Many different muscles help control movements in the upper arm. The thorax serves as a major anchor point for each of these muscles. The most substantial anchor points in the thorax include the scapula, clavicle, sternum, and ribs.
Much of the discussion in this topic refers to anatomical names for movements. If you are not familiar with this terminology then you may wish to review these terms in the article on Anatomical Terminology. You will find the material in the current article easier to follow and understand if you have a sound appreciation for anatomical references. You may also find it beneficial to review related skeletal structures when exploring this topic since much of the discussion relates to where a muscle connects to skeletal structures.
There are numerous diagrams depicting the various muscles under discussion in this article. You can click on most of these diagrams to view a larger version of each image. You will need to allow pop ups for this website to view the larger images. Usually the larger image is of substantially greater size allowing observation of greater detail.
Muscles Affecting Humerus MovementsMovement of the upper arm is dependent largely upon skeletal muscles found in the shoulder and upper torso. The diagram at right identifies the muscles involved in these movements.
These muscles provide extension, flexion, abduction, rotation (both medial and lateral), and adduction of the humerus or upper arm. These muscles anchor to the clavicle, scapula, spine, or ribs and support the dynamic range of movements required of the upper arm.
DeltoidThe deltoid muscle plays a major role in humerus movements. Deltoid muscles provide extension, flexion, and shoulder rotation. Deltoid muscles have a triangular shape and have three separate muscle bands that control various aspects of humerus movement.
The deltoid originates on the clavicle and scapula (in two places), and inserts on the humerus. The three separate attachment points on the clavicle and scapula form the head of three separate muscle bands in the deltoid muscle, each of which is independently controlled. All three bands merge via a single large tendon to attach to the humerus about mid-way down from its superior end on the lateral side of the bone. The deltoid insertion (attachment) point on the humerus is the deltoid tuberosity.
The anterior band (attached to the lateral one-third of the clavicle and shown in red) pulls the humerus in and toward the center of the body. This causes flexing and medial rotation of the humerus. The lateral muscle band (shown in green) pulls the humerus toward the acromion portion of the scapula. This pulls the humerus up and away from the body via abduction. The posterior muscle band (shown in blue) originates along the entire length of the scapula spine. It pulls the humerus back in extension and rotates the humerus laterally. If you roll a bowling ball, pitch a fast ball, rake the lawn, or do a jumping jack you will heavily rely on the deltoid muscles to perform major parts of these actions.
The latissimus dorsi functions as the antagonistic muscle to the deltoid muscle.
SubcapularisThe subcapularis muscle is a large triangular deep body muscle that originates on the anterior surface of the scapula. The body of the muscle fills the subscapular fossa surface of the scapula. The subcapularis muscle functions to cause medial rotation of the humerus as well as adduction, bringing the arm down and forward. It inserts into the lesser tubercle of the humerus at the front of the shoulder joint.
The muscle is also situated to help prevent dislocation of the humerus from the rest of the shoulder joint.
The antagonist (opposing action) muscles to the subcapularis are the infraspinatus and teres minor muscles.
Teres MajorThe teres major muscle originates at the lower portion and posterior side of the scapula. It connects to the upper end of the humerus. It is a narrow but thick muscle that aids in medial rotation and adduction of the humerus.
The serratus anterior is a very large muscle used to help project the entire shoulder area when the arm swings forward. If someone is throwing a hay-maker punch then the serratus anterior helps to pull the scapula forward allowing the arm to extend forward at the shoulder. It also assists with upward rotation of the arm.The muscle connects via multiple tendons to ribs 1 through 9. Because of its many attachment points early anatomists likened it to a saw-tooth shape. It derives its name in part from its serrated shape. Knowing this may make it somewhat easier to remember the name.
The serratus anterior muscle connects to the ventral surface of the medial edge of the scapula (i.e. along to the front interior edge of the scapula). When the muscle contracts it pulls the entire scapula forward and around the rib cage. This allows the arm to extend further forward.
As you raise your arms the serratus anterior muscles tilt your scapula so that your shoulder points more upward. This provides increased range of motion and allows your humerus to rotate while in a raised position.
The pectoralis major muscle is the large muscle in the upper chest. It is a fan-shaped (convergent) muscle that functions to flex, extend, and rotate the humerus. The muscle anchors along the medial half of the clavicle, down the length of the sternum and then down toward the eighth rib. The opposite tip of the muscle inserts at the humerus.
These muscles provide flexion of the humerus. This provides the front lifting motion you would experience when pushing a bowling ball forward. In addition the muscles provide a powerful adduction force that allows you to briskly and forcefully lower your arm. The pectoralis major provide the force necessary to medially rotate the humerus enabling actions such as a powerful Chudan Uke.
The muscle band that originates along the clavicle (shown in blue) supports medial rotation, horizontal adduction and flexion. The band that originates along the sternum and ribs (shown in red) is antagonistic to the clavicle band of the muscle. The sternum band therefore provides support for downward and forward forces. It also contributes to medial rotation of the humerus during adduction.
Pectoralis MinorThe pectoralis minor muscle is in the chest, posterior to the pectoralis major muscle. The pectoralis minor muscle inserts at the front third, fourth, and fifth ribs. The opposite end of the muscle inserts at the medial border of the scapula’s coracoid process. The muscle does not directly attach to nor directly move the humerus, Instead, it moves the scapula which may in turn cause the humerus to shift to a new location or orientation.
When the muscle contracts it may have one of two different effects. If the shoulder remains relaxed and the thorax remains relatively rigid then the muscle will pull the scapula down and forward, thereby causing a tilt and rotation of the shoulder. The contraction pulls the scapula inferiorly and anteriorly, causing the noted effects.
Alternately, if the shoulders are held immobile then the muscle contraction will cause the ribs to pull upward slightly while leaving the scapula relatively immobile. This expands the size of the chest cavity aiding in the inhalation process. If you are taking a large deep breath then the pectoralis minor muscles are probably involved.
The latissimus dorsi are the largest muscles in the upper body. These are large triangular muscles used when you exert a strong pulling force. The main function of the latissimus dorsi is adduction of the upper arm, especially if you are doing something like a pull-up. It also functions to pull the arm back in extension. This is the type of motion you experience when rowing or simply walking. In addition the latissimus dorsi rotate the humerus medially. This enables you to touch the elbow of your opposite arm or perform cross body passes using the Nunchaku.
The muscle originates along the crest of the sacrum iliac and the inferior portions of the spinal column. The attachments to the vertebrae continue up to the eighth or ninth rib. These attachment points can vary significantly between individuals. The muscle fibers merge near the humerus and attach via a tendon on the posterior of the upper humerus.
The supraspinatus muscle sits on the posterior of the upper shoulder. The muscle originates above the spine on the scapula and inserts at the lateral superior portion (the greater tubercle) of the humerus. When the muscle contracts it pulls on the upper outer edge of the humerus to produce abduction of the limb. When your arms are at your side the supraspinatus muscle is the primary muscle that lifts (abducts) the arm for the first ten or fifteen degrees. At that point the deltoid muscles provide most of the force necessary to abduct the humerus further.
CoracobrachialisThe coracobrachialis muscle stretches from
the top of the scapula (at the coracoid process of the scapula) and down to the posterior of the humerus. Contraction of the coracobrachialis pulls the arm forward in flexion and pulls it inward in adduction. It also induces slight medial rotation of the humerus. Like many of the other muscles in this area it also helps to restrict undesirable movement so that the shoulder joint remains intact.
InfraspinatusThe infraspinatus muscle originates along the medial surfaces of the infraspinous fossa of the scapula. It travels under the scapula spine and inserts at the middle impression on the greater tubercle of the humerus.
The infraspinatus muscle is primarily responsible for lateral (outward) rotation of the humerus. Contracting the muscle may also pull the shoulder back. Like most other muscles that connect near the head of the humerus it also functions to maintain integrity of the shoulder joint.
The diagram below shows the many points at which various muscles attached to the humerus. This is a picture of the left humerus showing the various tendon processes.
A- Supraspinatus muscle
B- Latissimus dorsi muscle
C- Pectoralis major muscle
D- Deltoid muscle
F- Extensor carpi radialis longus muscle
G- Common extensor tendon
H- Subscapularis muscle
I- Teres major muscle
J- Coracobrachialis muscle
K- Brachialis muscle
L- Pronator teres muscle
M- Common flexor tendon
We do not cover all of these connection points, particularly those near the elbow, in this article.