Excerpt from article: “The parasympathetic nervous system is the sweet sister of the sympathetic nervous system. It takes us into the rest-and-digest mode. This is the path to deep rejuvenation for the body, mind, and soul. Relaxation is the yin to our fitness efforts’ yang”.
http://breakingmuscle.com/health-medicine/the-vagus-nerve-an-unexpected-key-to-better-performance