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The trunk, or torso, is the central part of the body to which the head and limbs are attached. The trunk muscles are divided into two large groups based on their location: the anterior trunk muscles and the muscles of the thoracic cage. The trunk muscles are responsible for several essential body activities, including breathing, movement, defecation, and micturition. The diaphragm, a dome-shaped muscle that separates the thoracic and abdominal cavities, is crucial for respiration. The abdominal wall muscles, including the rectus abdominis, play a role in movements like flexion and rotation. Superficial back muscles, such as the latissimus dorsi and trapezius, help with shoulder movement and provide support for the torso. Understanding the structure and function of these muscles is essential for maintaining posture, facilitating movement, and preventing injuries.
| Characteristics | Values |
|---|---|
| Muscles of the trunk | Rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, transversus abdominis, latissimus dorsi, levator scapulae, rhomboids, trapezius, serratus anterior, intercostal, diaphragm |
| Function | Support the spine and trunk, help maintain posture, enable movement, assist in breathing |
| Lateral flexion of the torso | Internal and external obliques, quadratus lumborum, erector spinae, rectus abdominis, iliopsoas, semispinalis |
| Treatment for lateral trunk flexion | Muscle energy techniques (MET), isometric contraction, stretching |
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What You'll Learn
- The diaphragm, a dome-shaped muscle, facilitates breathing and separates the thorax and abdomen
- The rectus abdominis, a long, strap-like muscle, passes over the abdomen
- The latissimus dorsi, the largest upper-body muscles, extend from the shoulder blades to the lower back
- The levator scapulae, which start at the neck and extend to the shoulder blades
- The internal and external obliques, which bend the torso sideways
The diaphragm, a dome-shaped muscle, facilitates breathing and separates the thorax and abdomen
The trunk, or torso, is the central part of the body to which the head and limbs are attached. The trunk muscles are divided into two large groups depending on their location: the anterior trunk muscles and the muscles of the thoracic cage. The diaphragm is a large, dome-shaped muscle located within the trunk. It separates the thorax and abdomen, facilitating breathing and supporting the thoracic cage.
The diaphragm consists of three parts: the sternal, costal, and lumbar parts. The sternal part originates from the posterior aspect of the xiphoid process, while the costal part arises from the internal surfaces of the lower costal cartilages and ribs 7-12. The lumbar part, on the other hand, originates from the bodies of vertebrae L1-L3, intervertebral discs, and various ligaments. These fibres converge on a central tendon in the middle of the trunk, which lacks bony insertions.
As the main muscle of breathing, the diaphragm is responsible for inspiration. It depresses the costal cartilages and receives innervation from the phrenic nerve (C3-C5). Additionally, the diaphragm facilitates the passage of anatomical structures through openings called hiatuses.
The diaphragm is an essential muscle for respiration and plays a crucial role in supporting the thoracic cage. The trunk muscles, including the diaphragm, contribute to protecting the thoracic and abdominopelvic viscera and assisting with essential body activities such as breathing, movement, defecation, and micturition.
Other muscles involved in trunk movement include the rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, and transversus abdominis. These muscles form the anterolateral boundary of the abdominal cavity and contribute to movements like flexion and rotation. They also play a role in changing intra-abdominal pressure, which is vital for basic bodily functions.
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The rectus abdominis, a long, strap-like muscle, passes over the abdomen
The trunk, or torso, is the central part of the body to which the head and limbs are attached. The trunk muscles are divided into two large groups, depending on their location: the muscles of the thoracic cage and the muscles of the abdominal wall. The thoracic cage is protected by the bony framework of the thoracic cage and pelvis. The abdominal wall, on the other hand, has no bony reinforcements or protection. Instead, the wall consists of four muscle pairs, arranged in layers, and the fascia that envelops them.
The rectus abdominis is a long, strap-like muscle that passes vertically over the entire length of the abdomen. It is one of the five muscles that form the abdominal part of the anterior trunk, along with the pyramidalis, external abdominal oblique, internal abdominal oblique, and transversus abdominis. These muscles are involved in movements of the trunk, mainly flexion and rotation. They also contribute to changing the intra-abdominal pressure, which is essential for basic bodily functions such as micturition and defecation.
The rectus abdominis is a paired muscle, meaning it has two sides that work together to produce movement. When the rectus abdominis contracts, it flexes the trunk. This can be felt when performing an abdominal crunch, where the front of the body is shortened and rounded forward. It is important to balance this movement with other actions to avoid overworking the muscle.
The rectus abdominis also assists with lateral flexion of the torso. When the muscles on one side of the body contract, the torso bends to that side. For example, when the right rectus abdominis contracts, the body bends to the right. This movement is also facilitated by other muscles, including the internal and external obliques, quadratus lumborum, and erector spinae.
The rectus abdominis plays a crucial role in maintaining core stability and supporting the torso. By contracting and relaxing in coordination with other trunk muscles, it enables various movements and contributes to essential bodily functions.
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The latissimus dorsi, the largest upper-body muscles, extend from the shoulder blades to the lower back
The latissimus dorsi is a large, flat muscle in the lower thorax, extending from the shoulder blades to the lower back. It is the largest upper-body muscle and is commonly known as "lats", especially among bodybuilders. The latissimus dorsi muscle originates from several locations, including the spinous processes of vertebrae T7-L5, the thoracolumbar fascia, posterior iliac crest, lower third or fourth ribs, and the inferior angle of the scapula. The muscle fibres extend towards the axilla, wrapping around the teres major muscle.
The primary function of the latissimus dorsi is to move the upper extremity, but it also assists in depression of the arm with the teres major and pectoralis major muscles. It adducts, extends, and internally rotates the shoulder and arm. The latissimus dorsi is also active during deep inspiration and forceful respiratory functions such as coughing and sneezing.
The latissimus dorsi plays a role in the extension and lateral flexion of the lumbar spine. It has a synergistic role in extension (posterior fibres) and lateral flexion (anterior fibres) of the lumbar spine. The muscle is active in moving the trunk anterior and superior when the upper extremities are fixed overhead, as in climbing or performing a chin-up.
Injuries to the latissimus dorsi are rare but can occur due to overuse, poor posture, or poor form in sports and exercise. It can be injured during exercises such as pull-ups and bench presses. Specific sports that can increase the risk of injury include golf, baseball, swimming, skiing, rowing, tennis, and swimming. Tightness in the latissimus dorsi can also contribute to chronic shoulder and back pain.
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The levator scapulae, which start at the neck and extend to the shoulder blades
The trunk, or torso, is the central part of the body to which the head and limbs are attached. The trunk muscles are divided into two large groups depending on their location: the muscles of the thoracic cage and the muscles of the abdominal wall. The diaphragm, a dome-shaped muscle located within the trunk, is the main muscle of breathing and facilitates inspiration.
The levator scapulae is a long and slender muscle that belongs to the superficial layer of extrinsic muscles of the back. It is located in the neck and shoulder region and is prone to stiffening and chronic pain due to poor posture in everyday life. Common causes include carrying heavy shoulder bags, permanently lifting the shoulders while sitting at a desk, and sleeping on one side of the body without proper head support.
The levator scapulae muscle is innervated by the anterior rami of spinal nerves C3 and C4 and the dorsal scapular nerve (C5), a branch of the brachial plexus. A large portion of the muscle is vascularized by two branches of the thyrocervical trunk: the transverse cervical and ascending cervical arteries. Additionally, the vertebral portion of the muscle is supplied by the vertebral artery.
The main function of the levator scapulae is to elevate and retract the shoulder girdle at the scapulothoracic joint. It also helps to form the floor of the posterior triangle of the neck. When the scapula is fixed, contraction of the levator scapulae leads to the lateral flexion of the cervical vertebral column and stabilizes the vertebral column during rotation. If the cervical spine is fixed, this muscle helps in elevating and rotating the scapula, moving the lateral angle inferiorly. Bilateral contraction assists in the extension of the cervical spine.
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The internal and external obliques, which bend the torso sideways
The torso, or trunk, is the central part of the body to which the head and limbs are attached. The torso muscles attach to the skeletal core of the trunk and are divided into two large groups depending on their location. These muscles support the spine and trunk, help the body maintain its posture, and assist with essential bodily functions such as breathing, movement, defecation, and micturition.
The internal and external obliques are muscles that bend the torso or trunk sideways. They are part of the abdominal wall muscles, which also include the rectus abdominis, pyramidalis, and transversus abdominis. The internal and external obliques are hard to differentiate, even though they perform slightly different movements. The obliques are also involved in rotating the torso. When the muscles on one side of the torso contract, the torso bends to that side. For example, when the muscles on the right side of the body contract, the torso bends to the right.
The internal and external obliques are located near the midline of the body, along with the rectus abdominis and pyramidalis. These four muscles are classified as vertical muscles. The transversus abdominis is a flat muscle located more laterally. Together, these five muscles form the anterolateral boundary of the abdominal cavity. They are involved in movements of the trunk, mainly flexion and rotation, and they contribute to changing the intra-abdominal pressure, which is essential for basic bodily functions.
To strengthen the internal and external obliques, it is important to focus on movements that target these muscles. Crunches are not the best way to strengthen the core muscles, including the obliques. Instead, it is recommended to focus on stability and awareness of the core by hugging the waist. Additionally, yoga can be a great way to work the obliques and other core muscles, as long as the practice includes a balanced range of directional movements of the spine.
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Frequently asked questions
The trunk, or torso, is supported by back muscles. The primary muscles involved in lateral flexion of the torso are the internal and external obliques, the quadratus lumborum, and the erector spinae. The rectus abdominis, iliopsoas, and semispinalis assist with the movement.
The rectus abdominis is a long, strap-like, paired muscle that passes vertically over the entire length of the abdomen. It is responsible for flexing the trunk.
The diaphragm is a dome-shaped muscle that separates the thoracic and abdominal cavities. It is the main muscle of breathing and is responsible for inspiration.
Superficial back muscles are those closest to the surface, just under the skin. Examples include the latissimus dorsi (or "lats"), levator scapulae, rhomboids, trapezius, and serratus anterior.
A yoga practice that targets the trunk muscles is the Cobra pose.
