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Chest muscles | Human Anatomy


chest muscles

The pectoralis major is fan-shaped muscle that has two anatomic sections, or heads. The upper clavicular head arises from the clavicle (collarbone), and the lower sternal head arises from the sternum (breastbone). The two heads pass putward across the chest wall and merge into a single tendon that attaches to the humerus bone in the upper arm. As the muscle inserts, the tendon twists so that the upper head attaches beneath the lower head. When the pectoralis muscle contracts, movement takes place at the shoulder joint. When the pectoralis muscle contracts, movement takes place at the shoulder joint. Pectoralis major adducts, flexes, and internally rotates the arm, thus moving the arm forward and across the chest during movements such as a push-up or a bear hug. Even though the muscle has only two sections (upper, middle, and lower), depending on the angle through which the arm is moved. As the position of the shoulder joint changes, certain fibers of the chest muscle have better mechanical advantage to create motion. Other fibers of the chest muscle are still active but are not able to contract as much because of the shoulder position.

The side wall of the chest is formed by the serratus anterior. This
muscle arises f rom the scapula behind, and it passes forward around
the chest wall to attac to the upper eight ribs. The serrated edge of
this muscle emerges from beneath the outer margin of the pectoralis
muscle. The serratus anterior pulls (protracts) the scapula forward,
stabilizing it against the rib cage. The serratus anterior is active during
most chest exercises and works especially hard during the lockout
phase of a push-up or bench press. The pectoralis minor muscle lies
deep beneath the pectoralis major and is not visible. It has only a minor
function and does not contribute to the size of the chest.

Source: wikipedia.org | book – Bodybuilding Anatomy by Nick Evans

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Shoulder muscles | Human Anatomy


shoulder muscles

The Shoulder muscles ,also called “ball-and-socket” are joint between the humerus bone of the upper arm and scapula bone (shoulder blade).

Six main movements occur at the shoulder: flexion, extension, abduction, adduction, internal rotation, and external rotation.

  • Flexion – upper arm is elevated forward toward the face
  • Extension – the arms move backward behind the plane of the body
  • Abduction – the arm moves up and out to the side of body
  • Adduction – the arm is pulled in toward the side of body

Horizontal adduction occur when the arm moves in a horizontal plane at shoulder level, such as during chest flys or rear deltoid flys.

Shoulder muscles

The deltoid muscle of the shoulder consists of three separate sections, or heads, each capable of moving the arm in different directions. From a broad tendon attachment above the shoulder joint, the deltoid’s three heads merge into a single tendon that attaches to the humerus bone of the upper arm. The anterior deltoid (in front) attaches to the clavicle and raises the arm forward (shoulder flexion). The lateral deltoid (at the side) attaches to the acromion and lifts the arm outward to the side (abduction). The posterior deltoid (behind) attaches to the scapula and moves the arm backward (shoulder extension).

The rotator cuff is a group of four muscles that form a protective sleeve around the shoulder joint. Despite being a barely visible muscle group, the rotator cuff is essential for shoulder stability and strength. All four muscles originate from the scapula (shoulder blade) and pass across the shoulder joint to attach onto the humerus bone of the upper arm. The supraspinatus lies above the joint and raises (abducts) the arm up and outward-as when hailing a taxi. Infraspinatus and teres minor are located behind and act to rotate the arm out-as when hitchhiking. Subscapularis is situated in front and rotates the arm inward-as when folding your arms across the chest.

Source: wikipedia.org | book – Bodybuilding Anatomy by Nick Evans