The muscles of the trunk & the core – what are their functions & how do you strengthen them

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Written by Clean Health Online Master Coach, Kimberly Leggett

Trunk muscles are those which form the central part of the human body which extend the neck and limbs, including the thorax and abdomen.

Pectoral Muscles lie in the chest and exert force through the shoulder to move the upper arm. The serratus anterior is one such muscle. 

Serratus anterior – the word serratus comes from the word “saw” and anterior meaning “front” which is a major proctactor of the scapula. These muscles are involved in pushing, punching and throwing movements as it allows for elevation of the upper arm.

This can be strengthened by exercises such as the serratus anterior raise which acts as a great little accessory exercise for the bench press.Internal obliques – the word internal meaning “towards the inside” and oblique meaning “running at an angle”.

The internal obliques can work bilaterally to create flexion of the trunk, compression of the abdominal viscera, expiration and an increase of intra-abdominal pressure.

They can also work unilaterally to create ipsilateral trunk lateral flexion and ipsilateral trunk rotation.External obliques – the word external means “outside” and oblique means “running at an angle’ with their proximal attachments on the external surfaces of ribs 5-12.

The external obliques can work bilaterally to create flexion of the trunk, compression of the abdominal viscera, expiration and an increase in abdominal pressure. They can also work unilaterally to create ipsilateral trunk lateral flexion, and contralateral trunk rotation. Exercises such as a side plank, standing trunk rotation, Russian twists, and Copenhagen planks can help strengthen the obliques

Rectus abdominis- the word rectus means “straight” and abdom refers to the abdomen aka – those sit up/visible 6 pack abs that all the boys want and all the girls love to see!

The function of these muscles include flexing and rotting the trunk, fixes and depresses the ribs, stabilises the pelvis and increases intra-abdominal pressure. Popular ways to develop these muscles include sit-ups and crunches which are trunk flexion exercises. That being said, performing compound movements with heavy loads will also use these muscles and are an indirect way of working them.

Transversus abdominis – Transverse means to run horizontally and their function is to compress abdominal contents which aids in spinal stability. Planks and bracing are some of the most effective ways to strengthen these muscles.Multifidis – A group of muscles that belong to the transversospinal group of deep back muscles, alongside rotatores and semispinalis.

The multifidus is regionally divided into the multifidus cervicis, thoracis, and lumborum.The muscles of the multifidus work bilaterally to extend the spine; and unilaterally to laterally flex the spine ipsilaterally, and to rotate the spine contralaterally.The multifidus is not considered a prime mover for spinal extension, but is important for segmental stability of the spine. The bird dog is one great exercise to strengthen these muscles.Erector spine –Erector comes from the word “erect” and spinae refers to the spine.

This is made up of 3 muscles, the iliocostalis, longissimus and spinalis. Each attaching at various points of the spine, ribs, skull, and hip bones. These muscles all work synergistically to extend the vertebral column. Compound exercises such as squats and deadlifts are a great way to train them as they contract the muscles isometrically to resist spinal flexion. Quadratus lumborum- quad refers to “four-sided” and lumborum refers to the lumbar region.

When they are activated unilaterally, they will laterally flex the vertebral column, whilst bilaterally they will extend the lumbar spine. These muscles are also involved in fixing the 12th rib during forced inspiration and help maintain upright posture. Side Planks and unilateral farmers carry are great QL strengtheners.Lumen Candela. (2020). Trunk Muscles. Boundless Anatomy and Physiology.

Retrieved from: Oreb, Sebastian. (2020). Muscles of the trunk and core. Strength Systems International Certification Level 2. Clean Health Fitness Institute. 

To not only make the first step & turn your passion for fitness into a sustainable career but to also up-skill & enhance your knowledge around nutrition & training, click here to learn more about our Strength System International Certification Level 1 & 2 Authored By Sebastian Oreb! 

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