Abstract
Corresponding Author(s)
John J. Dougherty, DO, FACOFP, FAOASM, Chair–Family Medicine, Kansas City University of Med and Bio Sciences, 1750 Independence Ave., Kansas City, MO 64106-1453.
E-mail address: JDougherty@kcumb.edu.
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Core training has found its way into the lexicon of countless exercise regimens. However, clinically there has been little comprehensive definition and even less practical characterization of this “core.” The word core derives from the Greek word kormos, which loosely translates to “trunk of a tree.” An additional word origin comes from the Span- ish word for heart, corazon. George Lucas selected “Cora- zon” as the name for the planet at the center of his “Star Wars” universe. All of these expressions allude to the center of a structure. The core is in essence exactly that, the central portion of the body, and is composed of the torso, pelvic and shoulder girdles and their musculature, connective tissues, and osseous structures.1-5 functional unit, synergistically adjusting the entire body to maintain balance, postural stabilization, and mobility. These abilities are essential in the performance of basic activities of daily living (ADLs).7
Neurologic and musculoskeletal impairments can alterthese normal biomechanical relationships.8-10Such impair-ment effects a functional shift of the structural burden to thecomponents of the core.1The resultant alterations imposespecific distinctive demands, resulting in applied adapta-tions that often lead to somatic dysfunction.8-10These dys-functions manifest in both the osseous framework and theirsupportive muscle groups.7-10Defining these distinct inertand active core components is the objective of this article.
Anatomy– overview
The core is composed of the torso, or trunk, and the pelvicand thoracic girdles.1,3-5Factors contributing to stabilityand function, and therefore the biomechanical integrity,include an osseous scaffolding, multiple dynamic musclegroups, cartilaginous and ligamentous structures, and a var-ied and diverse set of joints. The alignment of underlyingboney frame has a direct relationship to the effectiveness ofthe applied forces from the relative motor unit.5
The musculature of the core in turn aligns the spine, ribs,and pelvis, allowing for the absorption and dispersal ofexternally applied forces, whether static or dynamic, to acontrolled direction. Appropriate muscle recruitment andtiming is extremely important in providing stability.5,11These muscles consist of both local and global stabilizingsystems that must work coherently to achieve this disperse-ment. Alteration of the relationship between any of thesecomponents can result in proprioceptive imbalance, unduewear, and potential disruption of ligamentous or cartilagi-nous structures.6The core, as described, is composed ofinert and active structures. These distinct yet symbioticsubsets each have further divisions that are responsible fora particular function.The inert skeletal frame is what delineates the shape ofthe torso.4,10Defining the “normal” relationship of the in-terconnected bones is important when contemplating theirfunctional responsibilities. The base of the core lies withinthe pelvis and therefore the pelvic girdle, which is com-posed of the right and left innonimates, and is conjoinedposteriorly via syncytial joints to the sacrum.3Medial, an-terior, and inferior, the pubic symphysis joint functions as apoint of stabilization within this closed system. The pelvicgirdle is loaded via the lumbar-sacral joint transmittingweight from the axial spine. The thoracic spine lies stackedon the five lumbar vertebrae. The ribs arise from the tho-racic spine and frame the thoracic cage, anchoring anteriorlyto the sternum. The sternum articulates via a hyaline carti-laginous interface, completing the cage.
With the exception of the pubic symphysis (cartilag- enous articulation) and the first rib articulation to the ster- num (synchondrosis), all of the relevant joints of the core are plane or gliding joints. These gliding joints allow only a slight slipping or sliding of one bone over the other and are formed by the apposition of plane surfaces— one slightly concave and the other slightly convex. These joints articu- late between processes of the vertebrae, at the costovertebral and sternocostal juncture, and are enveloped by capsules lined by synovial membrane. The amount of motion be- tween the surfaces is limited by the ligaments or by the articulating bones.
Anchored upon this thoracic core are the scapulas, pro- viding a stable articulation for the upper extremities and allowing for effective locomotor function of the appended extremities. The scapular-thoracic articulating surfaces form what is termed a false joint. The components of this “articulation” are married in their form and function be- cause of the shared muscular support and not a true osseous interface.10
The connective tissues within the framework simultane- ously provide both stability and flexibility. Between any two adjacent vertebrae rests a tough but elastic fibrocarti- laginous intervertebral disk. These intervertebral cushions contribute to the stability of the spinal column because they are strongly bound to the vertebrae, yet allow for consider- able movement between the adjoining bones. Furthermore, they allow the spinal column to absorb significant weight-
bearing loads. A soft gelatinous center, the nucleus pulpo- sus, lends resilience to the joint.
Anterior and posterior to the spine lie the longitudinal ligaments. Ligaments are composed of collagenous fibers that are pliant and flexible. It is this elasticity of the ligament that in the correct biomechanical position can act as a contributor to or a substitute for muscle power. These lig- aments, along with the apposition of the boney articulation at their anatomic endpoint, limit movement.
Sensory-motor control
An established relationship has been demonstrated amongcore stability, balance performance, and activation charac-teristics of the trunk muscles.1Sensory-motor control is anintegral component because it relates to postural response,stability, mobility, and proprioception. All skills are bothinnate and yet trainable. The role of sensory-motor controlis much more important than the role of strength or endur-ance of the core musculature. For example, anxiety associ-ated with a position the individual has not experienced or isuncomfortable with results in a reactive response, placingthe body into a posture in which the muscles of record havecontrol of balance.6,12,13The central nervous system (CNS) then creates a stablefoundation for movement through co-contraction of partic-ular muscles. The contributions and sequence of the varioustrunk muscles involved in recovery depend on the taskbeing performed.6This “muscle memory” of the position, towhich balance confidence is reacquired, is a learned skillthat can be effected with repetition. This appropriate musclerecruitment and timing is an extremely important tenet inproviding core stability. 13
Functional responsibilities
Static function
A secondary, but equally important, static function is autonomic. The core muscles provide stabilization of the thorax and the pelvis during internal pressure necessary to
Primary function
Compress and support abdominal viscera, flex and rotate trunk
Compress and support abdominal viscera
Flexes trunk (lumbar vertebrae) and compresses abdominal viscera
Helps to support the pelvic viscera and resists increases of intra- abdominal pressure
Inspiration, braces abdominal viscera
Dynamic function
Insertion
Innervation
Linea alba, pubic tubercle, and anterior half of iliac crest
Inferior border of 10th-12th ribs, linea alba, and pectenpubis via conjoint tendon
Linea alba with aponeurosis of internal oblique, pubic crest, and pectin pubis via conjoint tendon
Xiphoid process and 5th-7th costal cartilage
Perineal body, coccyx, anococcygeal ligament, walls of prostate or vagina, rectum, and anal canal
Thoracoabdominal (inferior 6 thoracic nerves) and subcostal nerve
Thoracoabdominal (ventral rami of inferior 6 thoracic nerves) and first lumbar nerve
Thoracoabdominal (ventral rami of inferior 6 thoracic nerves)
Nerve to levator ani (branches of S4) and inferior anal (rectal) nerve and coccygeal plexus
Phrenic nerves (C3-C5), peripherally intercostal nerves (T5-Y11), and subcostal nerves (T12)
Sternal: Posterior xiphoid process
Costal: interior, inferior six costal cartilages and adjoining ribs on each side Lumbar: Medial and lateral aponeurotic arcuate ligaments, and anterior L1-L3)
Thoracolumbar fascia, anterior two-thirds of iliac crest, and lateral half of inguinal ligament
Internal surfaces of 7th-12th costal cartilages, thoracolumbar fascia, iliac crest, and lateral third of inguinal ligament
Pubic symphysis and pubic crest
Musculature
External surfaces of 5th-12th ribs
Body of pubis, tendinous arch of abturator fascia, and ischial spine
The musculature of the core can be divided into four distinct functional groups based on the movement that is produced. These groups are named based on the primary direction of movement when they are actively function- ing as stabilizers. The four groups are anterior, posterior, medial, and lateral.16-22
Table 1 Anterior Core Musculature
Muscle
Anterior Musculature External Oblique
Origin
Internal Oblique
Transverse abdominus
Rectus abdominis
Levator ani
Diaphragm
242
Table 2 Posterior Core Musculature
Muscle Origin Insertion Innervation Primary function Posterior musculature
Extrinsic back muscles
Latissimus dorsi Spinous processes of inferior 6 thoracic vertebrae, thoracolumbar fascia, iliac crest, and inferior 3 or 4 ribs
Intertransversii lumborum Transverse processes of lumbar
vertebrae
Intermediate Layer of intrinsic back muscles
Floor of intertubercular groove of the humerus
Transverse processes of adjacent vertebrae
Thoracodorsal nerve (C6, C7, and C8)
Dorsal and ventral rami of spinal nerves
Extends, adducts, and medially rotates the humerus: raises body toward arms during climbing
Osteopathic Family Physician, Vol 3, No 6, November/December 2011
Aid in the bending of vertebral column; acting bilaterally, they stabilize vertebral column
Erector spinae: Iliocostalis Lumborum Longissimus
Deep layer of intrinsic back muscles
Arises by a broad tendon from posterior part of iliac crest, posterior surface of sacrum, sacral and inferior spinous processes, and supraspinous ligament
Fibers run superiorly to angles of lower ribs and cervical transverse processes, fibers run superiorly to ribs between tubercles and angles to transverse processes in thoracic and cervical regions
Dorsal rami of spinal nerves
Acting bilaterally, they extend vertebral column and head; as back is flexed they control movement by gradually lengthening their fibers; acting unilaterally, they laterally bend vertebral column
Multifidus Arises from the sacrum and the ilium, transverse processes of T1-T3, and articular processes of C4-C7
Rotatores Arise from the transverse processes of vertebrae; are best developed in thoracic region
Minor deep layer of intrinsic back muscles
Interspinales lumborum Superior surfaces of spinous
processes of lumbar vertebrae
Fibers pass superomedially to spinous processes of vertebrae above, spanning 2-4 segments
Pass superomedially to attach to junction of lamina and transverse process of vertebrae above their origin, spanning
1-2 segments
Inferior surfaces of spinous processes of vertebrae superior to vertebrae of origin
Dorsal rami of spinal nerves
Dorsal rami of spinal nerves
Dorsal rami of spinal nerves
Stabilizes vertebrae during local movement of vertebral column
Stabilizes vertebrae and assist with local extension and rotary movements of vertebral column; may function as organs of proprioception
Aid in extension and rotation of vertebral column
Posterior abdominal wall
Quadratous lumborum Medial half of inferior border
of 12th rib and tips of lumbar transverse processes
Iliolumbar ligament and internal lip of iliac crest
Ventral branches of T12 and L1-L4 nerves
Extends and laterally flexes vertebral column; flexes 12th rib during inspiration
Table 3 Lateral Core Musculature
Muscle Origin Insertion Innervation Primary function Lateral musculature
Gluteus medius External ilium Lateral greater trochanter Superior gluteal
L5, S1
Abducts and medially rotates thigh, keeps pelvis level
Gluteus minimus External ilium Anterior greater trochanter
Superior gluteal L5, S1
when opposite leg is raised
Piriformis Anterior sacrum, sacrotuberous ligament
Superior gemelius Superior ischial spine,
Inferior Ischia tuberosity
Inferior gemelius Superior ischial spine,
inferior ischia tuberosity
Obturator internus Obturator membrane and
surrounding bones
Quadratus femoris Lateral border of ischial
tuberosity
Quadratus lumborum Medial half of inferior border
of 12th rib and tips of lumbar transverse processes
Superior aspect of greater trochanter
Medial aspect of greater trochanter
Medial aspect of greater trochanter
Medial aspect of greater trochanter
Quadrate tubercle of femur
Iliolumbar ligament and internal lip of iliac crest
Anterior branch S1-S2
N. to obturator L5, S1
N. to quadratus L5, S1
N. to obturator L5, S1
N. to quadratus L5, S1
Ventral
branches of T12 and L1- L4 nerves
Laterally rotate extended thigh and abduct flexed thigh, steady femoral head in acetabulum
Laterally rotates thigh, steadies femoral head in acetabulum
Extends and laterally flexes vertebral column, fixes 12th rib during inspiration
meanwhile are independent in unilateral movements and assist in trunk rotation and lateral flexion.20,22,24
rotation. The multifidus muscles provide stabilization by increasing intra-abdominal pressure and are particularly active in sagittal plane movements as mentioned before. With these muscles actively contracting during rotation, thus preventing trunk flexion, they also increase the spi- nal stiffness through their co-contraction with the trans- verse abdominus.26,31,32,36
The medial and lateral core muscles provide medial and lateral stability to the entire core/lumboplevic complex. These muscle groups provide the integral link to transfer of force and support from the distal to proximal segments of the entire kinetic link system and provide support for the spine. Anteriorly, the force is redirected in part because of the relationship of the transverse lateral fascia-abdominals and their connection to the gluteal musculature and pos- teriorly via the connection between the multifidus mus- cles as they blend into the superior medial aspect of gluteus maximus.
Table 4 Medial Core Musculature
Muscle
Medial musculature
Adductors brevis
Origin
Insertion
Innervation
Primary function
Adductors magnus
Body and inferior pubic ramus
Inferior pubic ramus, ischial ramus
Body and inferior pubic ramus
Pectineal line, proximal linea aspera
Gluteal tuberosity, linea aspera, medial supracondylar line
Middle 1/3 of Linea aspera
Obturator L2, L4
Adducts thigh
Obturator L2-L4
Adducts thigh and to some extent flexes
Adductors longus
Obturator L2-L4
Pectineus
Superior ramus of pubis
Pectineal line, just inferior to lesser trochanter
Femoral L2, L3
Iliopsoas: Psoas minor Psoas major
Sides of T12-L1 vertebrae Pectineal line, iliopectineal
eminence
Lesser trochanter of femur
Adducts thigh adductor part: flexes thigh Hamstring part: extends
thigh
Adducts and flexes thigh; assists with medial rotation of thigh
Acts conjointly in flexing thigh at hip joint and in stabilizing joint
Iliacus
Sides of the T12-L5 vertebrae
Iliac crest, iliac fossa, ala of sacrum, anterior sacroiliac ligaments
Lesser trochanter and femur distal to, tendon of psoas major
Ventral rami of lumbars L1, L2
Ventral rami of lumbars L1, L2, L3
Femoral L2, L3
Conclusions
A basic precept of osteopathic medicine is the interrelation- ship between structure and function. The connection of the structure and function of the core is a reflection of this truism. The structural components outlined in this discus- sion function to reduce force load, dynamically stabilize, and generate strength against abnormal forces. An effective core allows for the maintenance of an optimal relation- ship of the functional agonists, which makes it possible for the body to maintain favorable biomechanical rela- tionships. This biomechanical interconnectivity affects routine activities of daily living, which is, in essence, human performance.
The goal of this paper was to define the individual muscular contribution of core musculature. As research progresses, the definition may change with a few variations; however, the contribution of the muscles identified will assist by serving as a benchmark definition. By understand- ing the muscles contributing to core stability, it is hoped that the individual practitioner will take into consideration ana-
tomical core function and postural activation when evalu- ating their patients.
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