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Muscles and Nerves of the Pelvis

Sitting presses muscles and nerves against the pelvis, twists the hip rotator muscles, weakens the muscles and circulation, stresses the spine, and stretches some muscles while letting other muscles shorten.

In real life, muscles and nerves get bent around the joints and bones every time you change positions. And the pelvis contains heavy ligaments (not shown) that can trap muscles and nerves.

  Pelvic Muscles (rear view)  
  anatomy pelvis sciatic nerve piriformis muscle
  1.  Sciatic nerve

Gluteal Muscles

  2.  Gluteus minimus
  --  Gluteus maximus (see below)
  --  Gluteus medius (see below)

Lateral Rotator Group

  3.  Piriformis
  4.  Superior gemellus
  5.  Obturator internus
  6.  Inferior gemellus
  7.  Quadratus femoris
  8.  Obturator externus

Anterior Hip Adductors

  9.  Adductor magnus
  10.  Adductor brevis
  11.  Adductor longus


  12.  Biceps femoris
  13.  Semitendinosis
  --  Semimembranosus (not shown)

Painful Muscles

Although the piriformis muscle gets most of the blame for buttock pain not involving the spine, pain is also commonly felt in the other muscles of the lateral rotator group.

When you sit, the quadratus femoris muscle is stretched and twisted and has body weight put on it, so it may ache. The quadratus femoris is about where your weight rests when you sit on a toilet, if your hips are of average width.

The obturator internus may also be involved, because it makes a sharp bend across the edge of the pelvis on its way to the femur, but it's hard to identify this pain. If you are having piriformis syndrome pain in the buttocks, you may also feel a slight twinge near the front of the hip, between the groin and hip. This could be the obturator externus, which shares a nerve with the obturator internus.

Gluteal Muscles Stabilize The Hip

The gluteus maximus is the large muscle that makes up most of the buttocks. It runs from the pelvis to the femur and the iliotibial band.

gluteus maximus gluteus medius muscle
  Before the 20th century, most people had large powerful gluteal muscles from walking long distances every day, lifting and carrying heavy loads, and climbing lots and lots of stairs.

The glutes are also essential for connecting the pelvis to the lower limbs, and keeping the pelvis and back in alignment.

They also protect the smaller muscles of the pelvis from pressure or overwork.

If the glutes are weakened by lack of exercise or sickness, extra stress is put on the piriformis muscle to stabilize the hip.


If the muscle tone of your glutes decreases because you are working a lot of overtime, then you are probably also sitting too many hours a day!

This is a double whammy for the piriformis and other sensitive tissues in the hip, because they are overworked stabilizing the hip and you are sitting on them all day

Bad Chairs Make Problems Worse

If you have even minor physical problems, they can be multiplied by a bad chair. If your knees are slightly higher than the seat, the weight on your pelvis and the lateral rotator muscles increases greatly. It creates lower back strain, which can trigger sciatica pain. It also puts stress on the iliosacral joints. If you are experiencing pain, do not sit on a soft sofa or bed!

ergonomic sciatica piriformis syndrome

The buttocks cover the sciatic nerve and the ischium ("sit bones") when you stand. But when you sit, the gluteus maximus slides up a couple inches, exposing the sciatic nerve, the ischium, and small muscles to pressure from the chair.

You can prove this to yourself, by sitting on the edge of a table, and you can bounce up and down by clenching your gluteus maximus. Then slide back on the table until your thighs are fully supported by the table, and you will find that more of your weight is on the pelvis and smaller muscles. If you can't feel this, you may need a training program to restore muscle mass and muscle tone.

If the glutes are strong, they still provide some protection to this area when you sit. If your muscle tone drops suddenly because of something like a mild case of the flu, you might also have piriformis pain because your glutes have lost muscle tone.

Sciatica And Other Causes Of Pain

There are many other causes of pain in this region, including sciatica caused by bulging or herniated lumbar disks and spinal stenosis. A cushion that elevates the hips above the knees can be helpful, but only with a physician's approval.

Other causes of pain can include infections, arthritis, tumors, and various assymetries of the legs and torso. See your doctor for any pain, numbness, or change in health, and have regular checkups.


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