PHYSIOLOGY OF THE SCAPULAR MUSCLE CHAINS

PHYSIOLOGY OF THE SCAPULAR MUSCLE CHAINS The muscular chains of the shoulder girdle can be dissociated depending on whether weconsider their points of support, their physiology, or their anatomical location. These threeparameters resulting from the evolutionary process specific to this belt, the study of theirphysiology in modern man is confronted with a juxtaposition of functions whoseeffectiveness largely responds to their adaptive capacity. This is why the classicphysiological functions of this belt will not be considered only from the abstract angle of theirmodern biomechanics, but as the instantaneous result of a succession of evolutionarystages. Three major functions can be individualized at the level of the shoulder girdle inhumans; traction (from brachiation), pressure and antero-posterior propulsion (related toquadrupedalism at rest and during movement), mobility (related to the abandonment ofbipedalism and secondarily to brachiation by release of the hand). The athlete only makes the best use of these different functions by seeking to favor the one that will allow him to be the most efficient in his discipline. The new constraints applied tothese structures are at the origin of all the pathologies encountered in this area. ➢ Traction This function, resulting from brachiation, is provided by two types of muscle groups workingin a chain, either direct (connection between the humerus and the thorax or the spine), orindirect (intermediate connection on the scapula and/or clavicle). ❉ Direct channels ● This system uses the muscles inserting directly on the thorax and the humerus by bypassing the shoulder joints. Three systems can be described: . The anterior chainconstituted by the pectoral major. . ● The intermediate chain through the deltoid . The posterior chain through the latissimus dorsi. These three muscles provide traction for the humerus towards thethorax. These are three powerful muscles, taking multiple supports on the thoraxand/or spine. ❉ Indirect channels These chains are made up of several muscle groups that use the scapula or clavicle as amechanical relay. These last two bones allow the initial force to be modulated or directeddifferently. The three areas of work already described for direct chains are identical to thoseused by indirect chains: . The anterior chain is made up of the small pectoralis whosefunction is to stabilize the scapula during traction by ensuring a fixed point on the thorax, thecoraco-brachialis, the short portion of the biceps and the subscapularis whose roles consistof ensuring the balance of the traction forces and bringing the the suspensory limb of thetrunk. . The upper chain includes the trapezius and deltoid to secure the scapula and the claviclewhen tensioning the supraspinatus muscles and the long portion of the biceps. . Theposterior chain is made up of the trapezius, the angular part of the scapula, the rhomboids

and the serratus major responsible for bracing the scapula to the trunk, and the "tractor"muscles themselves, that is to say the infraspinatus, teres minor and teres major muscles.These three muscle groups balance the forces exerted on the front and back parts of thetrunk and provide considerable traction force. The pathologies encountered at this level mayoriginate from an antero-posterior imbalance or an insufficiency of the stabilizing muscles(muscles of the upper chain). ➢ Displacement pressure ❉ Antigravity muscles The muscles which ensured the fight against gravity in our quadruped ancestors areessentially the stabilizers of the humeral head. The two main ones are the deltoid and thesupraspinatus for the anterior part, the infraspinatus and the latissimus dorsi for the posteriorpart. That is to say those “closing the humeral cuff upwards and backwards. ❉ Propulsion muscles They can be divided into two groups according to their physiology, the propellersstrictly speaking, that is to say the muscles whose contraction actively participates in themovement of the animal (internal rotators and retropulsion), and the "retractors'' whosefunction consists of to anteriorize the limb during the so-called suspension phase (externalrotators and antepulsion). The thrusters naturally constitute, because of their function, thegroup of the most powerful muscles (subscapularis, teres major, pectoralis major, latissimusdorsi), while the muscles responsible for bringing the limb forward are much weaker andfewer in number (sub- spiny, small round). This disparity is found at the level of the shouldergirdle of modern man, in which the external rotators are much weaker than the internalrotators. This inequality is at the origin of numerous pathologies in athletes who regularly usethe internal rotator/external rotator antagonism. ➢ Mobility Mobility is certainly the most modern characteristic of the human shoulder. It responds to thedefinitive liberation of the upper limb from locomotion. This function, independent of thenotion of force, integrates all of the shoulder muscles and the degrees of freedom of thethree joints ( degrees of freedom). Its acquisition responds much more to a mode ofintegration of information by the brain than to a structural modification of the shoulder girdle.The acquisition of gestural sequences, precision and spatial position of the upper limb havecertainly not restructured the fundamental elements of shoulder biomechanics during itsevolution. Pathologies linked to mobility may result from two very distinct etiologies,