BL40 (Weizhong, “Weizhong”) is the He-Sea Point point of the Bladder Meridian. It is located at the midpoint of the transverse popliteal crease, in the depression between the tendons of biceps femoris and semitendinosus. The point is best located with the knee slightly flexed. It benefits the lumbar spine and knees, clears heat and cools the blood, dispels blood stasis, resolves dampness, and alleviates pain.
At the midpoint of the transverse popliteal crease, in the depression between the tendons of biceps femoris and semitendinosus. The point is best located with the knee slightly flexed.
Perpendicular insertion 1.0 to 1.5 cun, or prick the popliteal vein to cause bleeding. Avoid deep insertion to prevent injury to the popliteal artery and nerve.
Benefits the lumbar spine and knees, clears heat and cools the blood, dispels blood stasis, resolves dampness, and alleviates pain.
Lumbar pain, lumbar pain radiating up the spine to the head, heavy and painful conditions of the lumbar region and legs, chronic stubborn rashes, genital twitching, urinary incontinence, difficult urination, tight sinews, epilepsy with opisthotonos, heat illness with lack of sweating, hot feet with reversal, inability to bend or extend the knee, lower abdominal fullness, urinary retention, hemorrhoids, pain in the perineal region, leprosy with loss of eyebrows, fever, lumbar and spinal pain, lower back heaviness and inability to lift the body, wind-damp impediment (Bi syndrome), pain in the hip joint, heat in the four limbs during febrile disease, bladder diseases, lower back pain like it is broken, inability to bend the hip, popliteal fossa feeling knotted, calf feeling like it's being torn apart, pain in the neck, back, lumbar, sacrum, popliteal fossa, calf, and foot, urinary retention with lower abdominal distention, pain in the knee and big toe, lumbar and spinal pain with a heavy, sinking sensation.
Weizhong is a primary point for acute and chronic lumbar pain, sciatica, and knee disorders, famously summarized by the saying 'for lumbar and back problems, seek Weizhong.' The classical texts emphasize bloodletting this point, especially for heat conditions, chronic skin diseases, and severe pain along the Bladder channel. Its function as the Bladder's Lower He-Sea point also makes it effective for urinary disorders like retention and incontinence.
Classical text; the translation was prepared with AI and is not clinical advice.
《類經圖翼》 Lèijīng Túyì — Illustrated Wings to the Classified Canon, Zhang Jiebin, 1624 · 卷七 · 經絡（五） · 足太陽膀胱經穴 · Source: jicheng.tw ↗
委中（一名血郄） 在膕中央約文動脈陷中，伏臥屈足取之It is located in the depression with a pulsing artery at the centre of the crease at the back of the knee, according to this text; BL40, also called Xuexi, is found lying prone with the leg bent.
《針方六集》 Zhēnfāng Liùjí — Six Collections on Needling, Wu Kun, 1618 · 卷之六·兼羅集 · 脊膂強痛十七 · Source: jicheng.tw ↗
委中，穴在兩膝後膕中橫紋內。 針入一寸，單瀉。 禁灸。 四畔紫脈上皆可用三稜針出血，絕妙According to this text, BL40 lies in the transverse crease at the back of each knee; it is needled 1 cun with draining only, moxibustion is forbidden, and the purple vessels around it may be bled with a three-edged needle, which the text praises highly.
《針灸逢源》 Zhēnjiǔ Féngyuán — Sources of Acupuncture & Moxibustion, Li Xuechuan, 1815 · 卷四 · 經穴考正 · 足太陽膀胱經穴考 · Source: jicheng.tw ↗
委中（一名血郄） 在膕中央約紋動脈陷中伏臥取之膀胱脈所入為合。 （針五分。 禁灸）治熱病汗不出According to this text, BL40 (also called Xuexi) lies in the pulsing depression at the centre of the knee crease, found lying prone, and is the he-sea point where the bladder channel enters; needle 5 fen, moxa forbidden, and it was used for febrile disease without sweating.
《針經指南》 Zhēnjīng Zhǐnán — Guide to the Needling Classic, Dou Hanqing, 1295 · 流注通玄指要賦 · Source: jicheng.tw ↗
腰腳疼，在委中而已矣The text records that for pain of the lower back and legs, BL40 is the point to use.
BL40 is one of 67 points on the Bladder Meridian. Nearby points:
BL40 (Weizhong) is located at the midpoint of the transverse popliteal crease, in the depression between the tendons of biceps femoris and semitendinosus. The point is best located with the knee slightly flexed.
BL40 benefits the lumbar spine and knees, clears heat and cools the blood, dispels blood stasis, resolves dampness, and alleviates pain. Common clinical indications include lumbar pain, lumbar pain radiating up the spine to the head, heavy and painful conditions of the lumbar region and legs, chronic stubborn rashes, genital twitching, urinary incontinence, difficult urination, tight sinews, epilepsy with opisthotonos, heat illness with lack of sweating, hot feet with reversal, inability to bend or extend the knee, lower abdominal fullness, urinary retention, hemorrhoids, pain in the perineal region, leprosy with loss of eyebrows, fever, lumbar and spinal pain, lower back heaviness and inability to lift the body, wind-damp impediment (Bi syndrome), pain in the hip joint, heat in the four limbs during febrile disease, bladder diseases, lower back pain like it is broken, inability to bend the hip, popliteal fossa feeling knotted, calf feeling like it's being torn apart, pain in the neck, back, lumbar, sacrum, popliteal fossa, calf, and foot, urinary retention with lower abdominal distention, pain in the knee and big toe, lumbar and spinal pain with a heavy, sinking sensation.
Perpendicular insertion 1.0 to 1.5 cun, or prick the popliteal vein to cause bleeding. Avoid deep insertion to prevent injury to the popliteal artery and nerve. Caution: The Zhen Jiu Ju Ying warns: 'Puncturing the large vessel in the center can cause a person to collapse and lose color.' This refers to the popliteal artery.
BL40 is a point on the Bladder Meridian (Zú Tài Yáng Páng Guāng Jīng).