Dominic Stone
The trunk, or torso, is the central part of the body to which the head and limbs are attached. The trunk extensor muscles are those that hold the spine in an extended posture, counterbalancing the gravitational forces that act to pull the spine into flexion. Trunk extension exercises are important for building spine stability and improving muscle endurance to combat flexion stress. 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 and is responsible for extending the vertebral column to maintain erect posture. The trunk extensors also include the deep back muscles that occupy the space between the spinous and transverse processes of adjacent vertebrae. These muscles are important in maintaining posture, protecting the thoracic and abdominopelvic viscera, and assisting with essential body activities such as breathing, movement, defecation, and micturition.
| Characteristics | Values |
|---|---|
| Definition | Trunk extensor muscles hold the spine in an extended posture and counterbalance the gravitational forces that pull the spine into flexion. |
| Function | Extensor muscles contribute to the protection of the thoracic and abdominopelvic viscera and assist essential body activities such as breathing, movement, defecation and micturition. |
| Testing | Manual muscle testing is used to test trunk extension. Grades 1-4 are used to measure a patient's ability to raise the trunk to the horizontal level. |
| Exercises | Trunk extension exercises can improve endurance and combat flexion stress. |
| Strength | Studies show that men generally have higher trunk muscle strength than women. |
| Pain | Studies have shown that participants with lower back extensor strength are at an increased risk of experiencing a low back injury. |
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What You'll Learn
- Erector spinae muscles extend the vertebral column to maintain erect posture
- Intercostal muscles are located in spaces between the ribs and contract during forced expiration
- Rectus abdominis acts as a flexor of the trunk and an accessory muscle of expiration
- Trunk extension exercises are used to improve endurance and build spine stability
- Back extensor strength is associated with an increased risk of low back injury
Erector spinae muscles extend the vertebral column to maintain erect posture
The trunk of the body, or torso, houses all vital organs except for the brain. 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 posterior trunk, including the erector spinae, are responsible for vertically stabilizing the vertebral column.
The erector spinae is a large and superficial muscle that lies just deep to the thoracolumbar fascia. It is formed of three muscles: iliocostalis, longissimus, and spinalis. These muscles have fibres that run vertically throughout the lumbar, thoracic, and cervical regions. The erector spinae muscles are paired and segmental, allowing them to control movement at individual intervertebral junctions. This gives them fine control over the vertical stability of the vertebral column in both the sagittal and frontal planes.
The longissimus thoracis muscle is the largest of the erector spinae muscles. It is the longest muscle of the back, arising from the common origin of the erector spinae muscles and the transverse and accessory processes of the lumbar vertebrae. The longissimus thoracis muscle functions to hold the thoracic and lumbar regions erect.
The erector spinae muscles extend the vertebral column to maintain an erect posture. They serve as an important source of extension torque for antigravity activities, ranging from maintaining an upright posture to lifting objects from the floor. The muscles also control the forward flexion of the thorax.
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Intercostal muscles are located in spaces between the ribs and contract during forced expiration
The trunk, or torso, is the central part of the body to which the head and limbs are attached. The muscles of the trunk include those that move the vertebral column, form the thoracic and abdominal walls, and cover the pelvic outlet. The trunk muscles are divided into two large groups based on their location: anterior trunk muscles and posterior trunk 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 intercostals, internal intercostals, 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 intercostals are the most superficial intercostal muscles. They originate from the inferior border of one rib and insert into the superior border of the rib below. During inspiration, the external intercostals contract and elevate the ribs, increasing the transverse diameter of the thorax.
The internal and innermost intercostals aid in forced expiration by depressing the ribs. The deepest layer of the thorax wall is made up of the innermost intercostal muscles, which originate from the medial aspect of the costal groove of the rib above and insert into the internal aspect of the rib below.
The intercostal muscles work with other muscles of the thorax, such as the diaphragm, to facilitate respiration. The diaphragm is a dome-shaped muscle that forms a partition between the thorax and the abdomen. It is the main inspiratory muscle, contracting during inspiration to increase the vertical diameter of the thoracic cavity and producing lung expansion. During forced expiration, the internal and innermost intercostals contract to depress the ribs, aiding in exhalation.
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Rectus abdominis acts as a flexor of the trunk and an accessory muscle of expiration
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 and function. 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 rectus abdominis is a long, strap-like, paired muscle that passes vertically over the entire length of the abdomen. It is commonly referred to as the
As a flexor of the trunk, the rectus abdominis acts to flex the spinal column, drawing the pubic symphysis and sternum towards each other. It also tenses the anterior wall of the abdomen and assists in compressing the abdominal contents, protecting them. This compression increases intra-abdominal pressure, which is essential for basic bodily functions such as forced breathing, labour, defecation, and micturition.
The rectus abdominis also contributes to core stability, acting like a natural weight belt to protect the lower back from injury. Additionally, it stabilizes and controls the tilt of the pelvis (antilordosis).
The rectus abdominis can be isolated through exercises such as sit-ups, where the trunk is raised against gravity to the midline and then slowly lowered down in multiple sets.
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Trunk extension exercises are used to improve endurance and build spine stability
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 trunk muscles have several important functions, including contributing to the protection of the thoracic and abdominopelvic viscera and assisting essential body activities such as breathing, movement, defecation, and micturition.
The Trunk Extension Endurance Progression begins with the basic Trunk Extension on Ball Exercise. To perform this exercise, stand with your back against a wall or door, then lift your hips up and pull the ball under your hips. With the ball under your hips, the weight of your upper body is supported by your arms, which are on the ball or the floor. The Trunk Extension on Ball with Scapular Retraction exercise is a variation of this that adds an additional challenge by focusing on pulling the arms back by retracting the scapula. This moves the mass of the upper body further away from the ball, adding more work for the trunk extensors.
Another exercise for lumbar stabilization is the Biering-Sorensen test, which is used to assess muscle endurance around the lumbar region. This test can also be used to determine the immediate effects of Active Therapeutic Movement version 2 (ATM2), a device developed to improve pain and joint range of motion in patients with low back pain.
Trunk extension exercises can also be combined with other exercises to improve their effectiveness. For example, teaching a better stoop, deadlift, or squat can be helpful, but it is not a substitute for more focused trunk extension exercises. Additionally, lumbar stabilization exercise programs can include general exercises, educational and workplace-specific back school classes, psychological interventions, and segmental stabilization exercises.
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Back extensor strength is associated with an increased risk of low back injury
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 houses all the vital organs of the human body, except for the brain.
The trunk muscles have several important functions, including contributing to the protection of the thoracic and abdominopelvic viscera and assisting with essential body activities such as breathing, movement, defecation, and micturition. The erector spinae group of muscles, located on each side of the vertebral column, is responsible for extending the vertebral column to maintain erect posture.
However, it is important to note that specific strength training for the trunk muscles does not seem to be successfully integrated into athletic practice. Training recommendations for elite athletes typically focus on larger muscle groups that primarily impact athletic performance. Additionally, a recent systematic review found limited evidence that hip muscle performance is related to leg, ankle, and foot injuries. Instead, poor hip muscle performance might be a result of an injury rather than a contributing factor.
While trunk extensor strength is important, other factors also contribute to low back injuries. For example, impaired motor control of the trunk after sudden, unexpected perturbations has been linked to an increased risk of low back injury. Additionally, lumbar instability, inefficient lumbopelvic motor control, and impaired neuromuscular control of spine stability have been associated with low back pain.
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Frequently asked questions
Trunk extensor muscles are those that hold the spine in an extended posture, counterbalancing the gravitational forces that pull the spine into flexion. They are also involved in movements of the trunk, mainly flexion and rotation.
There are a few tests to measure the strength of your trunk extensor muscles. One example is the Biering-Sorensen test, which is a global measure of back extension endurance capacity.
Trunk extension exercises are great for strengthening your trunk extensor muscles. One example is the Trunk Extension on Ball exercise, which involves getting into a neutral spine position with your arms on an exercise ball or the floor, then performing an abdominal brace and lifting your arms.
