Muscles and Actions
Peroneals evert the foot and assist in plantar flexion of the foot.
The ankle retinaculum dorsiflexes and plantarflexes the foot.
The gastrocnemius plantar flexes the foot.
The soleus muscle plantar flexes the foot when the knee is flexed.
The adductor muscles adduct the leg.
The quadriceps extend the knee. Only the rectus femoris flexes the hip.
The hamstring muscle extends the hip and flexes the knee.
The tensor fasciae latae flexes, abducts, and medial rotates the leg.
The quadratus lumborum side bends and rotates the spine.
The psoas major and iliacus muscles lumbar extend the lumbar when standing, flex the lumbar when bending forward, and primarily flex the hip.
The latissimus dorsi extends the arm, adducts and internally rotates the arm, depresses the arm.
The pectoralis major adducts (and moves the arm across the chest), internally rotates the humerus.
The supraspinatus abducts the arm and pulls the head of the humerus towards the glenoid fossa.
The infraspinatus externally rotates the arm and depresses the humerus when raising the arm.
The teres major internally rotates and aids in resisted adduction of the arm.
The teres minor externally rotates the arm and depresses the humerus.
The subscapularis internally rotates the arm and stabilizes the humerus in the glenoid fossa against the deltoid’s action.
The anterior scalenes bilaterally flex the neck, unilaterally side-bend the neck. If the neck is fixed, aid in respiration by raising the first rib.
The medial scalenes bilaterally flex the neck, unilaterally side-bend the neck. If the neck is fixed, aid in respiration by raising the first rib.
The posterior scalenes stabilize the neck in the neutral position.
The temporalis closes the jaw.
The masseter closes the jaw.
The lower portion of the lateral pterygoid closes the jaw. The upper portion of the lateral pterygoid aids in opening the jaw.
The medial pterygoid closes the jaw.
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With the hyoid bone fixed, the digastric assists in depressing the mandible to open the mouth. With the mandible fixed, the digastric elevates the hyoid bone. The digastric retrudes the lower jaw.
The sternocleidomastoid muscles flex the neck and pull the head forward; bring the chin onto the chest; assist in inspiration of the breath. For thoracic breathers, these muscles may be overdeveloped. Unilaterally the sternocleidomastoid muscle rotates the face toward the opposite side and tilts it upward; with the upper trapezius side-bends the cervical column, drawing the ear to the shoulder.
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