BL40 (Weizhong) — Bend Middle
BL40, known as Weizhong or Bend Middle, is located at the back of the knee and is a major point for acute lower back pain, sciatica, and knee discomfort.
At a Glance
| Meridian | Bladder (BL) |
|---|---|
| Body region | Center of the crease behind the knee (popliteal fossa) |
| Best for | Acute lower back pain, sciatica, knee pain and weak legs |
| Difficulty | Easy to reach with both thumbs; a massage stick or tennis ball helps if you are stiff |
| Hold time | 30–60 seconds per leg |
| Frequency | 1–3 times daily |
| Pairs well with | GB34 (Yanglingquan), BL60 (Kunlun), ST36 (Zusanli) |
| Skip if | Varicose veins or a history of blood clots behind the knee, broken skin, or recent knee surgery (see Precautions) |
Why BL40 Matters
BL40 sits in the crease behind the knee, far from the area it treats, yet it is widely regarded as the most important acupressure point for lower back pain. The Bladder meridian runs the length of the back and down the leg, connecting the popliteal crease directly to the lower back.
Its name, Weizhong, meaning Bend Middle, refers to its position in the center of the bend behind the knee. In clinical tradition it is one of the most frequently used points for acute lower back strain, and it appears routinely in back-pain protocols — which is why a point so far from the lower back is worth learning even if you only press it occasionally.
Location
BL40 is at the back of the knee, in the exact center of the popliteal crease — the horizontal skin crease behind the knee joint. To find it, sit with the knee slightly bent so the crease is visible, then place a thumb in the center of that crease, midway between the two hamstring tendons.
Three quick confirmations you have the right spot: (1) it is the midpoint of the crease, not the inner or outer edge of the knee; (2) pressing it with the knee slightly bent produces a deep, dull ache rather than a sharp or superficial sensation; (3) it usually sits in a slight hollow between the hamstring tendons — if you feel only bone or tendon, you are slightly off-center.
When to Use BL40 (and When Not)
Use it when
- • You have sudden or nagging lower back pain, especially from a strain
- • Sciatica — pain radiating from the lower back down the back of the leg
- • Your knees feel stiff or your legs feel weak or heavy
- • Your hamstrings or calves are tight or cramping
Hold off if
- • You can see varicose veins behind the knee, or you have a history of blood clots (DVT)
- • There is broken skin, a rash, or swelling in the popliteal area
- • You recently had knee surgery, a knee injury, or a Baker's cyst behind the knee
- • Back pain comes with numbness, weakness, or loss of bowel or bladder control — get urgent care
Use the Hold off column as a safety filter: BL40 is a comfort practice for back and leg tension — never press hard over veins, and acute red-flag back pain needs urgent medical care.
Benefits & Uses
- Lower back pain: BL40 is considered one of the most effective points for acute lower back strain and discomfort.
- Sciatica: It helps relieve radiating leg pain that follows the sciatic pathway from the lower back.
- Knee pain and weak legs: It eases stiffness and discomfort in the knee and can help legs that feel heavy or unsteady.
- Hamstring and calf tension: It relaxes tight hamstrings and calves and helps with leg cramps.
- Post-lifting recovery: Pressed after a day of standing, lifting, or heavy activity, it helps release the pull that runs from the lower back down the back of the leg.
How to Massage BL40
Press with the knee slightly bent so the crease is soft and relaxed — pressing with the knee locked straight makes the point hard to reach and uncomfortable. Both thumbs on the center of the crease works best; if it is awkward, a massage stick, a tennis ball against a wall, or a partner can help.
- Sit with your knee slightly bent and leg relaxed.
- Place your thumbs on the BL40 point behind your knee.
- Apply firm, steady pressure with a small circular motion.
- Hold for 30–60 seconds, then gently straighten and bend your leg.
- Repeat on the other leg as needed, 1–3 times daily.
Common mistake to avoid: pressing hard over visible veins, or pressing with the knee fully straight. The target sensation is a deep, dull ache in the middle of the crease — if you feel a sharp or electric twinge down the leg, or you are pressing over varicose veins, ease off.
Combine BL40 with These Points
A full back-and-leg routine is more effective than pressing one point. Pick the row closest to your situation and work the points in the order shown, 30–60 seconds each.
| Goal / symptom | Routine (in order) |
|---|---|
| Acute lower back strain | BL40 → GB34, gentle, 2–3 times daily |
| Sciatica / radiating leg pain | BL40 → GB34 → BL60, working down the leg, 30–60s each |
| Knee pain and stiff legs | BL40 → ST36, then gentle knee bends |
| After a day of standing or lifting | BL40 + ST36, 30–60s each, then a short walk |
For a fuller program, see the leg acupressure points body guide, and pair with our GB34 (Yanglingquan) and BL60 (Kunlun) point guides for leg pain that runs down the outside or back of the leg.
What to Expect
First session (today)
BL40 is often tender, and pressing it produces a deep, dull ache. Many people feel the lower back "let go" a little within a few minutes, though acute strain can return as the day goes on. Do not expect a cure after one press.
Days 3–7 (consistent daily practice)
With 1–2 sessions per day, tenderness at the point usually eases and acute lower back strain often settles. This matches the pattern in studies of acupressure for low back pain, where benefits appear after several days of regular use.
Weeks 2–4
For chronic or recurring back pain, pair BL40 with movement, stretching, and — ideally — a physiotherapy plan. Acupressure is a complement, not a replacement. No improvement after 2–3 weeks, or any red-flag symptoms, means seeing a clinician.
Science & Research
Lower back pain is one of the most studied areas in acupressure research. Systematic reviews and randomized controlled trials have examined acupressure as an adjunct for back pain, with results that are generally promising but limited in quality. Meta-analyses of acupressure for pain tend to show a positive direction of effect, though study samples are often small and methods vary.
Like other manual therapies, acupressure is hard to blind, so the specific contribution of a point such as BL40 is difficult to separate from the general effects of touch, pressure, and expectation. The evidence base is encouraging but not definitive — we lay out what is known, and what is still missing, in our does acupressure work? review.
Verifiable sources
- Chen YW, Wang HH. The effectiveness of acupressure on relieving pain: a systematic review. Pain Management Nursing. 2014;15(2):539-550. PMID 23415783 · DOI
The review above evaluated acupressure for pain, including the low-back and leg complaints this point is most used for. It is not a study of BL40 in isolation.
Precautions
- Avoid deep pressure over varicose veins, and never press if you have a history of blood clots (DVT).
- Do not press if there is broken skin, a rash, or swelling behind the knee.
- Avoid the point after recent knee surgery, a Baker's cyst, or an acute knee injury.
- Use gentle pressure on the elderly or anyone with fragile skin.
- Stop if you feel sharp or shooting pain down the leg.
Red Flags — See a Professional
Stop self-treatment and see a doctor immediately if you notice any of the following:
- Sudden severe back pain with numbness, weakness, or pins-and-needles in the legs
- Loss of bowel or bladder control, or numbness in the groin or saddle area — get emergency care
- New swelling, warmth, or redness in the calf (possible blood clot — do not massage the area)
- Pain down the leg that is getting worse
- Back pain that has not improved after 2–3 weeks of regular acupressure