Chengfu (BL36): The Buttock Crease Point for Sciatic Ache Down the Back of the Leg

Where Chengfu Sits

This point sits in the middle of the crease where the buttock meets the back of the thigh, right in line with the bony point you sit on. It is a quiet, unglamorous spot, and most of us would rather not fuss over it. That is part of why it gets overlooked, even by people whose ache runs straight through it.

It belongs to the longest line on the traditional map, the one Vietnamese and Chinese texts call the Bladder channel. That line begins at the inner corner of the eye, runs over the top of the head and down both sides of the spine, then crosses the buttock and travels down the back of the leg to the little toe. At the buttock it leaves the back and turns onto the leg, and this is the first stop it makes on the thigh. If your ache runs from the low back into the buttock and down the back of the leg, it follows this line almost exactly.

The old texts place it in the middle of the buttock crease. The modern standard from the World Health Organization says the same, and it needs no measuring. The landmark is the fold itself. Stand up and run your hand down over the curve of the buttock until you feel the crease where the soft tissue of the buttock folds onto the firmer thigh. Follow that crease from the inner thigh to the outer thigh, and stop halfway. On most people that midpoint sits directly under the sitting bone, the hard knob that takes your weight on a firm chair.

Under the skin, three muscles meet here. The large muscle of the buttock (the gluteus maximus) ends at its lower border right above the crease. Below it, two of the hamstring muscles begin from the sitting bone and run down the back of the thigh, the outer one (the biceps femoris) and the inner one (the semitendinosus). The point lies in the soft gap between them. Deeper still runs the largest nerve in the body, the sciatic nerve, on its way from the low back down to the foot. A thinner nerve that serves the skin of the back of the thigh runs closer to the surface. The skin itself is served by the second sacral root. That is why heavy pressure in the wrong place here can send a tingle down the leg.

Why This Spot

On the anatomical side, this crease is a crossroads. Every time you stand up from a chair, climb a step or bend forward, the hamstrings pull on the sitting bone right here. The sciatic nerve passes underneath, and when it is irritated higher up, the tissue around it often turns tender along its path. Many people with a sciatic ache can put a finger on this crease and say, "there, that is where it bites." The area also takes your weight every time you sit, which is why long hours in a car or a hard chair can leave it sore.

In this tradition, the line this point sits on is described as carrying the flow of the whole back of the body, from the head to the heel. A blockage anywhere along it is said to show as pain along the same line. This point sits at the hinge where the line leaves the trunk and enters the leg, so it is used when pain seems stuck at that hinge, refusing to go up or down.

The name says what this crease does. Chengfu means to hold and support: the fold that holds up the buttock and bears the body when you sit. The Vietnamese name, Thừa Phù, carries the same meaning.

What the Old Texts Say About Chengfu

The Systematic Classic of Acupuncture and Moxibustion, the Jiayi Jing, compiled by Huangfu Mi in the third century, places this point in the middle of the crease below the buttock. That description has hardly changed in seventeen hundred years. It is one of the reasons the point is easy to agree on: the crease is the crease, on any body. Older Chinese texts also gave it other names that point to the same place, the flesh where you sit.

The Vietnamese handbook of points and channels by Ngô Trung Triều, published by Hồng Đức, lists it for sciatic pain and for weakness of the lower limbs. It gives a careful way to find it: in the hollow formed by the lower border of the large buttock muscle, the inner border of the outer hamstring and the outer border of the inner hamstring, in the middle of the buttock crease, directly over the point of the sitting bone. That is the same three-muscle junction described above, and it is the method used on this page.

In the wider tradition, this point is rarely used alone. Teachers work down the back of the leg in order: the crease under the buttock, the middle of the thigh, the back of the knee, the calf. The idea is to follow the ache along its own road, one stop at a time, rather than chase it with one forceful press. That habit came from long use, not from proof. It still makes good sense for anyone whose pain travels.

Points That Work With Chengfu

The first partner sits higher, in the side of the buttock. Find the bony knob at the upper outer side of the thigh, then move about a hand's width in toward the base of the spine. That point lies deep in the muscle and is pressed with a tennis ball against a wall. In this tradition the two are paired when pain starts in the buttock and runs down the back and side of the leg.

The second lies on the same line, further down the middle of the back of the thigh, about halfway between this crease and the back of the knee. It is used with this one when the ache runs the whole length of the thigh. The two are easy to work one after the other on the same chair.

The third sits in the middle of the crease at the back of the knee. It is one of the most used points for back and leg pain in this tradition, and it closes the sequence when the ache runs past the knee.

How to Find and Press Chengfu

Getting Into Position

Sit on a firm, flat chair, such as a kitchen or dining chair. A soft sofa lets the ball sink and you lose control. Sit near the front edge with both feet flat on the floor, knees about hip-width apart. Keep a hand on the table or the chair seat so you can lift your weight off at any moment. If sitting is painful, you can lie on your back on a carpeted floor with the knees bent and place the ball under the crease instead.

How to Find It

Lean onto one hip and run your fingers under the other buttock until you feel the crease. Find the hard sitting bone and come down off it onto the thigh. That is the area. Place a tennis ball there, under the crease and in line with the sitting bone, and lower your weight slowly. A softer, well-used ball is kinder than a new one. If you prefer to stand, a long-handled pressing tool with a rounded tip will reach the crease from behind without twisting.

Shift your weight in small steps, forward, back, a little in and a little out. Most of the crease will feel like plain pressure. One spot will sting: a small, sharp, pinpoint tenderness under the ball. That spot is the point. If instead you feel tingling, numbness or an electric line running down the leg, you are on the nerve. Lift your weight off, move the ball slightly toward the outer thigh, and lower more gently.

How to Press It

Once you are on the stinging spot, stay there. Rock your hips in small circles, about the size of a coin, roughly one each second, so the ball rubs the same spot without rolling away from it. Keep your feet on the floor and your hands ready to take weight. If you use a tool, hold it with both hands, place the rounded tip on the spot, and make the same small circles without sliding.

How Much Pressure

A sharp sting under the ball is right. The test comes when you lift off: the sting should fade within moments. If the pain stays after you lift your weight, if it spreads down the leg, or if the area turns swollen, hot or red, stop and leave it alone for several days. Stop at once for any tingling or numbness. If you are holding your breath or gripping the chair, you are pressing too hard. Take some weight onto your hands and feet until you can breathe slowly through the sting.

How Long

One to three minutes on each side. In the first sessions keep to about one minute, because this crease is often far more tender than people expect. Add a little time as the days go on, up to three minutes. Work both sides, even if only one leg aches. Once or twice a day is enough. Longer sessions add soreness, not benefit.

When to Do It

Morning suits a back and leg that are stiff after the night. Late afternoon suits an ache that builds after sitting, driving or gardening. Before bed works well as part of winding down. Do not press in the middle of the night. If sciatic pain wakes you, pressing then tends to keep you awake. Save it for the day and the evening, and tell your doctor if the pain wakes you most nights.

What This Won't Do

It will not move whatever is irritating the nerve. Sciatic pain usually starts higher up, in the lower back, where a worn disc, narrowed space or thickened joint can press on a nerve root. Sometimes it comes from tight muscle deep in the buttock. A tennis ball under the crease cannot reach any of those causes. What it can do is ease tight, tender tissue along the path of the ache and give you something useful to do with your hands. It works best alongside walking, gentle stretching, a good chair and the advice of whoever is looking after your back.

Some sciatic pain is an emergency, and the difference matters more than anything else on this page. Go to a hospital the same day if you have numbness in the saddle area, between the legs or around the back passage, or any new loss of control of your bladder or bowels, or difficulty passing water. Get seen urgently, too, if one leg or foot turns weak, if the foot catches or drags when you walk, or if numbness is spreading. Those signs mean a nerve is being squeezed hard. Pressing a point and waiting is the wrong response. See a doctor promptly for back and leg pain after a fall, pain with fever or unexplained weight loss, or pain that is worse every week.

Safety First

Do not press over skin that is broken, infected, badly bruised or rashy. Leave the area alone with a recent hip or pelvic fracture, a hip replacement in its first months, unexplained swelling or a lump in the buttock or thigh. If you take blood thinners, bruise easily or have reduced feeling in your legs, use a softer ball, lighter weight and shorter sessions, and ask your doctor first. A swollen, warm, painful thigh or calf needs urgent assessment, not pressure.

Stop at once if pain stays after you lift off, spreads, or brings tingling or numbness. Nothing here needs you to push through pain. For the full list of cautions and the situations where pressing on yourself is not appropriate, read the full safety guide before you begin.

Questions People Ask

Where is the Chengfu (BL36) pressure point? Chengfu (BL36) sits on the back of the thigh, in the middle of the crease right below the buttock. It lines up with the bony point you sit on. In English the name is Hold and Support; in Vietnamese it is Thừa Phù. Most people find it easiest by sitting on a tennis ball rather than reaching back with the hand.

How do I press Chengfu if I cannot reach behind me? Use your body weight. Sit on a firm chair with a tennis ball under the crease of one buttock and shift slowly until one spot stings. Rock in small circles over it. If you prefer, a long-handled pressing tool with a rounded tip lets you reach the spot while standing. Both ways keep your shoulders and wrists out of the strain.

Is Chengfu (BL36) good for sciatica? In this tradition it is commonly used for sciatic ache that runs from the buttock down the back of the thigh. It can bring relief to tight, tender tissue around the nerve. It does not change what is pressing on the nerve. If the pain runs below the knee with numbness or weakness, see a doctor before you start.

My leg tingled when I sat on the ball. What should I do? Stop and take your weight off the ball. The large nerve of the leg runs deep under this crease, and tingling or an electric feeling means you are pressing on it. Move the ball a little toward the outer side of the thigh and use less weight. The feeling you want is a small sting under the ball, nothing that travels.

How long should I press Chengfu? One to three minutes on each side. Keep the first sessions to about a minute, because this area is often more tender than people expect. Add a little time as the days go on. Once or twice a day is plenty. Work both sides, even if only one leg aches.

Can I do this in bed at night if the pain wakes me? Better not. Pressing in the middle of the night tends to wake you further. Use the point in the daytime and again in the evening before bed. If sciatic pain wakes you most nights, mention it to your doctor, because night pain is worth checking.

Other Points in This Library

Each of these sits within reach of the same hand. They are often worked in the same sitting.

This page shares general information about a traditional practice. It is not medical advice and does not replace what your doctor has given you. If you are pregnant, managing a health condition, or unsure whether this applies to you, check with your doctor first.

The whole inner edge of the foot, laid out on one page with photographs, is in The Foot Map — the free book. For every point in this library, see the full pressure point index.

(Point shown: BL36 · Chengfu · Hold and Support · Thừa Phù.)