Dominic Stone
The torso, or trunk, is the central area of the body, containing over 30 pairs of skeletal muscles and all of the body's vital organs except the brain. The torso muscles are divided into two groups based on their location: the anterior trunk muscles and the posterior trunk muscles. The back muscles support the torso, enabling movement and assisting with breathing. The abdominal muscles, which are part of the core muscles, also help with movement and protect the internal organs. The erector spinae group of muscles is responsible for extending the vertebral column to maintain posture.
| Characteristics | Values |
|---|---|
| Number of bones in the torso | 40 |
| Number of pairs of skeletal muscles in the torso | 30 |
| Torso muscles | Abdominals, Pectorals, Erector Spinae, Serratus Anterior and Posterior, Intercostals, Latissimus Dorsi, Rhomboids, Trapezius, Levator Scapulae, Transversus Abdominis, Internal and External Obliques, Rectus Abdominis, Pyramidalis, Gluteus Maximus |
| Functions of torso muscles | Protection of thoracic and abdominopelvic viscera, breathing, movement, defecation, micturition, holding internal organs in place, supporting the spine and trunk, maintaining posture and balance |
| Torso regions | Upper torso (thorax), lower torso (abdomen and pelvic areas), anterior torso, posterior torso |
| Torso muscle groups | Anterior and posterior torso, pelvis, abdominal muscle group, erector spinae group, minor (peripheral) core muscles |
| Back muscles | Latissimus dorsi, Levator scapulae, Rhomboids, Trapezius, Serratus anterior, Serratus posterior superior, Intermediate back muscles |
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What You'll Learn
Erector spinae muscles
The erector spinae muscles are a group of muscles that play a crucial role in spinal stability and posture control. They are one of the core and paraspinal muscles, forming the intermediate layer of the deep, intrinsic muscles of the back. These muscles extend on either side of the vertebral column, from the base of the cranium to the pelvis.
The erector spinae muscles are divided into three groups, from medial to lateral: spinalis, longissimus, and iliocostalis. The spinalis muscles are the most medial and are further divided into three regional groups: spinalis capitis, spinalis colli, and spinalis thoracis. These muscles help extend and laterally flex the cervical and thoracic regions of the spine.
The longissimus muscles are the central and thickest erector spinae muscles. Similar to the spinalis muscles, they are also divided into three regional groups: longissimus capitis, longissimus colli, and longissimus thoracis. The longissimus muscles function to extend and laterally flex the spine and help rotate the head.
The iliocostalis muscles are the most lateral erector spinae muscles. They have three different insertions: iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis. The tightness in the iliocostalis muscles can affect the position of the hip and rib cage.
The erector spinae muscles are essential for maintaining spinal stability and preventing low back pain. In healthy individuals, these muscles relax in a range from an upright position to full lumbar flexion, contributing to spinal stability. However, in individuals with low back pain, the erector spinae muscles may become overactive, increasing the compression load on the vertebral column and potentially raising the risk of injury.
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Latissimus dorsi muscles
The latissimus dorsi is a large, flat muscle that covers the width of the middle and lower back. It is one of the largest muscles in the back and is commonly known as the "lats", especially among bodybuilders. The name "latissimus dorsi" comes from Latin and means "broadest of the back". This pair of muscles stretches to the sides, behind the arm, and is partly covered by the trapezius on the back near the midline.
The latissimus dorsi has many functions. It helps the chest expand during breathing and assists with many upper body and arm movements. It is responsible for 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. The latissimus dorsi also assists in depression of the arm and pulls the trunk upward and forward when the arms are in a fixed overhead position.
The latissimus dorsi can become injured through overuse, repetitive motions, or improper technique during exercise. Latissimus dorsi pain can manifest as discomfort or pain in the lat muscles, which span each side of the back. The pain may be widespread or affect only a specific part of the muscle, and it may worsen when a person uses the muscle, such as by extending their hands out in front of them or raising their hands above their head.
To relieve latissimus dorsi pain, it is important to rest the affected area and consult a healthcare professional for advice. Certain stretches and exercises can help ease the pain and strengthen the muscle to prevent further injury. For example, a person can try a yoga pose by beginning on all fours, bending their knees, and lowering their torso over their thighs while keeping their arms extended in front.
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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. During forced inspiration, these muscles elevate the ribs and bend them open, expanding the thoracic cavity. The muscle fibres are directed downwards, forwards, and medially in the anterior part.
The internal intercostal muscles, or intercostalis internus, assist in forced expiration. They originate on ribs 2–12 and insert on ribs 1–11. These muscles are responsible for depressing the ribs and bending them inward, reducing the size of the thoracic cavity. Their muscle fibres are directed downwards, forwards, and laterally, forming a right angle with the external intercostal muscle.
The innermost intercostal muscles, also referred to as intercostalis intimus, are the deepest layer of intercostal muscles. They originate from the costal groove of one rib and insert onto the superior border of the rib below. The innermost intercostal muscles assist the internal and external intercostals in their functions.
Intercostal muscle strains can occur due to overexertion, direct trauma, or repetitive torso twisting. Symptoms of a strain include pain, muscle tension and stiffness, and difficulty breathing due to pain. Treatment and diagnosis are based on patient history and physical examination, and imaging techniques such as X-rays or MRIs may be used to rule out more serious injuries.
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Abdominal muscles
The abdominal muscles are a vital part of the human body, providing support and stability to the torso or trunk, which is the central area of the body. The trunk houses all the vital organs of the body, except the brain. The abdominal muscles are strong bands of muscles lining the walls of the abdomen, located between the rib cage and the pelvis at the front of the body. They are essential for holding internal organs in place and protecting them.
There are five main abdominal muscles: pyramidalis, rectus abdominus, external obliques, internal obliques, and transversus abdominis. These muscles work together to support the body during movement and help maintain posture. The rectus abdominis, for example, holds the internal organs in place and keeps the body stable during movement. It may form what is commonly known as a ""six-pack" when an individual has a trim and fit abdomen. The pyramidalis is a small, triangular-shaped vertical muscle located at the base of the pubic bone.
The abdominal muscles can be broadly divided into two walls: the anterolateral and the posterior. The anterolateral abdominal wall muscles consist of two vertical muscles (rectus abdominis and pyramidalis) and three flat muscles (external abdominal oblique, internal abdominal oblique, and transversus abdominis) stacked on top of each other towards the sides of the trunk. These muscles assist in breathing, movement, defecation, and micturition. They also help regulate internal pressure in the abdomen during essential bodily functions such as breathing, coughing, vomiting, and childbirth.
Abdominal muscle strains can occur due to overstretching, improper technique in sports, heavy lifting, or even activities like laughing, coughing, or sneezing. Treatment of abdominal muscle injuries can be challenging, as it is difficult to fully rest these muscles. However, gentle stretching and ice application can aid in the healing process.
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Subcostal muscles
The subcostal muscles are thin strips of muscle located on the internal surface of the lower ribs, sharing a plane with the innermost intercostals. They originate from the inner surface of one rib near its posterior angle and are inserted into the inner surface of the second or third rib below. The fibres of the subcostal muscles travel inferomedially, in the same direction as the intercostales interni.
The function of the subcostal muscles is to assist in respiration by depressing the ribs during forced exhalation, pulling them towards the central axis of the thorax, which compresses the lungs and pushes the air out. They also support the intercostal spaces and thoracic cage.
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Frequently asked questions
The torso contains over 30 pairs of skeletal muscles, including the abdominals, pectorals, erector spinae, serratus anterior and posterior, intercostals, latissimus dorsi, and rhomboids.
The muscles of the torso enable movement of the lumbar and thoracic spine, ribs, and proximal limbs, facilitate breathing, and protect the vital organs.
The erector spinae group of muscles, which extend from the sacrum to the skull, is responsible for extending the vertebral column to maintain erect posture. The latissimus dorsi muscles, also known as "lats," are the largest muscles in the upper half of the body, starting below the shoulder blades and extending to the spine in the lower back.
