BL-39 (Wei Yang) Bend Yang

What does BL-39 Wei Yang do?

Wei Yang BL-39 lies on the Bladder channel but functions as the Lower He-Sea point of the San Jiao — and that single classification explains almost everything the point is used for. The San Jiao is described in the classics as the organ that governs the passage of fluids through the body, so its Lower He-Sea point is the place the tradition treats when fluids will not move: urine that will not come, oedema, a lower abdomen that feels full and tight. This is one of the genuinely confusing points in the canon, because its channel and its function belong to two different organs, and a reference has to say so plainly rather than let the reader assume the Bladder.

• Harmonises the San Jiao and regulates urination — the primary action recorded in Sacred Lotus sources & references, and the reason a point behind the knee carries urinary and oedema indications. It is the classical distal point for difficult urination, retention of urine and generalised water swelling.
• Relieves fullness and distension of the lower abdomen — the fluid and qi congestion of the lower burner, recorded alongside the urinary indications and understood as the same disorder seen from the abdomen rather than the bladder.
• Activates the channel and alleviates pain — the second recorded action, and a local and channel effect: stiffness and pain of the lower back, cramp and spasm of the leg and foot, and pain and restriction at the back of the knee.

The two halves of the point sit oddly together until the classification is understood. The back-and-leg indications come from where BL-39 is — near the end of a channel that runs the whole length of the spine. The urinary and abdominal indications come from what BL-39 is — the lower entry point of the San Jiao.

Source: Sacred Lotus sources & references (channel, category and the recorded actions above); Deadman & Al-Khafaji, A Manual of Acupuncture, p. 298; Chinese Acupuncture & Moxibustion, p. 184; Ling Shu, on the Lower He-Sea points; cross-referenced against multiple online sources.

What is BL-39 Wei Yang used for?

Wei Yang BL-39 is used above all for difficult urination and for oedema — the fluid disorders the tradition assigns to the San Jiao — and secondarily for stiffness and pain of the lower back and cramp in the leg. The indications recorded in our sources are listed below. They describe traditional use, not proven treatment, and this point sits in the popliteal fossa, so the needling record below should be read alongside them.

• Difficult or scanty urination
• Retention of urine
• Oedema and generalised water swelling
• Distension and fullness of the lower abdomen
• Stiffness and pain of the lower back
• Cramp and spasm of the leg and foot
• Pain and stiffness at the back of the knee

Source: Sacred Lotus sources & references (existing indication record); Chinese Acupuncture & Moxibustion, p. 184; Deadman & Al-Khafaji, A Manual of Acupuncture, p. 298.

Where is BL-39 Wei Yang, and how is it used in practice?

Wei Yang sits in the crease behind the knee, toward its outer end — in the small hollow on the inner side of the strong tendon that stands out at the outer corner of the crease when the knee is bent against resistance. That tendon is biceps femoris. BL-40 Wei Zhong lies in the middle of the very same crease, roughly a thumb's width to the inner side, so the two points are found in one movement and are directly comparable. The whole hollow they share is the popliteal fossa, which is why the needling record for this region is more detailed than for most limb points.

Which points is BL-39 combined with?

• With BL-22 San Jiao Shu and REN-05 Shi Men — the most instructive combination on the page, because it assembles the three classical points of one organ: BL-22 is the Back Shu of the San Jiao, REN-05 its Front Mu, and BL-39 its Lower He-Sea point. Sacred Lotus sources & references confirm all three designations by query. Few organs allow that complete a set, and it is the clearest demonstration of what the Lower He-Sea classification is for.
• With REN-03 Zhong Ji and BL-28 Pang Guang Shu — the standard combination for urinary difficulty and retention, joining the Front Mu and Back Shu of the Bladder to the distal fluid point. All three are held here.
• With SP-09 Yin Ling Quan — the He-Sea and Water point of the Spleen and the tradition's other great point for water accumulation, paired with BL-39 for oedema and for a heavy, swollen lower body.
• With BL-40 Wei Zhong — its immediate neighbour in the same crease, added for the lumbar and leg indications, where BL-40 is much the stronger of the two.
• With BL-23 Shen Shu — for the urinary and lower-back presentations together, joining the Back Shu of the Kidneys to the distal point.
• With BL-38 Fu Xi — the point just above it on the same lateral line of the fossa, and its nearest neighbour on the channel; both are held here.

Where does BL-39 sit among the Lower He-Sea points?

The six Lower He-Sea points are the classical scheme that puts one point below the knee for each of the six fu organs, and BL-39 is the San Jiao's. The Ling Shu sets out the principle that the fu organs are governed from the three yang channels of the leg, and the resulting set is:

• Stomach — ST-36 Zu San Li. Our ST-36 record states this explicitly, and ST-36 is unusual in being both the Stomach channel's own He-Sea point and the Stomach's Lower He-Sea point.
• Large Intestine — ST-37 Shang Ju Xu, on the Stomach channel of the leg rather than on its own arm channel.
• Small Intestine — ST-39 Xia Ju Xu, likewise on the Stomach channel.
• Gallbladder — GB-34 Yang Ling Quan, which is also the channel's own He-Sea point and the Hui-Meeting point of the sinews.
• Bladder — BL-40 Wei Zhong, also the channel's own He-Sea point.
• San Jiao — BL-39 Wei Yang, borrowed onto the Bladder channel.

All six of those points are held in this library, confirmed by query. The pattern to notice is that the three fu organs whose channels run on the arm — Large Intestine, Small Intestine and San Jiao — have no He-Sea point on the leg of their own, so the classics assign each one a borrowed point on a leg yang channel. BL-39 is the only one of the three borrowed onto the Bladder channel rather than the Stomach, and it is the only point in the whole scheme whose Lower He-Sea designation is carried explicitly in our own point categories.

Source: Sacred Lotus sources & references (location, categories and cross-referenced point records — the six points, the Back Shu and Front Mu of the San Jiao and the ST-36 statement were all confirmed by query, not from memory); Ling Shu, on the Lower He-Sea points of the six fu; Deadman & Al-Khafaji, A Manual of Acupuncture, p. 298; Chinese Acupuncture & Moxibustion, p. 184; cross-referenced against multiple online sources.

Where is BL-39 located?

• A Manual of Acupuncture (p. 298): At the back of the knee, on the popliteal crease and towards its lateral end, in the depression medial to the tendon of biceps femoris.
• Chinese Acupuncture and Moxibustion (p. 184): Lateral to Weizhong (BL-40), on the medial border of the tendon of m. biceps femoris.

How is BL-39 Wei Yang needled, and what is in the popliteal fossa?

Reference record only — this documents what the standard texts and the published anatomical literature state, not instruction for a reader. Sacred Lotus sources & references record perpendicular insertion of 0.5-1.0 inch at BL-39, with moxibustion noted as applicable. Chinese Acupuncture & Moxibustion (p. 184) and Deadman & Al-Khafaji (p. 298) record a comparable perpendicular range.

• Angle documented: perpendicular.
• Depth documented: approximately 0.5-1.0 inch.
• Moxibustion: documented as applicable.

Safety reference: the anatomy of this corner of the fossa

BL-39 lies at the lateral end of the popliteal crease, on the inner side of the biceps femoris tendon. Standard anatomical descriptions place the popliteal artery and vein deep in the centre of the fossa — that is, beneath and medial to BL-39, under BL-40 — and the common peroneal (common fibular) nerve running along the lateral border of the fossa, close to the biceps femoris tendon that forms BL-39's landmark. So the vessels are not directly under this point, while a major peripheral nerve passes alongside it. That is the reason the texts record a fixed, modest depth here rather than a deep insertion.

Being precise about what has been measured. The one imaging study that puts a number on safe depth in this fossa measured BL-40, not BL-39. Investigators located BL-40 on knee MRI scans in 124 participants and reported a mean safe depth of 18.51 ± 3.56 mm, rising with body mass index, together with the finding that the popliteal artery deviated laterally from the point in about nine of every ten people (Hou HK, Liu CZ, Lin LL, Acupunct Med 2021;39(4):343-50, PMID 33032445). Those figures belong to the neighbouring point and are quoted here only as regional context; no equivalent measurement of BL-39 was found, and this record does not transfer the number across. Our BL-40 record sets out the same study, together with the small published series of popliteal artery pseudoaneurysms following acupuncture in that fossa.

Depth beyond what the texts record. The published literature does contain a case report of electroacupuncture following deliberately deep needle insertion at BL-39 and BL-40 in an acute anterior cruciate ligament injury (Deng C et al., Acupunct Med 2023;41(1):58-60, PMID 36305618). It is a single-patient report describing a technique that goes beyond the standard textbook depth, and it is recorded here as a fact about the literature, not as a documented method. Standard clean-needle practice applies. Acupuncture is performed by qualified practitioners; this record documents the literature and is not a technique guide.

Source: Sacred Lotus sources & references (existing needling record); Chinese Acupuncture & Moxibustion, p. 184; Deadman & Al-Khafaji, A Manual of Acupuncture, p. 298; standard descriptive anatomy of the popliteal fossa; PubMed PMID 33032445 (measured at BL-40) and PMID 36305618, each checked as active and not retracted.

What does the name Wei Yang mean?

Wei Yang means "Bend Yang" — wei, to bend, bow or crook, and yang, here in its plain anatomical sense of the outer or lateral side. The name is purely topographical: the outer end of the bend behind the knee. Its neighbour BL-40 Wei Zhong, "Bend Middle", takes the centre of the same crease, and the pair of names between them map the crease. The plainness of both names places them in the oldest layer of the point nomenclature, where names describe location rather than function. Our BL-40 record reads the pair the same way.

Why is a San Jiao point on the Bladder channel?

Because the Lower He-Sea scheme is organised by organ, not by channel. The Ling Shu holds that the six fu organs are reached from below the knee, on the three yang channels of the leg. The Stomach, Gallbladder and Bladder each have a He-Sea point on their own leg channel and so keep it. The Large Intestine, Small Intestine and San Jiao run on the arm, so the classics assign each a borrowed point on a leg channel: ST-37 for the Large Intestine, ST-39 for the Small Intestine, and BL-39 for the San Jiao. BL-39 is therefore a Bladder-channel point in every ordinary sense — it is needled on that channel, it carries Bladder-channel back and leg indications, and it is numbered in that channel's sequence — while its category, and half its indication list, belong to a different organ entirely. Readers who expect a point's function to follow its channel find this point puzzling, and the puzzle is real rather than a slip in the sources.

Has the BL-39 and San Jiao link been questioned?

Yes, and it is worth saying so. A review of the development of Lower He-Sea theory in the Chinese acupuncture literature argues that the scheme was not built all at once: the clinical experience behind ST-36 is deep and well attested, whereas the recorded indications of ST-39 for the Small Intestine, and the link between BL-39 Wei Yang and the San Jiao, are not supported by the same accumulated body of use. The authors treat Lower He-Sea theory as an incomplete construction assembled after the five-shu points, reflecting a shift in how the classics understood the relationship between the yang channels and the internal organs (Zhao JS, Shi XD, Zhongguo Zhen Jiu 2011;31(7):646-52, PMID 21823297). The site records the classification as the tradition transmits it, and records this scholarly qualification alongside it.

Is there research on BL-39 Wei Yang?

There is very little point-specific research on BL-39, and the site will not present the literature as though there were more. Four items were located, none of them a controlled trial isolating the point:

• Theory review. The analysis of Lower He-Sea theory described above, which examines the BL-39 and San Jiao relationship directly (PMID 21823297).
• Case report. Electroacupuncture after deep needle insertion at BL-39 and BL-40 in an acute anterior cruciate ligament injury — a single patient, reported for the technique (PMID 36305618).
• Uncontrolled case series. Thirty-six cases of urinary retention treated with two alternating point groups, the second of which was BL-23, BL-28, BL-32 and BL-39, reporting 30 cures and a 94% total effective rate (Zhang D, J Tradit Chin Med 2008;28(2):83-5, PMID 18652110). There is no control group, no blinding and no randomisation, so this is a report of a protocol's use rather than evidence of the point's effect — but it does record BL-39 being used in its classical urinary territory.
• A caution about the indexed literature. At least one animal study in PubMed applies the code "BL39" to Xuanzhong, which is in fact GB-39, the Hui-Meeting point for marrow, held in this library under that name. Point-code searches on this point therefore have to be read rather than counted, and one apparent BL-39 study is not about BL-39 at all.

No adequately powered randomised trial isolates BL-39 as the tested variable, in urinary retention, oedema or low back pain. Trials that include it among a dozen needles are studies of a protocol.

How does BL-39 differ from the points near it?

BL-40 Wei Zhong is the comparison that matters, and the two are as different as neighbours can be. BL-40 sits at the centre of the same crease and is the Bladder channel's own He-Sea and Earth point, one of the four Gao Wu Command Points, and the classical command point of the lumbar region — a major point for the back, and one carrying a documented vascular hazard because the popliteal vessels lie beneath it. BL-39 sits at the outer end of the crease, is a minor point for the back, and earns its place in the canon for fluids rather than for pain. BL-38 Fu Xi lies just above BL-39 on the same lateral line. Further down, BL-57 Cheng Shan in the belly of the calf and BL-60 Kun Lun at the ankle are the channel's other distal points of weight. Among fluid-regulating points, SP-09 Yin Ling Quan is BL-39's functional counterpart on a yin channel, and GB-39 Xuan Zhong — despite the similar-looking code — is an unrelated point on the outer lower leg and the Hui-Meeting point for marrow.

Source: Sacred Lotus sources & references (name, categories and cross-referenced point records); Ling Shu, on the Lower He-Sea points; Deadman & Al-Khafaji, A Manual of Acupuncture, p. 298; Chinese Acupuncture & Moxibustion, p. 184; PubMed PMID 21823297, 36305618, 18652110, each checked as active and not retracted; cross-referenced against multiple online sources.