Dominic Stone
Trunk muscles are those that form the central part of the human body, including the thorax and abdomen, and extending the neck and limbs. The anterior muscles of the trunk are associated with the front of the body and include chest and abdominal muscles. Chest muscles function in respiration, while abdominal muscles function in torso movement and in maintaining balance and posture. The muscles of the posterior portion of the trunk include muscles of the back, suboccipital region, and perineum region.
| Characteristics | Values |
|---|---|
| Definition | Muscles that form the central part of the human body, extending the neck and limbs, including the thorax and abdomen |
| Location | Anterior (front) and posterior (back) muscles of the torso |
| Function | Flexing and rotating the trunk, fixing and depressing the ribs, stabilising the pelvis, increasing intra-abdominal pressure, aiding in respiration, maintaining posture and balance |
| Types | Anterior: Pectoralis Major, Pectoralis Minor, Intercostal, Oblique, Rectus Abdominis, Transversus Abdominis, Serratus Anterior; Posterior: Latissimus Dorsi, Iliocostalis, Longissimus Dorsi, Multifidus, Quadratus Lumborum, Iliopsoas |
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What You'll Learn
The chest, abdomen, and pelvis
The trunk muscles of the torso are divided into anterior muscles, which are associated with the front of the body, and posterior muscles, which are associated with the back of the body.
Chest
The chest muscles, or pectoral muscles, function in respiration 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 pectoralis minor is a smaller muscle that lies beneath the pectoralis major. The intercostal muscles are deep muscles of the chest and front of the arm, with the boundaries of the axilla. They are the muscles between the ribs that form the chest cavity wall. The external intercostals are the most superficial of the intercostal muscles, while the internal intercostals lie below the external intercostals. The innermost intercostals are the deepest-lying of the intercostals and are similar in structure to the internal intercostals.
Abdomen
The abdominal muscles function in torso movement and in maintaining balance and posture. The obliques are abdominal muscles that assist during bending and twisting of the torso. The rectus abdominis, also known as the "abs" or "six-pack", are involved in numerous aspects of trunk stabilization and bending. The external oblique muscle is the outer layer of the abdominal muscles, with its aponeurosis covering the medial abdomen. Under the external oblique are the internal obliques on the sides of the abdomen and the rectus abdominis muscle in between. The deepest layer has the transverse abdominis muscle, whose fibres run laterally and are concentrated on the sides of the abdomen.
Pelvis
The serratus anterior muscle extends from the back and wraps around the sides of the rib cage. The multifidus is a group of muscles that work bilaterally to extend the spine and unilaterally to laterally flex the spine.
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The latissimus dorsi
The number of dorsal vertebrae to which the latissimus dorsi is attached varies from four to eight, and the number of costal attachments varies. The muscle's primary function is in the upper extremity, but it is also considered to be a respiratory accessory muscle. It assists in holding the scapula against the thorax during upper limb movements. The attachment of the muscle to the inferior angle of the scapula allows this. In activities such as walking with crutches, where the humerus becomes the fixed point when standing, the latissimus dorsi has the ability to pull the trunk forwards relative to the arms.
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The obliques
The external oblique muscles have two sets of fibres, which cover the left and right abdomen and are connected by a wide aponeurosis sheet in the centre of the abdomen. The internal oblique muscles lie underneath the external oblique muscles on each side of the trunk. The fibres of the internal obliques run up at an angle, in the opposite direction to the fibre angle of the external obliques. The internal oblique muscles function similarly to the external oblique muscles, except they rotate ipsilaterally (on the same side).
The external oblique muscles function to pull the chest downwards and compress the abdominal cavity, increasing intra-abdominal pressure. This compression of the abdominal cavity is important for movements such as the Valsalva manoeuvre. The external oblique muscles also perform ipsilateral (same side) side-bending and contralateral (opposite side) rotation: the right external oblique would side-bend to the right and rotate to the left, and vice versa.
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The rectus abdominis
In terms of assessment and grading, the strength of the rectus abdominis is typically evaluated rather than its flexibility. A common exercise for testing and strengthening this muscle is the sit-up, which involves raising the trunk against gravity to the midline and then slowly lowering it down in multiple sets. Maintaining strong abdominal muscles is important to prevent a range of problems, including spinal issues that can arise from weak core muscles.
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The multifidus
The main function of the multifidus muscle is to stabilise the lumbar spine. It also helps extend the lower spine during reaching or stretching. When the multifidus contracts bilaterally, it extends the spine, while unilateral contraction aids lateral flexion of the spine to the same side and rotation to the opposite side. The multifidus muscle also co-contracts with the transversus abdominis, providing stability around the entire torso, including the abdomen and lower back.
Weak or atrophied multifidus muscles can cause back pain and other back-related problems, such as herniated discs. Strengthening the core muscles helps to strengthen the multifidus muscle. Dry needling of the multifidus trigger points has been shown to increase the thickness of the transversus abdominis during contraction, suggesting that this treatment can be used to address low back pain.
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Frequently asked questions
Trunk muscles are those that form the central part of the human body, extending the neck and limbs, including the thorax and abdomen.
The anterior muscles of the trunk are associated with the front of the body and include chest and abdominal muscles.
The posterior muscles of the trunk include muscles of the back, suboccipital region, and perineum region.
Anterior trunk muscles include the intercostal muscles, which are deep muscles of the chest and front of the arm, and the pectoralis major and minor muscles. Posterior trunk muscles include the latissimus dorsi, which covers most of the lower back, and the trapezius muscle, which covers the upper back.
