ARTICLE understanding of these systems creates possibilities for relationships between structures that the older mechanistic views would often not acknowledge . 3
One muscular system within our human form that benefits from this change in attitude is the psoas system . Largely regarded as a flexor , stabiliser and postural muscle , the psoas is often misunderstood with regard to the depth of influence it actually wields on our form and function . 4
Due to its location within the deep core of our torso , the psoas lies in close proximity to significant bone and muscle structures , fascial sheaths , nerve pathways , lymphatic pathways , blood vessels , viscera and dynamic fascial movement lines . Due to nerve pathways and information substances within our tissues and fluids ( such as the neuropeptides ), the psoas is also responsive to autonomic stimuli such as sympathetic activation . 4 All of these relationships create a far greater complexity than its mechanistically described role as flexor and stabiliser suggests . It is thought that when the psoas system exerts tenacious restriction , it has a substantial impact on the functionality of the lower back , the mobility of the pelvis and hips , and the function of our digestive , urinary and reproductive organs .
The psoas system comprises three bilateral muscles : the psoas major , psoas minor ( in some individuals no longer present ) and iliacus muscles . These muscles have an interwoven relationship with other muscle groups as synergists and antagonists , including the respiratory diaphragm , trapezius , transverse abdominus , quadratus lumborum , hamstrings , and the diaphragmatic structures of our pelvic floor . The psoas system comprises the only muscular system that directly links our spine with our lower limbs .
The psoas major is a composite or hybrid muscle ( comprising type I , type IIa and type IIx slow and fast twitch fibres ) and is poly-articulate , crossing more than one joint - the lumbar , sacroiliac and iliofemoral joints . 5 Certain fibres of the muscle structure are involved with flexion , while others contribute significantly to the stabilisation of our midline . The psoas system thus forms an extremely important bridge between the lower thoracic vertebrae , the lumbar vertebrae , the pelvis and the femur bilaterally , potentially affecting all of them and their relationship of alignment and structural support .
These aspects of psoas influence are well known by body workers . However , many therapists still use deep tissue probing to reach the anterior aspects of the psoas fibres . This approach may be limited in its usefulness , potentially causing damage to the delicate adjacent structures with which the psoas is intertwined , and exacerbating restriction within its fibres by activating the fight and flight reflex in the muscle tissue itself . 4
No muscle in the human body operates in isolation . This most certainly applies to the psoas . However , due to its location deep in the core structure of the body , the psoas not only operates in conjunction with other muscle groups , but has an inextricable relationship with organs , blood vessels , nerve pathways and fascial sheaths , defined by dynamic movement lines such as the deep front line and superficial backline identified by Thomas Myers . 6 It therefore influences movement flow throughout the entire body .
The psoas system emerges embryologically where multiple rhythms of our metabolism express themselves : heartbeat , breath , swallowing , autonomic undulations , digestion . This means that psoas constriction may not only affect our musculoskeletal system but also our organ function , potentially contributing to impaired food absorption , chronic constipation and dysmenorrhea , and sexual dysfunction . 4
Understanding the psoas system in its entirety - and so being able to expand the spectrum of treatment approaches to psoas dysfunction - necessitates the investigation of one of the most fascinating features of the psoas system : its relationship with the nervous system .
On the one hand , it is wired into the conscious decision-making realm of our voluntary nervous system and is affected by , and in turn affects , significant nerve pathways , both directly and indirectly . It therefore provides essential sensory feedback to the CNS , contributing to proprioceptive feedback loops . 7
The psoas system is interrelated with the nerve pathways of the lumbar and sacral plexus and travels directly past the sciatic notch , where the sciatic nerve can become impinged . Conversely , psoas fibres are also directly affected by our ANS and respond particularly to sympathetic charge , which in a way gives the psoas a visceral quality . 8
The sympathetic division of the ANS is prominent in the thoracolumbar segments of the spinal cord at approximately T1 to L4 bilaterally , meeting the psoas at T12 and continuing all the way to L4 . Here , the preganglionic pathways of the sympathetic branch emerge from the spinal cord to form the ganglionic sympathetic trunk , which ultimately feeds into significant neural centres such as the adrenal glands and prevertebral coeliac and mesenteric ganglia . Deeply located fascial sheaths create an intimate relationship between these pathways of the nervous system and the fibres of the psoas . 9
When the sympathetic nervous system is activated by the neural and hormonal dynamics of the hypothalamic-pituitaryadrenal ( HPA ) axis , that activation has a direct impact on the integrity of the psoas fibres . The HPA axis is also known as our stress axis : the hypothalamus , located within the centre of the brain , relays neural stimuli to the pituitary gland . This causes a release
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