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The torso, or trunk, is the central part of the body to which the head and limbs are attached. The torso muscles are divided into two large groups, depending on their location. Trunk muscles contribute to the protection of the thoracic and abdominopelvic viscera and assist with essential body activities such as breathing, movement, defecation, and micturition. Trunk rotation exercises are popular for improving strength, function, and mobility in the trunk muscles. These exercises can be performed in a variety of ways, including standing, seated, and supine positions, and can also be done using a rotary torso machine. The primary muscles involved in torso rotation are the obliques, which are responsible for spinal rotation, but other muscles such as the quadratus lumborum, rectus abdominis, and transverse abdominis also engage to assist the core and stabilize the torso.
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What You'll Learn
Obliques are the primary movers
The torso, or trunk, is the central part of the body to which the head and limbs are attached. The trunk muscles are often the first ones activated when we twist and turn, helping to maintain stability.
The obliques are the primary movers of the torso. They are responsible for spinal rotation, or turning your torso to the side. The rotary torso machine, or torso rotation machine, is designed to strengthen the obliques. This exercise machine allows you to rotate your trunk against resistance, targeting your side abs, or obliques.
To isolate the obliques, you must rotate at the lumbar spine, not at the hips. While the torso rotation movement targets the obliques, several other muscles, including the quadratus lumborum, rectus abdominis, and transverse abdominis, engage to assist your core and stabilize your torso.
To perform a trunk rotation exercise, you can start by lying on your back on an exercise mat. Keep your knees bent and feet flat on the floor. Outstretch your arms and press them into the floor to help with balance during the movement. Engage your abdominal muscles and rotate your knees slowly to one side, working within your range of motion. Your feet will shift but remain on the floor. Hold the position for a few seconds, then engage your abdominal muscles again to move your legs to the opposite side.
You can also perform a standing trunk rotation by standing with your feet hip-width apart and facing forward. Hold a medicine ball up by your chest, pressing it between your palms with your elbows pointing out to each side. Tighten your core muscles to stiffen your torso and pull your shoulders down and backward. As you exhale, slowly start to rotate your upper body to the left. Keep your head, chest, and torso in one vertical line as you move. Don't bend your body in the direction of your movement. Hold the rotation momentarily, then slowly rotate to the right. Repeat the motion on both sides.
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Intercostal muscles between the ribs
The intercostal muscles are the muscles that link the ribs together and contribute to the process of breathing. They are located in the intercostal spaces between the ribs, with each muscle attaching to two ribs, one above and one below. There are 11 intercostal spaces in total, spanning the gaps between the 12 ribs.
The intercostal muscles consist of three layers: the external, internal, and innermost intercostals. The external intercostal muscles are the outermost layer, lying directly under the skin. They originate from the inferior border of the ribs and extend in an inferomedial direction to the superior border of the rib below. The external intercostals are responsible for expanding the chest wall during inhalation, pulling the rib cage together to create suction and pull air into the lungs.
The internal intercostal muscles form the intermediate layer, originating from the costal groove near the inferior border of the rib above and extending to the superior border of the rib below. They work in conjunction with the external intercostals during exhalation, helping to collapse the lungs and push air out of the lungs.
The innermost intercostal muscles cross more than one intercostal space and assist the internal and external intercostals in their function. They originate from the costal groove of the ribs and insert onto the superior border of the rib below.
Intercostal muscle strains or injuries can occur when these muscles are weakened, overexerted, or subjected to direct trauma such as falling or contact sports. Symptoms of intercostal muscle strain include sharp pain, stiffness, and mobility difficulties, often localized to the chest and trunk area. Treatment options include rest, cold and heat therapy, and OTC pain medications, with most strains healing within a 6-week timeframe.
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Serratus anterior rotates the scapula
The torso, or trunk, is the central part of the body to which the head and limbs are attached. The trunk muscles are responsible for assisting in essential body activities such as breathing, movement, defecation, and micturition.
One of the muscles that rotate the torso is the serratus anterior. This muscle is a fan-shaped muscle that originates from the upper eight or nine ribs and inserts along the entire length of the anterior aspect of the medial border of the scapula. It is innervated by the long thoracic nerve, a branch of the brachial plexus.
The serratus anterior is responsible for attaching the scapula to the thoracic wall and rotating the scapula by pulling its inferior angle laterally. This muscle is also involved in scapular protraction and scapular upward rotation, which is essential for anteversion of the arm. It acts in concert with the upper and lower fibres of the trapezius muscle to enable overhead lifting.
The serratus anterior is also known as the "boxer's muscle" as it is responsible for the protraction of the scapula that occurs when throwing a punch. It is a key scapular stabiliser, keeping the shoulder blades against the rib cage at rest and during movement.
Weakness of the serratus anterior can lead to scapular winging and impaired scapular protraction and upward rotation, reducing overall scapular and shoulder stability, and increasing the risk of injury.
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Rectus abdominis is the main ab muscle
The rectus abdominis is a long muscle in the abdominal wall. It extends from the rib cage to the pubic bone and is divided into two segments by the muscle called the linea alba. The rectus abdominis is one of the five main abdominal muscles, along with the pyramidalis, external obliques, internal obliques, and transversus abdominis. Together, these muscles act like a natural weight belt, protecting the lower back from injury and stabilising the torso.
The rectus abdominis is often referred to as the "abs muscle" and is responsible for holding internal organs in place, such as the stomach, intestines, pancreas, liver, and gallbladder. It also keeps the body stable during movement, providing core support and assisting in essential bodily functions like breathing, coughing, vomiting, and childbirth. In individuals with low body fat, the rectus abdominis may be visible as a "six-pack".
The rectus abdominis muscle is paired and runs vertically on either side of the linea alba. It is attached by two tendons: a larger one connected to the pubic crest and a smaller, medial tendon attached to the pubic symphysis. The most superior intersection is generally at the level of the xiphoid, while the lower intersection is at the level of the umbilicus.
To strengthen the rectus abdominis, exercises such as sit-ups and trunk rotations are effective. During trunk rotations, the abdominal muscles are tightened, and the knees are slowly rotated to one side, working within the individual's range of motion. This exercise improves the strength, function, and mobility of the trunk muscles, including the rectus abdominis, and can be beneficial for reducing lower back pain.
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Trunk rotation exercises
Standing Trunk Rotation
This exercise can be performed with or without a medicine ball.
- Stand with your feet hip-width apart and facing forward. If using a medicine ball, hold it up to your chest, pressing it between your palms with your elbows pointing out.
- Tighten your core muscles to stiffen your torso and pull your shoulders down and back. Do not arch your lower back.
- Exhale and slowly rotate your torso to one side, keeping your head, chest, and torso aligned.
- Hold the end position briefly before rotating back to the centre and then repeating on the other side.
Seated Trunk Rotation
This exercise can also be performed with a medicine ball.
- Sit on the floor or a mat with your feet together, knees bent, and heels pressed into the floor.
- Hold the medicine ball close to your body, keeping your torso perpendicular to the floor.
- Exhale and slowly rotate your torso to one side, keeping your spine straight and avoiding leaning backward.
- Pause and inhale at the end of the rotation, then rotate back to the centre and repeat on the other side.
Trunk Rotation on an Exercise Mat
- Lie on your back on an exercise mat with your knees bent and feet flat on the floor.
- Maintain your shoulders and upper body firmly against the floor and outstretch your arms, pressing them into the floor for balance.
- Engage your abdominal muscles and slowly rotate your knees to one side, working within your range of motion.
- Hold the position for 3-5 seconds, then engage your abdominal muscles again to rotate your legs to the opposite side.
Progressing the Exercise
To increase the intensity of trunk rotation exercises, you can perform them with your feet raised off the floor and knees bent at a 90-degree angle. You can also try extending your legs to further engage the core muscles.
Additionally, for standing and seated trunk rotations, you can fully extend your arms to shoulder height during the exercise, creating a longer lever that increases the loading on the spine and requires more effort from the core muscles.
Remember to work within your fitness level and always maintain control during the exercise.
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Frequently asked questions
The trunk muscles are targeted when rotating the torso. The obliques are the primary movers, responsible for spinal rotation.
Torso rotation exercises improve strength, function, and mobility in the trunk muscles. They can also help with low back pain and increase lumbar spine and hip flexibility.
There are various torso rotation exercises, including standing trunk rotations, seated trunk rotations, and exercises using a rotary torso machine.
