Lecture 6 - elbow muscles

recruitment of flexor muscles

- biceps activated as an elbow flexor with the forearm supinated regardless of the speed of flexion or the resistance - when the forearm is partially pronated, the biceps is only recruited with resistance - in full pronation, the biceps will only be partially recruited with resistance - brachialis is active under all conditions of elbow flexion due to its distal attachment on the ulna; able to move the elbow through a full range of motion due to its short moment arm - brachioradialis is active with resisted elbow flexion, especially when the forearm is partially and fully pronated; functions against resistance even when the forearm is supinated - brachioradialis compensates for inefficiencies of biceps in pronation - pronator teres is recruited as an elbow flexor when resistance is applied

brachialis

1 joint muscle elbow flexor - very strong (large cross section) sits under biceps only works as flexor - no synergists needed From mid humerus shaft to ulna tuberosity and coronoid process of ulna - Shunt muscle - power Works as flexor under ALL conditions always active as a flexor attached to ulna so power not effected by pro/sup works best when arm flexed (90 degrees)

forearm supinators

1. Supinator (prime mover) 2. Biceps Brachii (assistant mover - effective when flexed to 90 degrees) 3. Brachioradialis (returns to mid position from pronation)

extensors of elbow (SAT)

1. Triceps brachii (olecranon of ulna)(*2 joint muscle - extends shoulder, extends elbow) 2. Anconeus (weak extensor) 3. Supinator (* 2 joint muscle - extends elbow, supinates forearm)

flexors of elbow (BBBPP)

1. brachialis (prime mover - spurt) (1 joint muscle * only flexes elbow - attached to ulna tuberosity) 2. biceps brachii (assistant mover - spurt) (*3 joint muscle - shoulder flexion, elbow flexion, forearm supination) 3. brachioradialus (shunt - stability) (lateral epicondyle/ radius styloid) (*2 joint muscle - flexes elbow, supinates & pronates forearm) 4. pronator teres (weak flexor)/ (*2 joint muscle - elbow flexion, forearm pronation) 5. pronator quadratus With speed or load ( all muscles recruited)

forearm pronators (must attach to radius)

1. pronator teres (also an elbow flexor- strength effected by arm position - 2. pronator quadratus 3. Brachioradialis (return to mid position)

Muscle recruitment patterns - effect of speed

Add Speed (pitching a ball overhead/tennis/hammering) Arm wants to keep going so need shunt muscles to stabilise Brachioradialis (active as shunt) CFO (medial epicondyle) CEO (lateral epicondyle) When arm flexed Triceps concentrically contract - to extend arm at end range (ball thrown) need to decelerate quickly Biceps and brachialis will eccentrically contract (slow down & control mvt) Also need shunting muscles (compression) at end of range brachioradialis & CFO (stability) will eccentricaly contract

Compartments of forearm muscles

Anterior compartment - flexors and pronators Posterior compartment - extensors and supinators

brachioradialus

Bi-articular (elbow and wrist) 1. wrist flexor 2. elbow flexor 3. from pronated position it will supinate (pull back to neutral - mid postion) Shunt muscle - stability/compression (insertion far from joint) humerus to radial styloid process (distal) More active 1. with speed 2. if load and arm midway or pronated ++ compensates for ineffectiveness of biceps when it is pronated - brachioradialus will take over with load 3. inhibited as a flexor if arm is supinated fully (swtich off) Very active 1. rapid change from pronation to supination eg. screwdriver Other muscles more active if elbow is at angle (biceps, brachialis)

what happens to biceps brachii when using screwdriver?

Biceps brachii is very active when elbow is flexed and high powered supination needed triceps will have to be active to hold elbow at flexed position (stationary at 90 degrees) - triceps will cancel out the unwanted flexion of biceps

Muscle recruitment patterns effect of joint position

Flex in full pronation - Biceps inhibited Brachialis will be most active Flex in full supination - Biceps very active Brachioradialis is inhibited as a flexor

Muscle recruitment effect of gravity

Flexion & extension with bicep curl if no load (but gravity working) Elbow flexors (concentric contraction coming up - working against gravity) and (eccentric contraction going down - resisting gravity) if add speed (fast) Elbow flexors (concentric contraction of flexors the whole way)

Elbow flexion recruitment of muscles (midway) Half pronation/ half supination

Hand is midway (sup/pro) and unloaded 1. brachialis (Only flexes / uni-articular / no synergist needed) - always active, spurt muscle, large cross section so powerful 2. biceps brachii (very active if loaded) (spurt muscle, prime mover, tri-articular - also does supination so need synergist) 3. pronator teres (will pronate to cancel out supination of biceps - act as synergist to biceps) 4. Brachioradialis (shunt muscle - for stability) last to be recruited if needed If add load = maximum response from all If full pronation = switch off bicep brachii / increase activity of brachialis if full supination = switch off brachioradialis (stops working as on lateral side of forearm and cant flex in this position)

Common Flexor Origin CFO

Muscles attached to medial epicondyle flexors of wrist and fingers

shunt muscle

Origin close to joint Insertion far from joint Assistant movers Compression (insertion moves to origin) Large compression force (stability) short rotational component greater compression forces (pull along bone) eg. brachioradialis (insertion at wrist) common flexor origin (medial epicondyle)

spurt muscle

Origin far from joint Insertion close to joint Prime movers Force (insertion moving to fixed origin) apply force creating movement Large rotational component (Motion) Short compression component Greater motion vector (perpendicular to bone - pulling up) prime movers Biceps brachii brachialis triceps brachii

pronator quadratus

Pronator - prime mover - uni-articular distal anterior ulna to distal anterior radius (across wrist) Most active pronator active under all conditions

What muscles will dynamically stabilise elbow with rapid alternating movements?

Shunt muscles - stability Brachioradialis (origin close/ insertion far away) CFO - muscles attached to medial epicondyle and attach at wrist or hand)

Supinator

Very deep at posterior of arm - wraps around radius elbow extensor (assitant mover) - not strong extensor Supinator (Prime mover) - always active regardless of angle, speed or load Helped by bicep brachii to supinate lateral epicondyl & supinator crest of Ulna to proximal shaft of radius

anconeus

elbow extensor (assitant mover 10%) small muscle at posterior of elbow lateral epicondyle to posterior ulna/olecranon process of ulna Uni-articular All it does is extension

pronator teres

elbow flexor (assistant - active with load) pronator (reserve pronator - active with speed and force) medial epicondyle/ supracondyl ridge to proximal radius (at oblique angle) position of elbow no effect Need synergist when pronating to cancel out unwanted flexion - triceps act as synergist co-synergists = pronator teres/ triceps

triceps brachii

long head (infraglenoid) More medial lateral head (posterior humerus - lateral to spiral groove) middle head (Posterior humerus - medial to groove)(can be seen just above elbow - surface anatomy) insert olecranon process of ulna 2 joint muscle - long head is bi-articular (extension shoulder/ extension of elbow) Spurt - prime mover Always first extensor activated Activity unaffected by forearm position

biceps brachii

long head - supraglenoid of glenoid fossa short head - coracoid process of scapula insertion - radial tuberosity of radius 3 joint muscle - GH, Elbow, radioulnar 1. Shoulder flexion 2. elbow flexion 3. supination spurt muscle - power (origin far from elbow joint) As elbow flexor 1. more efficient when shoulder neutral 2. more efficient when forearm is mid position or supinated (as attached to radius its power effected by sup/pro) ++Biceps inhibited when pronated - so will only be active if load or speed ++Biceps always active when supinated 3. more efficient when elbow flexed (>80 degrees) 4. with load active in all positions Will need synergist if flexing - to cancel out bicep wanting to supinate (pronator teres) As supinator 1. Very powerful - from full pronation can spin radius sharply into supination 2. powerful as 3 times larger than supinator 3. most effective as supinator when elbow flexed to 90 degrees

Common Extensor Origin CEO

muscles attached to lateral epicondyle extensors of wrist and fingers

cubital fossa

superior border - imaginary line b/t medial & lateral epicondyles Medial border - pronator teres Lateral border - brachioradialis Floor - deep - brachialis/supinator

Why is brachioradialis preferred dynamic stabiliser of elbow during rapid alternating elbow flexion and extension when hammering a nail into wall?

will contract eccentrically (lengthen) to control rate of extension needed to hit nail provides compression force - stop biceps dislocating radius

muscle coupling

• Biceps +Triceps + supinator - supination is allowed while preventing elbow flexion/extension • Pronator teres + triceps - pronation is allowed while preventing elbow flexion/extension