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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 depending on their location. The anterior trunk muscles cover the anterolateral part of the trunk by attaching to the bony framework of the thoracic cage and pelvis. The muscles of the trunk include those that move the vertebral column, those that form the thoracic and abdominal walls, and those that cover the pelvic outlet. The erector spinae group of muscles on each side of the vertebral column is a large muscle mass that extends from the sacrum to the skull. These muscles are responsible for extending the vertebral column to maintain an erect posture. Trunk muscle strength is important in assessing the muscular unbalance that can cause low back pain.
| Characteristics | Values |
|---|---|
| Definition | Trunk extensors are muscles that play a role in extending the vertebral column to maintain erect posture. |
| Function | Extensors assist in essential body activities such as breathing, movement, defecation, and micturition. |
| Muscles Involved | Erector spinae, intercostal muscles, rectus abdominis, pyramidalis, external abdominal oblique, internal abdominal oblique, transversus abdominis, pectoralis major, pectoralis minor, serratus anterior, subclavius, subcostal, transversus thoracis, diaphragm. |
| Strength Evaluation | Trunk muscle strength evaluations are important to prevent problems like low back pain and dysfunction. |
| Gender Differences | Studies suggest that men generally exhibit higher trunk extensor strength values than women. |
| Age Differences | Age appears to be a factor in trunk muscle strength, with older adults experiencing pain and altered muscle activation patterns. |
| Training Exercises | Back- and hip-extension exercises, such as bridging and diagonal hip and shoulder extension, can activate trunk extensor muscles. |
| Measurement Techniques | Surface electromyography (EMG) is used to quantitatively measure muscle activation levels and patterns during movement. |
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What You'll Learn
Erector spinae muscles extend the vertebral column
The erector spinae muscles are a group of muscles that run vertically on either side of the spine, extending from the sacrum to the skull. They are one of the core and paraspinal muscles and are responsible for extending the vertebral column and maintaining erect posture. The erector spinae are divided into three groups, from medial to lateral: the spinalis, longissimus, and iliocostalis muscles.
The spinalis muscles are the most medial erector spinae muscles and are innervated by the lateral branches of the posterior rami of the cervical, thoracic, and lumbar spinal nerves. These muscles function to extend and laterally flex the cervical and thoracic regions of the spine. The longissimus muscles are the central and thickest erector spinae muscles. They are divided into three regional groups, similar to the spinalis muscles, and originate from the transverse processes of the vertebrae. The iliocostalis muscles are the most lateral part of the erector spinae and attach to the ribs. Due to their lateral position, tightness in the iliocostalis muscles can affect the position of the hip and rib cage.
The erector spinae muscles work together to bilaterally extend the vertebral column and unilaterally cause lateral flexion. They also help to maintain posture by stabilising the spine on the pelvis during walking. In addition, the erector spinae muscles can compensate for decreased activity and atrophy of the multifidus muscle in patients with low back pain, stabilising the lumbar spine. However, this increased activity can also increase the compression load on the vertebral column, potentially increasing the risk of injury.
The erector spinae muscles are the most superficial of the posterior trunk muscles and are susceptible to back strains. Back strains can occur when there is an incorrect balancing of a load on the vertebral column, placing strain on the muscles. To prevent back strains and pain, it is important to focus on lifting with the knees rather than the back and to perform exercises that increase the muscle tone of the erector spinae, such as adequate warm-up, stretching, and back exercises.
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Intercostal muscles aid breathing
The trunk (torso) is the central part of the body to which the head and limbs are attached. The trunk houses all the vital organs of the human body, except for the brain. The muscles of the trunk include those that move the vertebral column, form the thoracic and abdominal walls, and cover the pelvic outlet.
The intercostal muscles are located in the spaces between the ribs. They are involved in breathing and form two thin layers that span each of the intercostal spaces. The outer layer, the external intercostals, extends from the tubercles of the ribs. The external intercostals aid inspiration by lifting and expanding the rib cage, allowing for exhalation. The internal intercostals, on the other hand, pull down on the rib cage, thereby pushing air out of the lungs. They are the most important respiratory muscles for normal speech and singing, as they propel air out through the mouth and nose. The greater the pressure of the escaping air, the louder one's voice.
The mechanical advantages of the external and internal intercostals depend partly on the orientation of the muscle but mostly on interspace number and the position of the muscle within each interspace. The external intercostals in the dorsal portion of the rostral interspaces have a large inspiratory mechanical advantage. However, this advantage decreases ventrally and caudally, and in the ventral portion of the caudal interspaces, it is reversed into an expiratory mechanical advantage.
The internal interosseous intercostals in the caudal interspaces also have a large expiratory mechanical advantage, but this decreases cranially and ventrally in the upper interspaces. The intercartilaginous portion of the internal intercostals (parasternal intercostals) has an inspiratory mechanical advantage, while the triangularis sterni has a large expiratory mechanical advantage.
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Abdominal muscles enable trunk flexion
The trunk (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 cover the anterolateral part of the trunk by attaching to the bony framework of the thoracic cage and pelvis. The abdominal muscles are a part of the anterior trunk.
The abdominal 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.
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 first three are classified as vertical muscles and are located near the midline. The remaining ones are flat muscles and are located more laterally.
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 abdominal oblique muscles are involved in trunk flexion and ipsilateral rotation, as well as compression of abdominal viscera. They also assist with expiration. The external oblique muscles originate from the external surfaces of ribs 5-12, while 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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Back extensors are strengthened by exercise
The back extensors are a group of muscles responsible for extending the back and controlling the spine's flexibility. They include the erector spinae, which run from the sacrum to the skull, and the quadratus lumborum, the deepest back muscle, extending from the lowest rib to the pelvic bone. Strengthening these muscles is important for improving range of motion, flexibility, and preventing or managing back pain.
Back extensions are a great way to strengthen the back extensors and target the whole posterior chain. To perform a basic back extension, lie facedown on an exercise ball with your abdomen in the centre. Balance by pressing your feet into the floor behind you and, if needed, position your feet against a wall for support. Extend your arms overhead, in line with your ears, and bend at the waist, bringing your body down. Then, slowly raise your upper body and arms toward the sky until your shoulders are above hip height.
The bird-dog exercise also targets the back extensors. Start on your hands and knees with your shoulders over your hands and hips over your knees. Tense your abdominal muscles and stretch your right arm out in front of you. Hold this position while staying balanced. Then, slowly lift your left leg and extend it straight out behind you. Hold for 15 seconds and repeat on the opposite side.
Other exercises that strengthen the back extensors include the plank, bent-over rows, pull-ups, and lat pulldowns. The plank works the abdominals, arms, shoulders, hip flexors, and feet. For this exercise, lie on your stomach with your forearms on the floor and elbows in line with your shoulders. Tighten your abdominal and gluteal muscles, and lift your hips and knees off the floor. Hold for 10 to 30 seconds, focusing on maintaining a straight line from your knees to your shoulders.
Additionally, the lat pulldown is a staple exercise for building back strength. Stand with your arms extended, holding a resistance band taut and parallel to the floor in front of you. Keeping your arms straight, pull the band to your chest by moving your arms out to the sides. Initiate the movement from your mid-back, squeezing your shoulder blades together, and slowly return to the starting position.
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Trunk muscles protect vital organs
The trunk (torso) is the central part of the body that houses all the vital organs of the human body, except for the brain. The trunk muscles attach to the skeletal core of the trunk and are divided into two large groups based on their location.
The trunk muscles have several important functions, including contributing to the protection of the thoracic and abdominopelvic viscera. The muscles of the thoracic cage are the pectoralis major, pectoralis minor, serratus anterior, subclavius, intercostal, subcostal, and transversus thoracis muscles, including the diaphragm. These muscles support the thoracic cage and are involved in movements of the upper limbs and respiration.
The abdominal muscles are strong bands of muscles lining the walls of the abdomen. They are located towards the front of the body, between the ribs and the pelvis. The abdominal muscles include the rectus abdominis, pyramidalis, external obliques, internal obliques, and transversus abdominis. These muscles help to hold the internal organs in place, protect them, and provide core support. They also assist in maintaining posture and stability, and regulating internal pressure in the abdomen.
The rectus abdominis acts as a flexor of the trunk and an accessory muscle of expiration. It compresses the abdominal contents to protect them. The pyramidalis is a small triangular muscle found in the lower abdomen, which tenses the linea alba. The external obliques are a pair of muscles that allow the trunk to twist from side to side.
The diaphragm is a dome-shaped muscle that forms a partition between the thorax and the abdomen. It has openings for structures passing between the two cavities. The abdominal wall muscles consist of four muscle pairs arranged in layers, providing protection to the abdomen, which lacks bony reinforcements.
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Frequently asked questions
Trunk extensors are muscles that extend the vertebral column to maintain erect posture.
The erector spinae group of muscles are trunk extensors. They are a large muscle mass that extends from the sacrum to the skull.
Trunk extensors help maintain erect posture. They also play a role in protecting the thoracic and abdominopelvic viscera and assist with essential body activities such as breathing.
Back- and hip-extension exercises can help strengthen the trunk extensors. Examples include bridging, diagonal hip and shoulder extension, and trunk extension with fixed trunk or fixed legs.
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