Dominic Stone
The torso, also known as the trunk, is the central area of the body that connects the upper and lower extremities. The torso contains over 30 pairs of skeletal muscles, which are divided into two large groups based on their location. The anterior muscles of the torso are those on the front of the body, including the muscles of the chest, abdomen, and pelvis. The posterior muscles of the torso are associated with movement of the shoulder and back. The torso muscles contribute to essential body activities such as breathing, movement, defecation, and micturition. The rectus abdominis, a long, strap-like, paired muscle that passes vertically over the entire length of the abdomen, acts as a flexor of the trunk. Other muscles that contribute to torso flexion include the internal and external oblique muscles, the latissimus dorsi, and the trapezius.
| Characteristics | Values |
|---|---|
| Number of bones in the torso | 40 |
| Number of pairs of skeletal muscles in the torso | 30 |
| Location of the torso | Central region of the body |
| Functions of the torso muscles | Enable movement of the lumbar and thoracic spine, ribs and proximal limbs, facilitate breathing, and protect vital organs |
| Types of torso muscles | Abdominals, pectorals, erector spinae, serratus anterior and posterior, intercostals, latissimus dorsi, and rhomboids |
| Anterior torso muscles | Pectoralis major and minor |
| Posterior torso muscles | Latissimus dorsi, trapezius |
| Torso muscles involved in flexion | Rectus abdominis, obliques, erector spinae |
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What You'll Learn
Pectoralis major and minor
The pectoralis major and minor muscles are essential for the movement and stability of the anterior thoracic wall and shoulder girdle. The pectoralis major is a large, fan-shaped, superficial muscle located on the anterior thoracic wall. It forms the bulk of the chest area and can be easily seen on the surface in some people, for example, weightlifters. The pectoralis major has three heads, giving it three points of origin: the clavicle, sternum, and ribs. All the fibres converge and insert onto the crest of the greater tubercle of the humerus, a bone in the upper arm. The pectoralis major is involved in a variety of arm movements, such as adduction, internal rotation, flexion, and extension. It is innervated by the medial and lateral pectoral nerves, which are branches of the brachial plexus.
The pectoralis minor is a muscle of the upper chest, located deep to the pectoralis major. It extends from the third to fifth ribs to the coracoid process of the scapula, a bone in the shoulder. This arrangement allows the pectoralis minor to influence scapular depression and protraction, which are crucial for respiration and shoulder function. The pectoralis minor stabilises the scapula by drawing it anteroinferiorly against the thoracic wall, modulating scapulothoracic movements and impacting thoracic posture. The pectoralis minor is supplied by the medial pectoral nerve, carrying fibres from the eighth cervical and first thoracic nerves (C8-T1), which are essential for its activation.
The pectoralis major and minor muscles work together to enable dynamic movement and stabilisation of the shoulder girdle. They coordinate with other muscles such as the deltoid, rotator cuff, and scapular stabilisers to facilitate efficient upper limb movement. The pectoralis major, in particular, contributes significantly to force generation in movements like pushing and bench-pressing due to its large moment arm.
The torso, also called the trunk, is the central area of the body that connects the upper and lower extremities. It contains over 40 bones and 30 pairs of skeletal muscles, including the pectoralis major and minor. The primary functions of the torso muscles are to enable movement of the lumbar and thoracic spine, ribs, and proximal limbs, facilitate breathing, and protect the vital organs.
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Intercostal muscles
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are composed of three layers of muscles: the external, internal, and innermost intercostals. These muscles work together to support the rib cage and assist in breathing by expanding and shrinking the chest cavity.
The external intercostal muscles, also known as intercostalis externus, aid in quiet and forced inhalation. They originate on ribs 1–11 and insert on ribs 2–12. The function of these muscles is to elevate the ribs and bend them open, expanding the thoracic cavity. The internal intercostal muscles, or intercostalis internus, assist in forced expiration. They originate on ribs 2–12 and insert on ribs 1–11, with their fibres passing anteriorly and superiorly. These muscles are responsible for depressing the ribs and bending them inward, thereby decreasing the thoracic cavity.
The innermost intercostal muscles, also referred to as intercostalis intimus, are the deepest layer of the internal intercostal muscles. They originate from the costal groove of one rib and insert onto the superior border of the rib below. These muscles assist the internal and external intercostals in their functions. All three layers of intercostal muscles are innervated by the intercostal nerves and supplied by the intercostal arteries.
Intercostal muscle strains can occur due to various activities such as repetitive torso twisting, overhead movements, weight lifting, high-thrust sports, and contact sports. Symptoms of a strain include pain in the upper back or rib cage, muscle tension and stiffness, and difficulty breathing due to pain.
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Rectus abdominis
The rectus abdominis is a long, flat muscle that extends along the whole length of the front of the abdomen. It is commonly referred to as the "abs muscle" and is visible as a "six-pack" in people with low body fat. The rectus abdominis is part of the abdominal muscle group, which also includes the transversus abdominis, internal and external obliques, and pyramidalis muscles. These muscles work together to form the anterolateral abdominal wall.
The rectus abdominis muscle is responsible for flexing the spinal column and tensing the anterior wall of the abdomen. It assists in compressing the contents of the abdomen, which helps to protect the abdominal viscera. This muscle also plays a role in respiration, particularly during forceful exhalation after exercise or in certain medical conditions.
The rectus abdominis originates from the pubic crest and pubic symphysis at the lower end. Its fibres extend vertically and insert into the xiphoid process of the sternum and the costal cartilages of the 5th to 7th ribs. In some cases, the most lateral fibres may attach to the 3rd and 4th ribs as well. The muscle is separated from its fellow on the opposite side by the linea alba, a connective tissue.
The rectus abdominis is innervated by the thoraco-abdominal nerves, which are continuations of the T7-T11 intercostal nerves. It receives its blood supply from several vessels, predominantly the inferior and superior epigastric arteries, as well as contributions from other arteries.
In terms of assessment and exercise, the strength of the rectus abdominis is typically evaluated rather than its flexibility. The sit-up exercise is commonly used to target this muscle, involving raising and lowering the trunk against gravity to the midline. To isolate the rectus abdominis, exercises can be performed with bent knees to minimise the engagement of hip flexors.
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Latissimus dorsi
The latissimus dorsi is a large, flat muscle that covers the back and stretches to the sides, behind the arm. The name "latissimus dorsi" comes from Latin and means "broadest of the back". It is the widest muscle in the human body, covering almost all back muscles at the posterior trunk, except the trapezius. The latissimus dorsi is also referred to as the "lats muscle", or simply "lats", especially among bodybuilders.
The latissimus dorsi is responsible for several functions, including extension, adduction, transverse extension (also known as horizontal abduction or horizontal extension), flexion from an extended position, and medial internal rotation of the shoulder joint. It also plays a role in the extension and lateral flexion of the lumbar spine, and assists in deep inspiration and forceful respiratory functions such as coughing and sneezing.
The latissimus dorsi is innervated by the sixth, seventh, and eighth cervical nerves through the thoracodorsal nerve (long subscapular nerve). It receives its blood supply primarily from the thoracodorsal artery, a branch of the subscapular artery, as well as contributions from the posterior intercostal arteries and lumbar arteries.
The latissimus dorsi is involved in movements of the arm and scapula. It can pull the inferior angle of the scapula in various directions, resulting in internal rotation, adduction, and extension of the arm. Additionally, when the arms are in a fixed overhead position, the latissimus dorsi pulls the trunk upward and forward, as in climbing or performing a chin-up.
The latissimus dorsi is a superficial muscle, found in the lower two-thirds of the trunk. It spans the lumbar and lower thoracic regions of the back and is attached to the dorsal vertebrae, with the number of attachments varying from four to eight. It is closely related to the teres major muscle, with which it shares a similar origin and works collaboratively to perform actions of the upper extremity.
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Oblique muscles
The torso, or trunk, is the central region of the body that connects the upper and lower extremities. It contains over 40 bones and 30 pairs of skeletal muscles. The torso muscles are divided into two large groups based on their location. The core muscles include muscles of the anterior and posterior torso, and the pelvis. The abdominal muscle group includes the transversus abdominis, internal and external obliques, and rectus abdominis.
The external oblique muscle is one of the outermost abdominal muscles, extending from the lower half of the ribs around and down to the pelvis. The internal obliques are underneath the external obliques on each side of the trunk. The external oblique is the largest and outermost of the three flat abdominal muscles of the lateral anterior abdomen. It is situated on the lateral and anterior parts of the abdomen and is broad, thin, and irregularly quadrilateral. The external oblique functions to pull the chest downwards and compress the abdominal cavity, increasing intra-abdominal pressure. It also performs ipsilateral side-bending and contralateral rotation: the right external oblique would side-bend to the right and rotate to the left, and vice versa.
The internal oblique muscle functions similarly to the external oblique, except it rotates ipsilaterally. Oblique strain is a common injury in baseball, particularly for pitchers, and can affect either the leading side external oblique or the trailing internal oblique.
The obliques are also known as the waist muscles, connecting the ribs, top of the hip bone, fascia of the abdominals, and lower back. They control bending movements such as bending over, twisting the torso, and side bending, and they assist with breathing. Bilateral contraction of the external oblique along with the rectus abdominis and internal oblique flexes the trunk by drawing the pubis towards the xiphoid, as in crunches or sit-ups.
Weakness in the external oblique can decrease the ability of trunk flexion, and trigger points can develop due to emotional stress, exercise load, or trauma. Oblique muscle pain can be acute or chronic and can be caused by activities such as rowing, raking leaves, coughing, lifting heavy loads, or even sitting for long periods. It is important to consult a doctor or physical therapist for persistent pain, as it can be a symptom of a serious medical condition.
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Frequently asked questions
The torso contains over 30 pairs of skeletal muscles, which are divided into two large groups based on their location. The anterior muscles of the torso are those on the front of the body, including the muscles of the chest, abdomen, and pelvis. The chest muscles function in respiration, while the abdominal muscles function in torso movement and in maintaining balance and posture. The rectus abdominis is a long, strap-like, paired muscle that acts as a flexor of the trunk. The obliques are abdominal muscles that assist during bending and twisting of the torso.
The primary functions of the muscles of the torso are to enable movement of the lumbar and thoracic spine, ribs, and proximal limbs, to facilitate breathing, and to protect the vital organs. The torso muscles also contribute to changing the intra-abdominal pressure, which is essential for basic bodily functions such as micturition and defecation.
The torso can be divided into the upper torso or thorax, and the lower torso, which includes the abdomen and pelvic areas. The torso can also be divided into the anterior and posterior regions. The core muscles of the torso include muscles of the anterior and posterior torso and the pelvis. The abdominal muscle group includes transversus abdominis, internal and external obliques, and rectus abdominis. The minor (peripheral) core muscles include trapezius, latissimus dorsi, and gluteus maximus.
