Action
The piriformis muscle is part of the lateral rotators of the hip, along with the quadratus femoris, gemellus inferior, gemellus superior, obturator externus, and obturator internus. The piriformis laterally rotates femur with hip extension and abducts femur with hip flexion. Abduction of the flexed thigh is important in the action of walking because it shifts the body weight to the opposite side of the foot being lifted, which keeps us from falling. The action of the lateral rotators can be understood by crossing your legs to rest an ankle on the knee of the other leg. This causes the femur to rotate and point the knee laterally. The lateral rotators also oppose medial rotation by the gluteus medius and gluteus minimus. At a range of more than 90 degrees the actions of the piriformis are reversed to adduct and internally rotate (medial).
Read more about this topic: Piriformis Muscle
Famous quotes containing the word action:
“Though with their high wrongs I am struck to the quick,
Yet with my nobler reason ‘gainst my fury
Do I take part. The rarer action is
In virtue than in vengeance.”
—William Shakespeare (1564–1616)
“It was the feeling of a passenger on an ocean steamer whose mind will not give him rest until he has been in the engine-room and talked with the engineer. She wanted to see with her own eyes the action of primary forces; to touch with her own eyes the action of primary forces; to touch with her own hand the massive machinery of society; to measure with her own mind the capacity of the motive power. She was bent upon getting to the heart of the great American mystery of democracy and government.”
—Henry Brooks Adams (1838–1918)
“I feel like a white granular mass of amorphous crystals—my formula appears to be isomeric with Spasmotoxin. My aurochloride precipitates into beautiful prismatic needles. My Platinochloride develops octohedron crystals,—with a fine blue florescence. My physiological action is not indifferent. One millionth of a grain injected under the skin of a frog produced instantaneous death accompanied by an orange blossom odor.”
—Lafcadio Hearn (1850–1904)