FMA elbow function and muscle recruitment notes PDF

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UPPPER LIMB FUNCTION – A KINETIC CHAIN • The shoulder girdle positions the upper arm; • The elbow adjusts the arm length; • The forearm rotates the hand; • The wrist allows fine tuning of the hand position to occur; • The fingers act to manipulate or grasp the object. FUNCTION OF ELBOW REGION MUSCLES • Mover (agonist) – prime movers and assistant movers à help you move into the position you want o flexion / extension at the elbow joint o supination / pronation at the R/U joints • Stabiliser give compressive force to joint à shoulder flexion fast anterior translation/ clicking à you want to minimise this à stabiliser muscles prevent accessory movement • Antagonist – opposite action to mover therefore relaxes to allow movement à need to relax • Synergist – facilitates the desired movement by cancelling unwanted movements of the movers o supination and pronation e.g. pronator teres à pronates you, then brachialis (no rotation) elbow flexes you or use biceps but biceps wants to supinate so it uses pronator teres and quadratus to counteract unwanted movement à synergist

• 2 vectors • Rotational vector à how much the muscle causes a movement about a joint axis à what moves you • Translator vector à amount of compression or force that the muscle causes pushing that bone into the joint rather than creating a movement (stability) • Insertion of the end of arrow, origin is tip of arrow à insertion comes towards the origin • Rotatory vector is equal to the translator vector

• Blue line à insertion is closet to axis or rotation than the origin à translator vector is smaller than rotatory vector • Green line à insertion far away to axis than origin • Definition à spurt have insertion that’s close to AOR and a far origin • Shunt à origin is closer to joint AOR than insertion

• Muscles that have greater rotatory vectors than translator à spurt muscles à these create large and faster range of motion à biceps or brachialis • Shunt à larger translator vector than rotatory à provide a compressing force and stop/ shunt the accessory/ excess movements

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Biceps brachii – open chain o Proximal attachment is origin, distal attachment is the insertion o Shoulder à origin is very close to shoulder joint , insertion is far o Elbow joint à origin very far and insertion is very close o The elbow à biceps is a spurt BUT shoulder à biceps is a shunt Brachialis o Origin is half way down the shaft of humerus o Insertion is close to elbow joint o Spurt for the elbow joint Triceps (2 joint muscle but majority of muscle is on humerus) o Origin is far away from elbow, insertion is very close à spurt for elbow o Shunt for shoulder joint Anconeus o Axis of rotation is in the middle o So this muscle is relatively equidistant (more shunt than spurt if you really look at it)

Forearm and Wrist Flexors – Superficial Group • All originate from medial epicondyle (CFO) à all are weak elbow flexors à going into the forearm o Pronator Teres à attaches halfway along the radius o Flexor Carpi Radialis à goes to base of 2nd and 3rd metacarpals o Palmaris Longus à attaches to the palmar aponeurosis (piece of fasssia on arm) o Flexor Digitorum Superficialis à under the carpal tunnel and attach to the middle phalanx of second, third 4th and 5th phalanges o Flexor Carpi Ulnaris à attaches to pisiform and hook of hamate • In reference to the elbow à origin is extremely close to the elbows centre of rotation and insertion is far à thus collectively they shunt the elbow

Forearm and Wrist Flexors – Deep Group • This group of muscles do not have contributions at the elbow o Flexor Digitorum Profundus à doesn’t cross elbow, only down in forearm (profound does to the distal phalange) à muscle that originates far from wrist (same shunt / spurt- in the middle) o Flexor Pollicis Longus à starts halfway down the shaft (on the radius) then goes to the thumb (end of thumb) o Pronator Quadratus à wrist , pronator à centre of rotation is the distal radial-ulnar joint (pivot, synovial, uni-axial joint) § REMEMBER radius moves towards the ulnar so left part is insertion and right is the origin à both a shunt and spurt § Close to COR à compresses joint and provides stability Forearm and Wrist Extensors – Superficial Group • Except Extensor Carpi Radialis Longus, all attachment from lateral epicondyle (CEO) à all are weak elbow extensors o Extensor Carpi Radialis Brevis à under longus and attaches from lateral epicondyle o Extensor Digitorum o Extensor Digiti Minimi o Extensor Carpi Ulnaris o Extensor Carpi Radialis Longus à attaches under Brachioradialis (on humerus??) • Origin is really close to elbows centre of rotation , insertions at phalanges and metacarpals (near hand area) o Origin is close , insertion far à all are shunt Forearm and Wrist Extensors – Deep Group • Except Supinator, this group of muscles do not have contributions at the elbow. o Abductor Pollicis Longus à goes to thumb o Extensor Pollicis Brevis à attaches to thumb o Extensor Pollicis Longus à goes to end of thumb o Extensor Indicis à goes to the back of index finger o Supinator • None of them have elbow action • Supinator à lateral epicondyle attaches to supinator crest of ulnar and to the front at interosseous membrane o Origin is very close to COR (almost right on it) and insertion is far o So it is a supinator and stabiliser à shunt muscle

If hand is fixed and cant move à proximal moving to distal à closed chain Spurt and Shunt Muscles - Summary Spurt • origin far from joint, insertion close to joint • greater motion vector (perpendicular to bone) • mobility role Shunt • origin close to joint, insertion far from joint • greater compressive forces (along bone) • stability role

when will by body pick which muscle? Elbow flexion with load compared to unloaded? • • • • •

Simple basic task à primary main agonist depends on what movement we trying to achieve à unloaded, neutral, supination/ pronation elbow flexion à which muscle has the least number of unwanted movements Biceps à will supinate with you – going to supinate you so not ideal Brachialis à doesn’t pronate/ supinate cos it doesn’t attach to radius – can only elbow flex Brachioradialis à neutraliser – it’ll bring you back to neutral and elbow flex you à smaller than brachialis (cross sectional area) à original close, insertion far à shunt , not going to have a great rotatory vector The brachialis and Brachioradialis

Best muscle à brachialis (no load) it is a spurt – origin is far from cor insertion close at ulnar tuberosity, single articular muscle no unwanted movement in elbow and anywhere else also bigger muscle à large cross sectional area, small range but body selects this muscle as the primary agonist • Brachialis • • • •

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=> spurt / uniarticular / no synergist => largest cross sectional area => despite having small or smallest moment arm through range

INCREASE LOAD moment arm à greater the perpendicular line, the greater the moment arm is à another way to see how much movement it can provide à this is dependant on where the elbow is in space à if the elbow is straight down moment arm is reduced (especially for Brachioradialis) • • •

Brachioradialis à if the activity becomes difficult in some way à such as increase in load OR biceps If biceps are used we need pronator tres to cancel out the supination of biceps

Biceps brachii à likely next to be recruited, but tri-articular muscle, other action is supination => need synergist => pronator o ?? What position is the shoulder in à e.g. if at shoulder extension then the bicep would be disadvantaged – • Brachioradialis à same or slightly after biceps brachii to be recruited • Brachialis à increasing activation (of all muscles) àit will turn on more • Pronator Teres à acts as synergist for bicep’s supination and also an assistant agonist to flex elbow •

SPEED à Increasing speed (throwing/ tennis/ rapid movements) à There are forces that destabilise the joint causig the joint to separate and traction • Increases traction on the elbow joint (destabilises) • Recruit shunt muscles (Brachioradialis, CEOs, CFOs = stability) • Rapid alternating movements require both shunt activation and some co-contraction = stability Elbow joint: throwing

For the last deceleration you want muscles that are antagonistic to biceps à prevent elbow extension so you want flexors working eccentrically to slow that down – activating but lengthening • Triceps à working concentrically, decelerated by elbow flexors which work eccentrically and then concentrically again to bring arm back to starting position •

Muscle Recruitment Patterns – Effect of Joint Position Joint position (shoulder, elbow, radioulnar joints): • Mid range more efficient for muscle contractions à muscles are strongest, greatest moment arm and length tension is optimal • ~80°elbow flexion (moment arms greatest, length tension optimal) • Changing joint position changes gravity effects and therefore muscles used in actions (for both agonists and antagonists) à reduced moment arm • Starting position changes muscles used – e.g. in supination/ pronation à supinated uses biceps and brachialis , if pronated there’s no point of using biceps, turn on a synergist thus only use brachialis unless load is so big you need to recruit other muscles e.g. Shoulder position • Full elbow flexion with the shoulder held at 90°abduction in the coronal plane and in external rotation o 0°- 90° elbow flex: brachialis/ biceps concentric o 90°- 140° elbow flex: triceps eccentric

• If you do flexion like this at the same speed once you hit 90 degrees gravity will act on it so you need to slow it downà doing the opposite – slow it down – use triceps to slow down the motion to keep it smooth and working eccentrically to prevent forearm from crashing into you • Your brain is switching from elbow flexors to elbow extenders • If you do use biceps and brachialis that means you will speed up • If extending – you use flexors first and then extenders from 90 degrees – or it’ll just drop out Muscle Recruitment Patterns – Effect of Joint Position (2) eg. Radioulnar position • Performing full elbow flexion/extension from anatomical position in: o Pronation - brachialis concentrically/ eccentrically o Supination - biceps (+brachialis) concentrically/ eccentrically Muscle Recruitment Patterns – Laws and Principles Law of Minimal Muscleà This ‘Law’ was proposed by MacConaill M.A. and Basmajian J. in 1977. The basic tenet of this ‘Law’ is that muscles are recruited in such a way that synergistic activity is minimised. You also need to consider other factors affecting muscle recruitment. E.g. the degree of elbow flexion and/or forearm pronation associated with the activity. • Your body wants to minimise the amount of recruited muscles to be as energy efficient and make task as simple as possible • Body minimises no. of muscles and not to over recruit and minimise energy use • Depends on the complexity of task and the position you do it in Muscles do NOT work in isolation Although our brain aims to be most efficient by selecting the best muscle for the job, to minimise synergistic activity, it does not mean only one muscle is active and the other muscles that can also do the ‘action/job’ are non-active. In reality, there is a main agonist that will be the most active, and a number of secondary agonists (assistant movers) during activity. Which muscle/s will be the main agonist is determined by a number of factors (in no particular order): • joint position (large moment arm and muscle-length relationship)

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minimal synergistic activity large CSA uni/bi/poly- articular based on what movement is desired

reality à one or to main agonist, and then supporting ones and also synergist ones every movement we do à what are the agonist/ synergist/ stabilisers à to prevent excessive opening of joints QUESTIONS AT THE ENDDD OF LECTUREEE...