Stability and control in the area of the core muscles are essential for maintaining a good posture with strength and efficiency. You can think of the core muscles as the chassis of a car – the supporting frame that keeps everything together in an organised and stable manner.
The trunk has three parts: the thorax, the abdomen, and the pelvis. The spine, ribcage, and sternum make up the thorax and they support the shoulders and the arms, while the pelvis, made of the sacrum and the ilium supports the hips and legs.
Between these two is the abdomen. It only receives structural support from the spine but must maintain its position in relation to the thorax and the pelvis. This is achieved through the action of several muscle groups.
The torso is wrapped around by what is known as an abdominal wall formed by the oblique and transverse abdominal (TVA) muscles together with rectus abdominis. This tube-like structure also receives support from its two open ends in order to be able to withstand high-impact activities or heavy compressions. The diaphragm provides this support at the top, while the strong pelvic floor muscles fulfil this role from the bottom. This whole muscular complex is wrapped in fascia in order to form an integrated whole.
The external obliques together with rectus abdominis form the outermost layer of the abdominal wall.
The internal obliques, which lie deep to the external ones, form the second layer. They originate at the thoracolumbar fascia, the iliac crest, and the lateral half of the inguinal ligament. The internal obliques insert into the cartilages of the lower 3–4 ribs, the xiphoid process of the sternum and linea alba. Bilaterally, they flex the vertebral column, depress the thorax and assist in respiration. Additionally, they also compress and support the lower abdominal viscera jointly with the transversus abdominis. Unilaterally, they rotate the thorax backward (together with the anterior fibres of the external oblique on the opposite side). The right internal oblique rotates the thorax clockwise, and the left one – counterclockwise, when the pelvis is fixed. Additionally, the lateral fibres (along with the lateral fibres of the external oblique on the same side) lat1erally flex the vertebral column approximating the thorax and pelvis.
The third, innermost layer is formed by transversus abdominis (TVA), which lies immediately beneath the internal obliques. It originates as fleshy fibres from the lateral third of the inguinal ligament, the inner surfaces of the cartilages of the lower 6 ribs, the thoracolumbar fascia, the inner lip of the iliac crest and partly integrates with the diaphragm. Anteriorly, it ends in a broad aponeurosis, inserting together with the internal obliques into the crest of the pubis and the pectineal line by forming the aponeurotic falx also known as the inguinal conjoint tendon. Superiorly, it also inserts into the xiphoid process of the sternum. It also passes horizontally to the middle line and inserts into linea alba. The upper ¾ sit behind rectus abdominis, while the lower ¼ is in front rectus abdominis.
The function of TVA is to compress the abdomen and provide lumbar stability by being preferentially recruited before any leg or arm movement is made. Thus, it compresses the viscera and provides both thoracic and pelvic stability as well. It also plays an essential part in helping pregnant women during delivery. The TVA, under normal conditions, works in tandem with the multifidi muscles at the back of the trunk along the spine.
In addition, to its essential role in core and back health, TVA also pulls the abdomen in to prevent a protruding belly. This is why its nickname is ‘the corset muscle’.
The pelvic floor
The pelvic floor, perineum, or pelvic diaphragm is an umbrella term for a number of muscles that extend from the sacrum and coccyx to the ischium and pubis. They support the organs of the pelvic cavity, flex the sacrum and coccyx, and also control the movement of material through the urethra, vagina (females), and the anus.
The pelvic floor makes a complete seal around the bottom of the torso. Statically, this sling supports the contents of the viscera above it. Much of the perineum’s stability is provided by thick layers of very strong fascia running across the upper and lower muscular surfaces.
Circular muscles called sphincters, guard the openings and provide voluntary control. Some superficial muscles compress the base and stiffen the penis in males to help with ejaculation and urination.
During pregnancy, these muscles and the fascia can get very stretched. A variety of pelvic floor exercises are recommended to maintain the musculature and prevent incontinence. Care needs to be exercised here. The muscles would usually recover after pregnancy from normal use. Some exercise may be beneficial but excessive strengthening can create hypertonicity and cause problems by compressing the bladder.
The importance of the core
It is important to develop and maintain a well-orchestrated functioning from all these muscles in order to effectively stabilise the trunk. When function is poor this can lead to a vast number of musculoskeletal dysfunctions.
These muscles need to be able to perform fine control activities regularly and often for extended periods of time. In most sports for example, the trunk needs to be maintained in a specific position relative to the body in a precise and continuous manner. The same applies to activities like yoga, gymnastics, or physical professions like – bodywork, hairdressing, etc. The good thing is that these activities also engage and develop the core muscles in a natural and continual manner. So, they are a better bet for long-term core health (if executed with proper posture and technique) than strength training type of exercises.
Sedentary lifestyles and jobs as well as prolonged sitting do not provide sufficient engagement for these muscles. Through under-stimulation these muscles lose their fine-control abilities and can become weak and inefficient.
If this situation degenerates it leads to trauma by causing non-core muscles to compensate for the dormancy of the core muscles. The non-core muscles can then become hypertonic and tight and contribute to pain and discomfort.
Research by Hodges and Richardson in 1996 investigated the relationship between low back pain and the activation of the core muscles. They discovered that in healthy individuals the transversus abdominus (TVA) would always be the first muscle to contract when during movements of the hip and arm. In people with low back pain, this pattern was reversed – superficial limb muscles contracted before TVA. This pattern of poor activation of this essential core muscle decreases the stability of the spine and increases sheer during leg and arm movements.
The practical significance of these findings led practitioners to focus on developing ‘lumbar stability’ in their clients with the aim of alleviating low back pain. Such programs usually feature various mobilising and strengthening routines that engage the core muscles from different angles. Established methods of improving core stability and function include Pilates, the Feldenkrais method, and the Alexander technique. Yoga and Tai Chi can also be an effective practice for developing a strong functional core although this is not their primary objective. Finally, various bilateral and unilateral bodyweight movements can also be an effective way of engaging and developing one’s core. One-legged squats, bodyweight deadlifts, and bridges do are excellent for this purpose.
Martin Stefanov Petkov