If you've ever unrolled your yoga mat a total stress case and left class wearing a serene smile on your face, you've felt yoga's ability to reset your nervous system. That post-yoga calm is the handiwork of your parasympathetic nervous system, often dubbed the "rest and digest" system. Many of yoga's health benefits stem from its ability to turn up the dial on the parasympathetic system.
The Autonomic Nervous System
The autonomic nervous system is in charge of unconscious bodily functions, such as heart rate, blood pressure and digestion. It's split into two parts: the sympathetic and parasympathetic divisions. The sympathetic system kicks in when you're under stress -- your heart rate and blood pressure shoot up, your breathing accelerates and your digestion grinds to a halt. Often called the "rest and digest" system, the parasympathetic division turns off the stress response, returning your heart rate, breathing and blood pressure to normal.
The Stress Response
For your cavewoman ancestors, stress likely meant an immediate physical threat. The sympathetic nervous system is well-suited to respond to short-term emergencies, hence its nickname, the "fight or flight" system. Today, however, you may be faced with stressful situations that are not so quickly resolved: conflicts with your boss, financial worries, even traffic jams. When stress becomes a way of life, your sympathetic nervous system doesn't get the rest it should, which can contribute to health problems like diabetes, depression, autoimmune diseases, heart attacks and strokes.
By turning off the sympathetic system and turning on the parasympathetic, yoga gives your heart and circulatory system a break. Yoga practice lowers your heart rate and blood pressure. It improves heart rate variability, a marker of cardiovascular health and a sign of increased parasympathetic activity. Stress plays a role in insulin resistance and diabetes -- another risk factor for heart disease. Yoga lowers blood glucose levels and reduces your risk of diabetes.
Yoga has been shown to alleviate job stress, anxiety, depression and insomnia. It can help with migraine headaches, as well. There are several theories about how yoga exerts its calming influence on the parasympathetic system. Some researchers point to yoga's emphasis on slow, deep breathing, which stimulates the parasympathetic system. Others credit its focus on mindfulness and re-training the brain. Yoga poses that massage your body and relax your muscles also help stimulate the parasympathetic system.
- "The Science of Yoga"; William J. Broad
- "Yoga as Medicine"; Timothy McCall
- The Journal of Alternative and Complementary Medicine: The Health Benefits of Yoga and Exercise: A Review of Comparison Studies; Alyson Ross and Sue Thomas
- Evidence Based Complementary and Alternative Medicine: Iyengar Yoga Increases Cardiac Parasympathetic Nervous Modulation Among Healthy Yoga Practitioners; Kerstin Khattab et al.
- Complementary Therapies in Clinical Practice: Yoga Clinical Research Review; Tiffany Field
- Medical Hypotheses: Physiology of Long Pranayamic Breathing: Neural Respiratory Elements May Provide a Mechanism That Explains How Slow Deep Breathing Shifts the Autonomic Nervous System; Ravinder Jerath, et al.
- Journal of the American Board of Family Practitioners: Risk Indices Associated with the Insulin Resistance Syndrome, Cardiovascular Disease, and Possible Protection with Yoga: A Systematic Review; Kim E. Innes et al.
Joe Miller started writing professionally in 1991. He specializes in writing about health and fitness and has written for "Fit Yoga" magazine and the New York Times City Room blog. He holds a master's degree in applied physiology from Columbia University, Teacher's College.