Pohu

What is BL42?

BL42 (Pohu) is a point on the outer Bladder channel of the upper back, level with the third thoracic vertebra, beside the shoulder blade.

Its Chinese name, Pohu, is usually translated as "Door of the Corporeal Soul". In classical theory the Po is the part of the spirit housed by the Lung, so BL42 sits in the outer line of Bladder channel points that mirror the Lung's back transport point. Texts group it with breathing complaints, long-standing cough, and the tiredness and low spirits that were thought to follow lung weakness.

It is a standard point in acupuncture curricula, but it is a second-line one. The inner-line point at the same level is used far more often, and BL42 is usually added to it rather than used alone.

Here is the honest verdict on the evidence: there are no controlled human trials testing finger pressure on BL42 for any condition. What exists is indirect — small, mostly unblinded studies of multi-point acupressure for breathlessness or upper-back muscle pain, which cannot tell you what this one point does. Treat any confident claim about BL42 with suspicion.

Two things worth stating once, clearly. First, the fact that a point has been taught for two thousand years tells you that people found it useful enough to keep teaching; it does not tell you that it outperforms a placebo. Second, long tradition is not a safety record either. Nobody ran safety studies on pressing the upper back, so the sensible cautions come from anatomy and common sense, not from the classics.

Everything on this page is self-applied finger pressure, or pressure applied by a willing partner. Nothing here involves needles, heat or anything that breaks the skin. Used gently on healthy skin over muscle, that is a low-risk thing to do — but it is not a substitute for treatment of a lung condition.

Where is BL42 and how do you find it?

BL42 sits about four thumb-widths out from the spine, level with the bottom of the third thoracic spine bump, near the inner edge of the shoulder blade.

• Find the big neck bump first. Bend your head forward and run a finger down the back of your neck. The largest bump you meet is the seventh neck vertebra (C7).
• Count down three bumps. From C7, walk your finger down over the next three bony knobs. The third one is the spine of the third thoracic vertebra (T3). Work from the lower edge of that knob.
• Cross-check with the shoulder blade. The inner end of the ridge along the top of your shoulder blade sits at roughly the same level. If your two landmarks agree, you are in the right band.
• Measure outwards. From the midline of the spine, move sideways about 3 cun — four of your own thumb-widths, or roughly 6 to 7 cm on an average adult. That lands you close to the inner border of the shoulder blade.
• Feel for muscle, not bone. The point lies in the thick band of muscle between the spine and the shoulder blade edge. It often feels ropy or tender, and firm pressure may refer a dull ache across the upper back.

Distances scale to the body, so use your own thumb, not a ruler. On a small frame the point sits closer in; on a broad back, further out.

Do not confuse BL42 with the inner-line point at the same height, which is half that distance from the spine — two thumb-widths rather than four. Both are real points. BL42 is the outer one, essentially at the shoulder blade's inner edge.

Most people cannot reach their own upper back comfortably. A tennis ball against a wall, or a partner's thumb, is the practical answer.

How do you apply pressure to BL42?

1. Get access to the area. Sit upright or stand with your back to a wall. If a partner is helping, sit forward on a chair with your arms resting on a table so the shoulder blades slide apart.
2. Locate and confirm. Find the spot using the landmarks above, then press lightly and feel around. You want soft muscle with a tender, slightly ropy quality — not the hard ridge of a bone.
3. Press with a flat thumb or finger pads. Lean in slowly and straight towards the body. A ball against a wall works well: place it on the point and let your body weight do the work as you lean back.
4. Use a firm but comfortable pressure. Aim for a 4 to 6 out of 10 — a satisfying ache, never a sharp or burning pain. If you are wincing or holding your breath, it is too hard.
5. Hold and breathe. Keep steady pressure for 30 to 60 seconds, breathing out slowly as you press. Small, slow circles are fine if static pressure feels dull.
6. Do both sides. The point is paired. Treat the left and right the same way, even if only one side feels tender.
7. Keep sessions short. Two or three rounds per side, once or twice a day, is plenty. Five minutes total is a reasonable ceiling.

Stop straight away if you feel sharp pain, pins and needles running into an arm, dizziness, or any increase in breathlessness. Those are signals to come off the point, not to push through.

Let the area recover for a day if it is sore afterwards. Deep pressure on upper-back muscle can leave a bruise-like tenderness for 24 hours, especially if you used a ball. That is a sign to go lighter next time, not a sign it worked.

Never use BL42 as a response to sudden breathlessness, chest pain or an asthma attack. Use your prescribed medication and get medical help.

What is BL42 traditionally used for?

• Cough and breathing complaints. Classical sources link BL42 to chronic cough, wheezing and what older texts called consumption. No human trial has tested the point for any of these. Small acupressure studies in lung disease use several points at once, so they cannot separate out BL42.
• Chest tightness. Tradition describes the point as opening the chest and settling the breath. Any real effect here is unmeasured; a slow, breath-paced press may simply be relaxing, which is a sensible thing to call it.
• Upper back and shoulder blade tension. The point lies in muscle that commonly tightens from desk work and carrying. Massage and pressure to tight upper-back muscle gives short-term relief in small studies — that is a fair, modest claim for the area, not proof of a channel effect.
• Grief and low spirits. The Po is the Lung's spirit in classical theory, so Pohu was used for sadness, worry and restlessness after loss. This is tradition and metaphor. There is no human evidence that pressing BL42 changes mood, and low mood that lingers needs proper support.
• Night sweats and fatigue. Older texts list BL42 for sweating at night and general depletion. Nothing in the modern literature tests this. Night sweats with weight loss or fever need a doctor, not a pressure point.

The useful summary: BL42 has a long, consistent traditional role centred on the lungs and the spirit they were said to house, and almost no point-specific research behind any of it.

If you use it, the defensible reason is that firm pressure on a tight upper back often feels better for a while, and that a few slow breaths while you press are calming. Treat any benefit beyond that as unproven. It should sit alongside your inhalers, physiotherapy or counselling, never in place of them.

Are there tips for using BL42 effectively?

• Use a ball against a wall. Almost nobody can reach their own upper back well. A tennis or lacrosse ball between your back and a wall gives steady, controllable pressure you can adjust by shifting your feet.
• Open the shoulder blade first. Reach your arm across your chest, or round your upper back slightly. This slides the shoulder blade outwards and exposes the muscle where BL42 sits.
• Press on the out-breath. Breathe in, then apply pressure as you breathe out slowly. Muscle gives more easily on the exhale and the rhythm itself is settling.
• Warm the area beforehand. A warm shower or a few shoulder rolls makes the upper back less guarded, so you need less force for the same effect.
• Go lighter than you think. This area bruises easily under a hard ball. Moderate pressure held calmly does more than brief, brutal digging.
• Treat both sides. Working only the sore side can leave you feeling lopsided. Give the quieter side the same attention.
• Pair it with posture, not instead of it. If the tightness comes from a laptop at the wrong height, the pressure point buys you an hour. Fixing the desk buys you the week.
• Keep a simple note. Jot down the date, how long you pressed and what changed. After two weeks you will have a clear answer about whether it does anything for you.
• Give it a fair but limited trial. If two weeks of regular, sensible use changes nothing, that is useful information. Stop and try something else rather than escalating the force.

Comfort matters more than precision here. A broad, warm thumb an inch off the textbook spot beats a sharp nail exactly on it.

What do people get wrong with BL42?

• Expecting a cure. The commonest error. Finger pressure on BL42 will not resolve asthma, COPD, a chest infection or grief. Expecting that leads people to delay care that actually helps.
• Pressing on bone. Landing on the knobbly spine itself or on the hard edge of the shoulder blade, instead of the muscle between them. It hurts, does nothing, and can leave the bone tender for days.
• Confusing it with the inner point. BL42 is four thumb-widths from the midline; the inner-line point at the same level is two. People press the inner one and record it as BL42, which muddles their own results.
• Counting the vertebrae wrong. Starting the count at the wrong bump puts you a level or two off. Cross-check against the inner end of the shoulder blade ridge before you commit.
• Grinding away with a hard ball. Several minutes of heavy rolling on a lacrosse ball produces bruising and a sore back, not a better result. Short, steady holds are the goal.
• Using it during an attack. Reaching for a pressure point while breathless instead of a rescue inhaler is dangerous. Medication first, always.
• Ignoring warning pain. Treating back pain that wakes you at night, follows a fall, or comes with fever as ordinary muscle tightness. That pattern needs assessment, not pressure.
• Having someone press hard on a thin or fragile back. Enthusiastic partners often use far too much force on older or osteoporotic relatives. Pressure should always be the receiver's call.

One quieter mistake: using BL42 as proof that a theory is working. Feeling a dull ache spread across your shoulder is just muscle responding to pressure. It is a pleasant sensation, not a measurement.

What does the research on BL42 actually say?

There is no published controlled human trial of acupressure on BL42 for any condition. That is the plain answer, and it is the same answer for most individual points outside a handful of well-studied ones.

The nearest relevant literature falls into two groups, and neither tells you much about this point specifically.

The first is acupressure and acupuncture for breathlessness in chronic lung disease. Small randomised studies in this field do exist, and some report modest short-term improvements in breathlessness scores or walking distance. They share serious limits: few participants, short follow-up, and almost no credible blinding, since people usually know whether they are being pressed. Crucially, they use multi-point protocols covering the chest, arm and back. Even where a back point near BL42 is included, the design cannot separate one point's contribution from the rest.

The second is manual pressure and massage for upper-back and shoulder muscle pain. Here the evidence is somewhat better and reasonably consistent for short-term relief of tenderness and stiffness. But those studies test massage of a region, not stimulation of a named channel point. They support the general idea that pressing a tight upper back feels better for a while. They say nothing about Pohu as a point.

What this means in practice. If you press BL42 and your shoulders feel looser, that is a real and reasonable thing to experience, most plausibly explained by pressure on muscle and by the calming effect of slow breathing. If someone tells you research shows BL42 treats asthma, grief or night sweats, they are overstating what exists. No study of that kind has been published.

The honest grade is insufficient on the evidence axis. That is not a verdict that the point does nothing. It is a statement that nobody has looked carefully enough to say either way, and you should set your expectations accordingly.