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Defining core strength

Hadyn Luke posted this on Friday 22nd of March 2013 Hadyn Luke 22/03/2013

Tags: Anatomy and physiology

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Defining core strength

In our blog today we are looking at core or trunk strength.

Many people perceive core strength to refer to the rectus abdominis and the abs, whereas the core is in fact the axial skeleton, which includes the neck, shoulder girdle, spine, hip girdle and pelvis. 

As any personal trainer will know, good core strength is therefore not only about having strong muscles in the rectus abdominis, it’s also about developing strength in the shoulder muscles, in the pelvic girdle and in the muscles that connect from the appendicular skeleton on to the axial skeleton. 

Joanne Elphinston and Paul Pook, authors of The Core Workout, state that: 

“Core stability is the ability of your trunk to support the effort and forces from your arms and legs, so that muscles and joints can perform in the safest, strongest and most effective positions.” 

The core can be broken down into an inner unit, a middle unit and an outer unit and it’s useful for a fitness instructor to understand how each of these work in supporting core strength.

Inner unit – this consists of minute control muscles in the inner layers, which connect from vertebrae to vertebrae. This includes the interspinales muscles, which connect from each spinous process to other spinous processes and are involved in the extension of the spine. There are also the rotatores, which are attached to the transverse processes (lateral vertebrae) and are involved in the rotation of the vertebrae. As they connect on the back of the spinous processes, they are also involved in the extension of the spine. Finally, the intertransverse muscles connect from one transvers process to another and are involved in lateral flexion of the vertebrae. 

Middle muscles – at the front is the transversus abdominis (TVA) muscle, which gives support from the anterior aspect of the trunk. On the opposite side is the multifidus, a deep muscle underneath the erector spinae, which is involved in the extension of the spine. At the top is the diaphragm, and giving support at the lower part of the core are the pelvic floor muscles. Supporting the side of the trunk are the lateral obliques. Surrounding these middle units is the Thoraco Lumbar Fascia (TLF), which holds in and compresses the core structure.

Outer muscle layer – these are the muscles that cause movement, such as the rectus abdominis, which causes flexion, and the erector spinae, which is more superficial than the multifidus. There are also the external obliques and the larger muscles that attach on to the appendicular skeleton, such as the latissimus dorsi, gluteus maximus, abductors, hamstrings, hip flexors and pectoralis major.

In an article published in the American College of Sports Medicine (ACSM) journal (February 2002) entitled: “EMG activity normalization for trunk muscles in subjects with and without back pain”, the authors stated that during the following movements, these muscles were important to core strength:

“Rectus abdominis demonstrated maximal activity in trunk flexion, external oblique in lateral flexion, internal oblique in axial rotation, and multifidus in extension.” 

In particular, they found that the latissimus dorsi is of major significance as it’s involved in several movements at once, including lateral flexion and rotation of the spine. It can therefore have a profound effect on core strength and posture because it’s involved in maximal activity in more than one plane. 

A recent study has also found that there’s evidence that higher muscle activity can be produced in combined exertions such as lateral flexion and rotation together, which shows the importance of ensuring that the latissimus dorsi is both strong enough and has sufficient flexibility to carry out these movements.

(see previous blogs on latissimus dorsi and hip flexors) 

Exercising core muscles

As the inner unit comprises deep muscle, the best way for a personal trainer to teach a client how to exert control over it is for them to ensure that the client has correct spinal alignment and is keeping a neutral pelvic tilt.

If a fitness instructor is asking a client to recruit their middle core, they need to create a ring of tension around the lumbar portion of the vertebrae, so when they contract these muscles, this will create an increase in intra-abdominal pressure, which gives the lumbar part of the vertebrae added stability.

When setting exercises for a client’s outer muscle layer, a personal trainer should encourage their client to work on the whole range of muscles in the area. If one particular muscle is overactive, that can lead to a change in posture that can affect trunk flexibility and core strength.

In addition, it’s important for a fitness professional to work a client’s thorasic region and keep this part of the spine extended by exercising the extensors in the upper back: the traps, rhomboids and rear deltoids. 

 

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