with feelings of motivation and happiness).Due to the interconnected nature of the ENS, it is often referred to as our “belly brain” and is responsible for “gut feelings” and “butterfly” sensations in the abdomen.
Problems arise when the ENS is overworked and not given a chance to restore. In our hectic, over-stimulated lives, we can overactivate this system both locally and peripherally. Locally, the GI tract has receptors that translate chemical and mechanical stimuli into enteric neuron activation. While many of us may not be aware of it, most people store tension in their abdomen. Granted, while we might not be actively contracting our obliques and rectus abdominus (our “6-pack muscle”), it is likely we are holding a deep, subtle contraction in the tissues of our abdomen in response to daily stressors. By simply placing your hand over your belly and focusing on breathing and softening, you will likely notice a change in the pressure and firmness of your abdomen. Overengagement, or too much “clenching,” in the abdominal region causes a restriction of blood flow to the organs of the visceral cavity, limiting nutrient delivery and waste removal. Without continuous, fluid blood flow, there is a local build up of chemical messengers, which can exacerbate the issue by generating a feedback signal for our visceral cavity to contract further. When this environment persists, it can lead to chronic pain, digestive distress, and imbalance in hormonal and neural signals.
Peripheral stimuli can also affect abdominal tension. In day-to-day life, we encounter various stressors, all of which initiate chemical responses in our bodies. Stress, while actually beneficial in small doses, creates a problem when it is chronic and not managed properly. It causes a central release of certain hormones and immunological factors, such as the corticotropin-releasing hormones, IL-6 and IL-8, which then circulate throughout the body, initiating stress responses in various tissues. A recent study revealed that elevation of these three factors caused a change in the expression of structural proteins in the GI tract, leading to visceral pain and irritable bowel syndrome. In addition, these stress hormones have been shown to directly stimulate neurons of the enteric nervous system, which then initiate the aforementioned “clenching.”
How exactly can we help our ENS through yoga? One simple way is to practice slow, deep, abdominal breathing. Since the ENS works in concert with the other branches of the autonomic nervous system, when we activate the parasympathetic nervous system through controlled breath we also initiate a relaxation response in the ENS. Countless studies have also shown that deep breathing can shift your biochemistry by affecting the levels of stress hormones in our bodies, which has an indirect impact on the ENS by decreasing the stimulatory load on the receptors connected with the ENS. Finally, besides the internal, mechanical influence the rhythmic contraction of the diaphragm has on the ENS, we can also initiate an external, mechanical, relaxation response by laying the abdomen over a bolster or rolled up blanket. By placing external pressure on the abdomen and relaxing abdominal contraction, we force ourselves to release the subtle clench that is chronically maintained in the visceral cavity. This allows for unhindered blood flow, which, in turn, allows nutrients to access the abdomen, removes waste, and causes those mood-boosting hormones, serotonin and dopamine, to start circulating throughout the body.
So don’t be afraid to soften your belly periodically. Your body and mind will thank you.
Physiology of Yoga 