The Core Muscles – Functions, Facts and Exercises

The body’s core is essentially a more or less cylindrical, muscular box, that encloses the abdominal organs. It consists of 3-4 muscle layers, the innermost of which is sometimes referred to as the ‘deep core’.

The innermost deep core muscles: 
• transversus abdominis (TA) – the front, sides and side back 
• transversospinalis (principally multifidus) – the back (between the vertebrae) 
• respiratory diaphragm – the roof 
• pelvic floor – the floor 
• quadratus lumborum (QL) – the side back
(The quadratus lumborum is included here because of its importance in stabilising the floating rib attachments of the diaphragm)

When contracting as a team, all these deep core muscles compress the abdominal cavity and raise intra-abdominal pressure. It can be further squeezed by the more superficial muscle layers, enabling ‘things’ to be expelled downward (defaecation, childbirth) or upward (forced expiration, vomiting, coughing, sneezing etc.). 

The central anterior ‘seam’ where the left and right sides of the body join is the linea alba and the abdominal muscles attach to it via a thin tendinous, fascial membrane called the abdominal aponeurosis.
The posterior ‘seam’ is formed by the spine, with the muscles attached into the thoraco-lumbar fascia.
It might help to visualise the anterior linea alba as a sort of zip, holding 2 strong, inelastic, flexible pieces of ‘fabric’ together, from which the elastic muscular fibres wrap around the body. Posteriorly the muscle fibres again attach to similar firm pieces of ‘fabric’ which meet at the spine, where the multifidus muscles could be visually likened to the laces of the second corset. However, whereas the laces hold the 2 sides together, the multifidus group compress the spine vertically.

Hiccups are involuntary contractions of the diaphragm. Each contraction is followed by a sudden closure of the vocal cords, which produces the characteristic “hic” sound. They can be caused by a large meal, swallowing air while eating /drinking, alcoholic or carbonated beverages or sudden excitement. Occasionally, prolonged hiccups may be a sign of an underlying medical condition. Hiccups are only found in mammals, and are most common in infants, becoming rarer with age. This may suggest that they evolved to allow air trapped in the stomach of suckling infants to escape, allowing more milk to be ingested. (Remedies include distracting the person, concentrating on something like heart beats and big movements of the diaphragm – a very deep inhalation, continuing to suck in as much breath as one can, holding the breath, then as complete an exhalation as possible, continuing to squeeze out as much breath as one can and holding the breath out. Another possible cure could be the yoga breathing exercise kapalabhti).

The abdominal walls are reinforced by the crisscross effect of the internal and external abdominal obliques and the vertical stability is provided by the rectus abdominis and errector spinae group.

When all the muscles contract together, while attempting to exhale against a closed airway (either throat or nose), this creates a firm pressurised column and is known as the valsava maneuver. It is used by body builders when powerlifting and for some cardiac function tests. Because it alters the rhythm of the heart, it can help stop palpitations caused by anxiety. When the nose is pinched, instead of closing the throat, Pressure is also raised in the head and can be used to equalise pressure and shift blockages in the ears and sinuses.

In addition to providing a flexible and compressible container for the abdominal organs, the core muscles perform or assist the various movements of the torso: flexion-extension, side bending / lateral flexion and rotation.  

Muscles that attach the torso to the legs and operate the hip joints are sometimes included as part of the core, especially the psoas major and minor and even the iliacus. This is partly because of the psoas’ location down the inside back wall of the abdominal cavity (the iliacus the back wall of the pelvic cavity), that the spinal attachments of the psoas overlap with those of the diaphragm and the role of the psoas in lumbar extension / flexion which is not discussed here.
A stable core forms the anchor, from which the hip muscles are able to operate the hip joints and move the legs. Thus, using the iliopsoas to raise the legs against gravity demands more muscular work to maintain a stable core and can be part of a sequence of core strengthening exercises.

CORE STRENGTHENING SEQUENCE

Youtube video of this sequence

1. Support head and neck in clasped hands to allow the throat area to remain relaxed and open. Curl up to engage the abdominal flexors and keep the lumbar spine fixed.
Alternately extend each leg up on inhale and slowly exhale to lower it towards the floor, eccentrically contracting the iliopsoas. Then bend it into the chest, in a bicycling movement 3-5x. Rest if needed. Repeat with a slight twist of the upper body to one side then the other to focus more into the oblique muscles 3-5x.
2. Twist the upper body to one side and both knees to the other and hold for 3-5 breaths with minimal effort.

Pause here, supine with knees bent, hands on belly and take a few relaxed abdominal breaths, softening and relaxing all the muscles which have just been working.

3. Roll onto one side; knees bent up level with pelvis, head resting on underneath arm. Wrap uppermost arm over head to support from the opposite side. Exhale to lift head and chest up off the floor, while also lifting uppermost shin and foot (internally rotating the hip) contracting the side waist (abdominal obliques and QL). Inhale lower to floor and arch the underneath side of the waist off the floor. Repeat 3-5x (+/- hold 3-5 breaths).
4. Lie prone with forehead on the floor arms forward alongside head (or 90º to sides with elbows bent to 90º). Press pubis into the floor, exhale to lift head, one arm and diagonally opposite leg, inhale down. Repeat opposite diagonal 3-5x (+/- hold 3-5 breaths)
5. Place hands under shoulders, ‘glue’ hands to the mat, lift the torso and let the pelvis hang back behind the knees to create some traction in the torso and spine. 1-2 breaths.
6. Relax in child’s pose, breathing into the back ~5 breaths.

See a video of this sequence on Youtube

ABDOMINAL – PELVIC FLOOR – LOW BACK STABILISING LOCK
MULA BANDHA?

This co-contraction of a triad of muscles, lower transversus abdominis, transverse perineal muscles and multifidi, stabilises the low back and sacroiliac joints and is especially in yoga therapy useful when there is an injury, pain or hyper-mobility.
It seems very likely that this is what is meant by Mula Bandha.

Lying supine with knees bent. Exhale fully and gently engage the lower TA, below the navel, as if squeezing it in and slightly downwards, towards the pelvic floor. Eventually you’ll notice a subtle lift of the pelvic floor.
Inhale release. Repeat several times, allowing the area to soften and expand on the inhale.
Engage the lock and hold with a few normal breaths.
Engage the lock and do a few twists, taking the knees from side to side, breathing as normal.
Practice engaging the lock while doing other small simple movements, then when walking.
The muscular contraction should more like subtle tone rather than tension or effort.
Be sure to completely relax when the lock is not required, breathe into the area and feel the expansion of the muscles.
More specific pelvic floor exercises will be in another post.

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