When the leg is free from support, the piriformis muscle exhibits great strength: by contracting it, the thigh can be turned outward. It abducts the thigh bent at 90°.
When all its fibers contract simultaneously, the thigh is abducted. When the leg is free, its anterior fibers rotate the thigh inward. When the anterior fibers contract, the thigh rotates inward (pronates) as with the gluteus medius.
The gluteus medius is the most powerful abductor of the hip. The anterior group of its bundles rotates the hip slightly inward. The muscle is mainly responsible for stabilizing the pelvis when transferring body weight to one leg.
Extends the thigh at the hip joint, rotating it slightly outward. By contracting the upper part of the gluteus maximus, the thigh is abducted. By contracting, the lower part of the gluteus maximus helps to abduct the bent thigh against a large load.
The iliopsoas muscle flexes the hip. It also helps slightly with external rotation of the hip, and sometimes helps with hip abduction. It helps with lumbar flexion if the body is bent forward.
Trigger zones of this muscle often cause pain in the shoulder blade and shoulder area. A dull, deep pain under the upper edge of the shoulder blade is characteristic of damage to the posterior superior serratus muscle.
Involvement of the deepest paravertebral rotator muscles causes pain along the midline of the back and referred pain upon percussion of adjacent spinous processes.
Rotation of the spine is carried out by the semispinalis muscles, multifidus muscles, rotator muscles, oblique abdominal muscles with unilateral contraction, some action is exerted by the rhomboid muscles and the posterior superior serratus muscle.
With unilateral contraction, it participates in the tilt of the spine with the rib cage. With tonic contraction on both sides, it holds the spine in a vertical position.
