Large Intestine 4 (LI 4, He Gu), aka, “that point that always hurts”.
There are many important points along the Large Intestine channel, but the one I want to highlight here is LI 4. This point is located on the dorsum of one’s hand, in the web space between the thumb and index finger. If you are palpating it now you may notice its tenderness. This is a very powerful point. Traditionally it is used for a long list of indications, especially for the head, face, digestion, and overall body pain.
Scientifically LI 4 has been shown to have a relatively high electrical conductance field when compared with other acupuncture points. A 1976 study published in Psychoenergetic Systems found in general that acupuncture points and meridians maintain electrophysiological conductance patterns when compared to areas of the body where there is an absence of an acupuncture point, and therefore a meridian. This very potential of electrical conductivity may be part of the explanation Western science desires in order to understand the mystery behind acupuncture’s mechanism of action. More importantly, this may also explain to patients, and practitioners, why LI 4 is indeed often so darn tender.
 Becker RO, Reichmanis M, Marino AA, and Spadaro JA. (1976). Electrophysiological Correlates of Acupuncture Points and Meridians. Psychoenergetic Systems. 1: 105-112.