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The torso, or trunk, is the central part of the body that connects the upper and lower extremities. It houses all the vital organs of the body, except the brain. The muscles of the torso can be divided into two large groups based on their location and function. The anterior trunk muscles cover the anterolateral part of the torso by attaching to the bony framework of the thoracic cage and pelvis. The posterior muscles include the trapezius, latissimus dorsi, and gluteus maximus. The torso muscles also include the abdominals, pectorals, erector spinae, serratus anterior and posterior, intercostals, and rhomboids. These muscles have several important functions, including supporting the body during movement, protecting the organs, and facilitating breathing.
| Characteristics | Values |
|---|---|
| Number of bones in the torso | 40 |
| Number of skeletal muscles in the torso | 30 pairs |
| Functions of the torso muscles | Enable movement of the lumbar and thoracic spine, ribs and proximal limbs, facilitate breathing, and protect the vital organs |
| Types of torso muscles | Abdominals, pectorals, erector spinae, serratus anterior and posterior, intercostals, latissimus dorsi, and rhomboids |
| Types of abdominal muscles | Pyramidalis, rectus abdominus, external obliques, internal obliques, and transversus abdominis |
| Functions of abdominal muscles | Holding organs in place, supporting the body during movement, posture, stability, and compression of organs during breathing and defecation |
| Torso muscle groups | Anterior and posterior torso, and the pelvis |
| Torso muscle subdivisions | Upper torso (thorax), lower torso (abdomen, pelvic and perineal segments) |
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What You'll Learn
Intercostal muscles
The intercostal muscles are a group of intrinsic rib cage muscles that occupy the 11 intercostal spaces between the ribs. They are divided into three groups, from superficial to deep: external, internal, and innermost intercostals. All three groups of muscles support the rib cage and are accessory respiratory muscles that participate in the process of forced breathing.
The external intercostal muscles, also known as intercostalis externus, aid in quiet and forced inhalation. They originate on ribs 1–11 and have their insertion on ribs 2–12. The muscle fibres are directed downwards, forwards, and medially in the anterior part. The function of these muscles is to elevate the ribs and bend them more open, thus expanding the transverse dimensions of the thoracic cavity.
The internal intercostal muscles, also known as intercostalis internus, aid in forced expiration. They originate on ribs 2–12 and have their insertions on ribs 1–11. Their fibres pass anterior and superior from the upper margin of the rib and costal cartilage to the low. The internal intercostals are responsible for the depression of the ribs and bending them inward, thus decreasing the transverse dimensions of the thoracic cavity.
The innermost intercostal muscles, also known as intercostalis intimus, are deep layers of the internal intercostal muscles, separated from them by a neurovascular bundle. They originate from the costal groove of one rib, posteriorly to the origin of the internal intercostals. The muscle fibres are directed downwards, forwards, and laterally, similar to the intercostalis internus muscle.
Intercostal muscle strain can occur due to weakened muscles, overexertion, direct trauma, or repetitive torso twisting. Symptoms include pain in the upper back or rib cage, muscle tension and stiffness, and worsening pain within days or weeks.
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Subcostal muscles
The subcostal muscles are a group of muscles of the thorax, consisting of short, individual skeletal muscles found in the lower half of the posterior thoracic wall. They are strips of muscle located on the internal surface of the lower ribs, sharing a plane with the innermost intercostals. The subcostal muscles originate from the internal surfaces of the seventh to tenth ribs, in the areas located adjacent to the angles of these ribs.
The fibres of the subcostal muscles travel inferomedially and insert onto the second rib that is inferior to their origin sites (i.e. the ninth to twelfth ribs). They insert onto the areas located adjacent to the angles of these ribs. There can be variations between individuals regarding the origin sites for the subcostal muscles.
The subcostales (singular: subcostalis) consist of muscular and aponeurotic fasciculi, which are usually well-developed only in the lower part of the thorax. Each subcostalis originates from the inner surface of one rib and is inserted into the inner surface of the second or third rib below, near its angle. Their fibres run in the same direction as those of the intercostales interni.
The subcostal muscles depress the ribs at their costovertebral joints, assisting in expiration. They support the intercostal spaces and thoracic cage, and depress the ribs during forced expiration. They receive innervation from the intercostal nerves.
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Abdominal muscles
The torso, or trunk, is the central region of the body that connects the upper and lower extremities. The trunk houses all the vital organs of the human body except the brain. The muscles of the torso are divided into two large groups based on their location: the anterior trunk muscles and the posterior trunk muscles. 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 abdominal muscles are a group of five main muscles that support the trunk and allow movement. They are located between the rib cage and the pelvis on the front of the body. The abdominal muscles work together with the back muscles to form the core muscles, which help protect the spine and keep the body stable and balanced. These muscles also help to regulate internal abdominal pressure, which is important for essential bodily functions such as breathing, coughing, vomiting, and childbirth.
The abdominal muscle group includes the transversus abdominis, internal and external obliques, and rectus abdominis. The transversus abdominis is the deepest muscle layer and its main roles are to stabilise the trunk and maintain internal abdominal pressure. The rectus abdominis is slung between the ribs and the pubis at the front of the pelvis, and its contraction creates the characteristic bumps or bulges commonly called "the six-pack". The external oblique muscles allow the trunk to twist, while the internal oblique muscles operate in the opposite direction, with the left and right sides contracting together to twist the trunk.
Abdominal muscle strains are a common condition affecting the abdominal muscles, caused by overstretching, overuse, or violent twisting of the trunk. These strains can range from minor tears in the muscle fibres to severe pulls that detach the muscle. Another health issue involving the abdominal muscles is a hernia, where an internal organ pushes through a weak spot in the muscle. Prune belly syndrome is a rare condition where a newborn has absent or weak abdominal wall muscles, resulting in a wrinkled abdomen.
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Back muscles
The torso, or trunk, is the central area of the human body, housing all vital organs except the brain. The muscles of the torso are divided into two large groups, depending on their location: the anterior trunk muscles and the posterior trunk muscles. 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 back muscles are a part of the posterior trunk muscles and can be categorised into three groups based on their location: superficial back muscles, intermediate back muscles, and intrinsic back muscles. These muscles start just under the skull, go across the shoulders, and run down the spine to just above the hips. They attach to bones across the body, including the vertebrae, and help control posture, movement, and breathing.
The superficial back muscles are found just under the skin and include the latissimus dorsi, trapezius, levator scapulae, and rhomboids. These muscles originate at the vertebral column and insert onto either the clavicle, scapula, or humerus, allowing movement at the shoulder.
The intermediate back muscles work to elevate and depress the rib cage.
The intrinsic back muscles, also called true back muscles, are located deep within the body, separated from the extrinsic muscles by the thoracolumbar fascia. These muscles help with flexion/extension, rotation, and side bending of the back, as well as locomotor function and assistance in breathing.
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Pelvic and hip muscles
The torso, or trunk, is the central area of the human body, containing over 30 pairs of skeletal muscles. The torso can be divided into the upper and lower torso, with the latter including the abdomen and pelvic areas. The pelvic and hip muscles are a part of the lower torso and play a crucial role in stabilising the pelvis and enabling movement.
The hip muscles can be divided into three main groups: the iliopsoas group, the inner hip muscles, and the large and superficial gluteal muscles. The iliopsoas group includes the iliacus, psoas major, and psoas minor muscles. These muscles originate from the posterior abdominal wall and insert at the lesser trochanter of the femur, crossing the hip joint. The psoas major and iliacus muscles also contribute to flexing the trunk. The psoas minor is only present in about 40% of people.
The inner hip muscles, also known as deep external rotators, include the piriformis, obturator internus, obturator externus, gemellus superior, gemellus inferior, and quadratus femoris. These muscles play a crucial role in stabilising the pelvis and externally rotating the thigh at the hip joint.
The large and superficial gluteal muscles include the gluteus maximus, gluteus medius, gluteus minimus, and tensor fasciae latae. These muscles have a variety of functions, including extension, external and internal rotation, and abduction and adduction of the thigh at the hip joint. The gluteal muscles are innervated by the superior and inferior gluteal nerves, with the exception of the gluteus maximus, which is innervated by the inferior gluteal nerve.
The pelvic and hip muscles are essential for maintaining balance and facilitating movement, including walking. They also contribute to protecting the vital organs located within the torso.
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Frequently asked questions
The torso muscles are responsible for essential body activities such as breathing, movement, defecation and micturition. They also enable movement of the lumbar and thoracic spine, ribs and proximal limbs, and facilitate breathing and protection of the vital organs.
The torso muscles can be divided into two large groups based on their location and function. The anterior trunk muscles cover the anterolateral part of the trunk and attach to the bony framework of the thoracic cage and pelvis. The abdominal muscles include the rectus abdominis, internal and external obliques, pyramidalis, and transversus abdominis. The minor (peripheral) core muscles include the trapezius, latissimus dorsi, and gluteus maximus.
Intercostal muscles are a group of three layered muscles found in the intercostal spaces between the ribs. They support the intercostal spaces and thoracic cage. The external intercostals elevate the ribs during forced inspiration, expanding the thorax and lungs.
Subcostal muscles are strips of muscle located on the internal surface of the lower ribs. They support the intercostal spaces and thoracic cage, and depress the ribs during forced expiration.
