We’ve all heard of the “fight or flight” response, where the heart races, breath accelerates, and adrenaline floods our muscles. The “rest and digest” response is its opposite number. When we assume the “rest and digest” response our respiratory, circulatory, and other systems slow down. We prepare to absorb rather than fight or flee what’s coming at us.
The parasympathetic nervous system is in charge of resting and digesting. As William Broad points out in his recent book The Science of Yoga, yoga trains the parasympathetic nervous system, and this is one of its distinctive strengths as a program of health.
Of all the poses, shoulderstand is one that allows the parasympathetic nervous system to sing the most beautifully. Here’s why.
Shoulderstand causes our heart rate and blood pressure to drop.
Lowered heart rate and blood pressure are signatures of the parasympathetic nervous system. Shoulderstand may trigger them in two ways, thus jump-starting the parasympathetic nervous system into action.
- When the legs are above the head, gravity helps blood to return to the heart, which then becomes more full than otherwise. Since more blood is pumped with each stroke, the heart doesn’t need to pump as much or as fast. So it pumps slower and softer. (This effect would also be present in headstand.)
- Unlike headstand, shoulderstand presses the back of the neck, which bears much of the weight of the body. It also creates pressure in the front of the neck as the chin sinks into the notch above the sternum. Sensors in the large arteries of the neck perceive the pressure but may misinterpret it as a signal of pressure in the the brain and sinuses. To attempt to restore equilibrium, the heart would beat slower and softer.
Besides lowering blood pressure and heart rate, shoulderstand may stimulate the parasympathetic nervous system in other ways
- The pressure on the neck may affect the vagus nerve as it passes through the neck. 80% of the nerve fibers concerned with the “relaxation response” are contained in this wandering nerve. (Vagus comes from the same Latin root as vagabond and vagrant; it meanders all over the torso.)
- There are an extraordinary number of muscle spindles at the back of the neck. Stretching and placing pressure on them may activate these muscle spindles, causing a parasympathetic nervous response in the same way as a backrub does.
- It is interesting to note that the neck position of shoulderstand, (known as jalandhara bandha) also features in most classic pranayama techniques, which also have a deeply calming effect.
- The position of the neck holds the head such that the gaze of the eyes naturally falls on the torso and legs. Only with difficulty are we able to observe anything other than our own physical self. This naturally turns the attention inward, making shoulder stand an ideal posture for self-examination