Actions
The pectoralis major has four actions which are primarily responsible for movement of the shoulder joint. The first action is flexion of the humerus, as in throwing a ball side-arm, and in lifting a child. Secondly, it adducts the humerus, as when flapping the arms. Thirdly, it rotates the humerus medially, as occurs when arm-wrestling. The pectoralis major is also responsible for keeping the arm attached to the trunk of the body. It has two different parts which are responsible for different actions. The clavicular part is close to the deltoid muscle and contributes to flexion, horizontal adduction, and inward rotation of the humerus. When at an approximately 110 degree angle, it contributes to abduction of the humerus. The sternocostal part is antagonistic to the clavicular part contributing to downward and forward movement of the arm and inward rotation when accompanied by adduction. The sternal fibers can also contribute to extension, but not beyond anatomical position.
Read more about this topic: Pectoralis Major Muscle
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“However, our fates at least are social. Our courses do not diverge; but as the web of destiny is woven it is fulled, and we are cast more and more into the centre. Men naturally, though feebly, seek this alliance, and their actions faintly foretell it.”
—Henry David Thoreau (1817–1862)