Logan Steele
The trunk of the body, or torso, is the central part of the body to which the head and limbs are attached. The trunk contains muscles of the head, chest, thoracic cavity, abdominal cavity, and pelvis. These muscles can be divided into anterior and posterior muscles. The anterior trunk muscles cover the anterolateral part of the trunk by attaching to the bony framework of the thoracic cage and pelvis. The posterior trunk muscles, commonly referred to as the muscles of the back, are divided into two functional groups: superficial (extrinsic) and deep (intrinsic).
| Characteristics | Values |
|---|---|
| Location | Front of the body, including the chest, abdomen, and pelvis |
| Composition | Four muscle pairs, arranged in layers, and the fascia that envelops them |
| Function | Movement of the vertebral column, formation of the thoracic and abdominal walls, and covering the pelvic outlet |
| Types of Muscles | Pectoral, intercostal, abdominal, pelvic, and back muscles |
| Example Muscles | Pectoralis major, pectoralis minor, serratus anterior, subclavius, internal and external intercostal, subcostal, transversus thoracis, rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, transversus abdominis, latissimus dorsi, trapezius, deltoid |
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What You'll Learn
The trunk includes the chest, abdominal, and pelvic regions
The trunk of the body is the central, main part of the body that houses all the internal organs. It includes the chest, abdominal, and pelvic regions. The trunk muscles are all the muscles of the axial skeleton. These include the muscles that move the vertebral column, the muscles that form the thoracic and abdominal walls, and those that cover the pelvic outlet. The trunk muscles are responsible for making and keeping the body erect, as well as sitting and standing up, and maintaining that posture.
The chest muscles are the first to be described, followed by the abdominal muscles. The chest muscles function in respiration, while the abdominal muscles function in torso movement and in maintaining balance and posture. The pectoral muscles lie in the chest and exert force through the shoulder to move the upper arm. The pectoralis major is a fan-shaped muscle covering the chest and is comprised of clavicular and sternocostal regions. The clavicular region originates from the clavicle, while the sternocostal region originates from the sternum and the fascia of the oblique muscles of the abdomen. Both attach to the humerus. The pectoralis major muscle 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 minor lies beneath the pectoralis major. It originates from the third to fifth ribs and attaches to the scapula. It functions to lower the scapula and support it.
The abdominal wall consists of four muscle pairs, arranged in layers, and the fascia that envelops them. There are five muscles that form the abdominal part of the anterior trunk. These are the rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, and transversus abdominis. The rectus abdominis is a long, strap-like, paired muscle that passes vertically over the entire length of the abdomen. It acts as a flexor of the trunk and an accessory muscle of expiration. It also compresses the abdominal contents to protect them. The rectus abdominis can sometimes be seen beneath the skin in athletic individuals, resulting in what’s commonly referred to as a ‘six-pack’. The external abdominal oblique and the internal oblique muscles are the most superficial, overlying the latter. The external oblique muscles originate from the external surfaces of ribs 5-12. The internal oblique muscles originate from the anterior two-thirds of the iliac crest, the iliopectineal arch, and the thoracolumbar fascia.
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The abdominal wall is made up of four muscle pairs
The abdominal wall is made up of several muscles, including five pairs of anterolateral muscles and three or four posterior muscles, depending on the individual. The abdominal wall is a vital structure that encases the abdominal cavity, containing and protecting the intra-abdominal organs. It also enables abdominal movements, such as flexion, extension, lateral flexion, and rotation.
The five pairs of anterolateral muscles are the external oblique, internal oblique, transversus abdominis, rectus abdominis, and pyramidalis. The external oblique is the outermost layer, with the internal oblique muscles underneath, and the rectus abdominis in between the internal obliques. The transversus abdominis is the deepest layer. These muscles work together to facilitate trunk movements and maintain stability.
The rectus abdominis is a long, strap-like, paired muscle that runs vertically down the middle of the abdomen, from the ribs to the pelvis. It is divided into two segments by the linea alba. This muscle acts as a flexor of the trunk and helps protect the abdominal contents. It can sometimes be visible in athletic individuals as a "six-pack."
The pyramidalis is a small, triangular muscle located at the base of the pubic bone in front of the rectus abdominis. It is a variable muscle, being absent in about 20% of the population.
The posterior abdominal wall is supported by the vertebrae and includes the psoas major, iliacus, quadratus lumborum, and, in about 40% of people, the psoas minor. These muscles contribute to movements and stability of the trunk.
The abdominal muscles, along with the back muscles, form the core muscles, providing stability and balance to the body.
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The chest muscles are involved in respiration
The trunk of the body is the central part of the torso, from the shoulders down to and including the abdominal area. The chest, or thoracic cage, is enclosed within the thoracic cavity, which is protected by the rib cage. The chest muscles are involved in respiration, which is defined as the movement of air between the atmosphere and the lung alveoli.
The chest muscles include the pectoralis major, pectoralis minor, serratus anterior, subclavius, intercostal (external, internal and innermost), subcostal and transversus thoracis muscles, including the diaphragm. The diaphragm is a sheet of muscle that contracts and pulls downward during inhalation, while the muscles between the ribs contract and pull upward. This increases the size of the thoracic cavity and decreases the pressure inside, allowing air to rush in and fill the lungs.
The primary inspiratory muscles are the diaphragm and external intercostals. The diaphragm lengthens and shortens the chest cavity, while the intercostals elevate the ribs and sternum. During forceful expiration, the internal intercostals, intercostalis intimi, subcostals and the abdominal muscles are used. The abdominal muscles include the rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique and transversus abdominis. The rectus abdominis, or "abs", is a long, strap-like, paired muscle that passes vertically over the entire length of the abdomen. The abdominal oblique muscles are the most superficial, overlying the internal oblique muscles, and they originate from the external surfaces of ribs 5-12.
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The abdominal muscles are involved in torso movement and posture
The abdominal muscles are essential for torso movement and maintaining posture. They are located between the ribs and the pelvis on the front of the body. These muscles, along with the back muscles, make up the core muscles, providing stability and balance to the body and protecting the spine. They are involved in regulating internal abdominal pressure, which is crucial for various bodily functions such as breathing, coughing, and defecation.
There are five main abdominal muscles: pyramidalis, rectus abdominis, external obliques, internal obliques, and transversus abdominis. The rectus abdominis is a long, strap-like muscle that runs down the middle of the abdomen, often associated with the "`six-pack`" appearance in fit individuals. It acts as a flexor of the trunk and an accessory muscle during expiration, and helps protect the abdominal contents. The external and internal oblique muscles are involved in trunk flexion, rotation, and compression of abdominal viscera. They also assist with expiration. The transversus abdominis is the deepest muscle layer, stabilising the trunk and maintaining internal abdominal pressure.
The abdominal muscles work in harmony with other muscle groups to control the movement of the spine, pelvis, and rib cage. They enable the torso to move during various activities such as walking, sitting, standing, and twisting. Additionally, these muscles play a vital role in holding organs in place, including the stomach, intestines, pancreas, liver, and gallbladder.
Abdominal muscle strains can occur due to overstretching, overuse, or violent or poorly executed movements. To prevent injuries, it is essential to incorporate proper warm-up and cool-down routines, maintain good form during sports, and regularly stretch.
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The back muscles allow for the movement of the shoulder, head, and neck
The trunk muscles are those that support the torso, allowing for movement and helping with breathing. They include the muscles of the thoracic cage, the abdominal wall, and the back.
The back muscles, in particular, allow for the movement of the shoulder, head, and neck. They are woven layers of groups that run from the neck, across the shoulders, and down the spine to the lower back, ending just above the hips. These muscles attach to bones across the body, including the vertebrae and shoulder blades.
The trapezius muscle, for example, starts at the neck, goes across the shoulders, and extends down to the lower back in a V shape. The levator scapulae are smaller muscles that start at the side of the neck and extend to the shoulder blades. The rhomboid muscles connect the shoulder blades to the spine.
The back muscles also include the latissimus dorsi, often referred to as the "lats," which extend from below the shoulder blades to the spine in the lower back. These muscles are the largest in the upper half of the body. The serratus anterior muscles cover the top of the rib cage, just below the armpits, and extend from the back, wrapping around the sides of the rib cage.
The back muscles work together to allow for movements such as bending over, twisting, turning the head, and extending the back. They also assist in breathing by expanding and contracting the chest during inhalation and exhalation. These movements are made possible by the contraction of skeletal muscles, which are attached to bones by tendons.
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Frequently asked questions
The trunk muscles are the muscles located in the central, main part of the body, also known as the torso. They include the chest, abdominal, and pelvic regions of the body.
The trunk muscles include the pectoral muscles, intercostal muscles, abdominal muscles, pelvic muscles, and back muscles.
The trunk muscles are responsible for maintaining posture, breathing, moving the upper portions of the body, such as the neck and head, and assisting in basic bodily functions such as micturition and defecation.
