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Trunk rotation is a movement that involves the thoracic and lumbar vertebrae and surrounding muscles. The trunk muscles play a vital role in any motion the body performs, including walking and maintaining balance. They also help provide body stability. 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, for example, is responsible for extending the vertebral column to maintain erect posture. The abdominal oblique muscles, which include the external and internal oblique muscles, are also involved in trunk flexion and ipsilateral rotation. During ipsilateral rotation, the internal oblique and transversus abdominis muscles exhibit significantly increased activity compared to the 0-10% range of trunk rotation.
| Characteristics | Values |
|---|---|
| Muscles involved in trunk rotation | Latissimus dorsi, external oblique, internal oblique, transversus abdominis, rectus abdominis, lumbar multifidus |
| Muscle activity during ipsilateral trunk rotation | Increased activity in the internal oblique and transversus abdominis muscles compared to the 0-10% range of trunk rotation |
| Muscle activity during contralateral trunk rotation | Increased activity in the external oblique muscle compared to the 0-10% range of trunk rotation |
| Muscle activity during thoracic vertebral rotation | Significantly increased activity in the latissimus dorsi and external oblique muscles compared to the 0-10% range of trunk rotation |
| Role of LD muscle | Important for controlling upper trunk motions and shoulder extension |
| Role of IO and TrA muscles | Act early during ipsilateral trunk rotation at lumbar levels |
| Role of EO muscle | Percentage of MVC significantly increased during contralateral trunk rotation |
| Vertebral segments involved in trunk rotation | Thoracic and lumbar vertebrae |
| Benefits of trunk rotation exercises | Improved spinal mobility, flexibility, core strength, and sports performance |
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What You'll Learn
The role of the latissimus dorsi
The latissimus dorsi is a broad, flat, triangular muscle with extensive attachments to the spine, ribs, and pelvis, which converge onto the intertubercular groove of the humerus. It is one of the superficial (extrinsic) muscles that move the upper limb.
The latissimus dorsi is responsible for several functions, including extension, adduction, transverse extension or horizontal abduction, flexion from an extended position, and internal rotation of the shoulder joint. It also plays a role in the extension and lateral flexion of the lumbar spine. When the arms are in a fixed overhead position, the latissimus dorsi pulls the trunk upward and forward.
The muscle has been found to exhibit high activity levels during ipsilateral trunk rotation, with activation levels similar to those of the external oblique muscle. However, during contralateral trunk rotation, extension, and stability tasks, the latissimus dorsi displays low activity levels.
The latissimus dorsi is also associated with chronic shoulder and back pain. Tightness in this muscle can lead to sub-optimal glenohumeral joint (shoulder) function, resulting in chronic pain or tendinitis in the tendinous fasciae connecting to the thoracic and lumbar spine.
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The internal oblique and transversus abdominis muscles
Trunk rotation involves the movement of both the thoracic and lumbar vertebrae. During ipsilateral rotation at lumbar vertebral levels, the muscle activity of the internal oblique and transversus abdominis muscles is significantly increased.
The internal oblique muscles are a pair of muscles that lie on top of the external oblique muscles, just inside the hip bones. They are much thinner and smaller than the external oblique muscles. They work together with the external oblique muscles to allow the trunk to twist and turn. The internal oblique muscles originate from the anterior two-thirds of the iliac crest, the iliopectineal arch, and the thoracolumbar fascia. They insert onto the inferior borders of ribs 10-12, the linea alba, the junction with the cremaster muscle, and the pectineal line of the pubis (via conjoint tendon). The internal oblique muscles are innervated by the intercostal, subcostal (T7-T12), iliohypogastric (L1), and ilioinguinal nerves (L1).
The transversus abdominis is the deepest of the flat muscles, layered on top of the internal oblique muscles. These muscles help to stabilize the trunk and maintain internal abdominal pressure. The transversus abdominis has an extensive origin, arising from the costal cartilages of ribs 7-12, the thoracolumbar fascia, the anterior two-thirds of the iliac crest, and the iliopectineal arch. It crosses the abdomen horizontally to insert onto the linea alba, the aponeurosis of the internal abdominal oblique muscle, the pubic crest, and the pectineal line of the pubis. The muscle is innervated by the intercostal (T7-T11), subcostal (T12), iliohypogastric (L1), and ilioinguinal nerves (L1).
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The rectus abdominis muscle
Isolating the rectus abdominis muscle can be achieved by performing exercises with bent knees to minimise the engagement of hip flexors. For example, the sit-up exercise requires raising the trunk against gravity to the midline and slowly lowering it down repeatedly in multiple sets.
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The importance of vertebral segments
The vertebral column, or spine, is made up of 33 vertebrae, which are stacked on top of one another to form a protective canal for the spinal cord. These vertebrae are divided into five regions: cervical, thoracic, lumbar, sacral, and coccygeal. Trunk rotation involves both the thoracic and lumbar vertebrae.
Vertebral segments also play a role in maintaining spinal stability. In a study on the effect of body position on vertebral rotation, it was found that rotation was least in a "quadruped-like" position and increased in upright and supine positions. This suggests that the orientation of the spine in space influences the magnitude of vertebral rotation.
Furthermore, the spinal segments and their associated muscles contribute to trunk rotation. During ipsilateral rotation at thoracic vertebral levels, the activity of the latissimus dorsi and external oblique muscles increases significantly. Meanwhile, during early ipsilateral rotation at lumbar vertebral levels, the internal oblique and transversus abdominis muscles show increased activity.
The understanding of vertebral segments and their role in trunk rotation has implications for injury prevention and rehabilitation. For instance, trunk rotation is a key risk factor for low back pain, and by considering the specific vertebral segments involved, targeted exercises and treatments can be developed to address this issue.
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Trunk rotation exercises
Standing Trunk Rotation
To perform a standing trunk rotation, stand with your feet hip-width apart and facing forward. You can hold a medicine ball up by your chest, pressing it between your two palms with your elbows pointing out to the sides. Tighten your core muscles to stiffen your torso and pull your shoulders down and back, ensuring your lower back is not arched. As you exhale, slowly rotate your torso to one side, keeping your upper arms at your sides, elbows bent, and hands positioned at the midline of your body. Your head, chest, and torso should move together, and it is important to avoid leaning your torso in the direction of your rotation. Hold this position briefly before rotating to the opposite side. To increase the intensity of the exercise, you can fully extend your arms to shoulder height and maintain this position throughout the exercise, creating a longer lever that increases the load on your spine and challenges your core muscles.
Seated Trunk Rotation
For a seated trunk rotation, sit on the floor or a mat with your feet together, knees bent, and heels pressed into the floor. Holding a medicine ball close to your body, keep your spine straight and your torso perpendicular to the floor. Brace your core muscles and exhale as you slowly rotate your torso to one side. Ensure you do not lean backward, and keep the ball near the middle of your torso. Pause to inhale at the end of your rotation before moving to the opposite side.
It is recommended to perform eight to twelve repetitions of this exercise for three sets, with brief rests between each set.
Muscles Involved in Trunk Rotation
Trunk rotation involves the coordination of various muscles, including the latissimus dorsi, external oblique, internal oblique, rectus abdominis, lumbar multifidus, and transversus abdominis. These muscles work together to facilitate trunk rotation and maintain spinal stability.
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Frequently asked questions
The abdominal oblique muscles are active during trunk rotation, with the ipsilateral external oblique (EO) recruited during rotation to the right and the lower and middle regions of the contralateral internal oblique (IO) active during rotation to the left. The rectus abdominis, lumbar multifidus (MF), and latissimus dorsi (LD) muscles are also involved in trunk rotation.
Trunk rotation exercises are beneficial for improving spinal mobility, flexibility, and core strength. They can also help with body awareness and muscle control during movement, enhancing overall fitness and sports performance. Additionally, trunk rotation exercises are useful for reducing low back pain, a common issue among athletes and non-athletes.
Trunk rotation exercises can be performed in various ways depending on your fitness level and comfort. Start by practicing core engagement by tightening your abdominal muscles without moving your legs. Once you have control over your core, you can progress to moving your legs during the exercise. For a more advanced modification, try the supine position with legs extended, slowly bringing the outer knee toward the opposite side while keeping the other leg flat on the floor. Always focus on slow and controlled movements to effectively execute the exercise and reduce the risk of injury.
