Quiz 2.1 Flashcards
Line of action
The line between the origin and insertion (tendon to tendon)
Muscle function
Generate force
How do you get a torque to be produced
The line of action does not intersect directly with the axis of rotation –> torque produced about joint it crosses
Force applied directly through AOR does NOT produce torque.
Torque
Tendency of a force to rotate an object about an axis
Units: Nm
T = F*(Perp. distance from axis)
Moment arm
Perp. distance from the LOA of muscle force to the center of the rotation of the joint
Depends on: origin/insertion and joint angle
As joint angle changes during movement, the moment arm length changes
T = F*(distance perp to force)
Lever arm
Distance from axis to perp. component of force
T = perp force*(distance)
Net joint torque
Summation of torques produced by all muscles acting simultaneously at a joint
Torque when concentric muscle action
Net joint torque is in the same direction as joint motion
ex: arm flexion
Torque when eccentric muscle action
Net joint torque is in the opposite direction as joint motion
ex: arm extension
Concentric internal/external torque
Internal T greater than external T
ex: Bicep torque greater than the dumbbell, you can lift it
Eccentric internal/external torque
External torque greater than internal torque –> lengthening
Isometric internal/external torque
Internal and external torques are equal, object remains stationary
Why is more muscle force necessary when muscle inserts at an angle instead of perp.
The moment arm becomes smaller due to the angle. See diagram
Lever
A simple machine consisting of a rigid body that rotates about an axis
Fulcrum
Point about a lever rotates (axis)
How are levers classified
By Axis, motive force, and resistive force
ARM
Mechanical advantage
MA = (Moment arm of motive force)/(moment arm of resistance)
Force moment arm > resistance moment arm
MA > 1.0
Not likely in body
Low force necessary to overcome resistance but resistance moved through limited ROM
Resistance M.arm > Force M.arm
MA <1.0
Most similar to body
Large force necessary to overcome resistance but moved through larger ROM
1st class lever
Axis between the motive force and resistive force (RAM)
Ex: elbow extension (Tricep-elbow joint- arm)
Plantar flexion
2nd class lever
ARM
Torque advantage (MA) usually exists for motive force (limited ROM)
Ex: Push-up
3rd class lever
AMR
most joints
Advantage in ROM and speed but disadvantage in force
ex: arm flexion, hip flexion, knee extension (quad inserts below knee)
Uniarticular
Muscles crossing one joint
Biarticular
Muscles crossing two joints
Multiarticualr
Muscles crossing multiple joints
Biarticulate muscles
Contribute to two joint torques simultaneously
Torque produced by muscle on one joint is dependent on angle of the other joint
Lombard’s Paradox
See slide
2 antagonistic muscles active in one movement but each muscle ends up being more active at a different joint therefore enhancing each other to complete the total movement
Biarticulate muscles can act like tendon
Shoulder ligaments
Superior acromioclavicular
Coracoacromial
Coracoclavicular
Coracohumeral
Capsular ligament
general function of ligaments
provide stability for the joints
Other shoulder structures
Articular cartilage
Glenoid labrum
Bursae
SLAP (Superior Labrum Anterior and Posterior) tear
Where the bicep tendon attaches to labrum
Causes: Heavy lifting, repetitive overhead movement like throwing, falling onto outstretched hand
Muscles of shoulder
Know functional relevance, go through slide tables of movement
Why do so many muscles cross the shoulder (structural and functional reasons)
Structural: Stability for the inherently unstable joint
Functional: The triaxial joint needs many muscles to perform all the movements of the shoulder. Many smaller muscles allow for greater DOF
Why does anterior and middle deltoid produce max force of muscles crossing the shoulder
Because arm’s function is to lift and carry which is primarily a movement in the front/middle of body.
** see table
Rotator cuff muscles
Supraspinatus, infraspinatus
subscapularis, teres minor
** see table
4 joints of the shoulder
Sternoclavicular, acromioclavicular, scapulothoracic, glenohumeral
Sternoclavicular joint
Condylar non-axial joint
articular disc
A/P sternoclavicular ligament and costoclavicular ligament
3 DOF (Elev/depress, protrac/retract, post rotation(Closed))
Acromioclavicular joint
Plane, non-axial joint
Articular disc
S/I acromioclavicular ligament, coracoclavicular lig.
Sloping interface leads to possible dislocation from lateral, superior force
3 DOF (Up (Closed)/down rotation, int/ext rotation, A/P tilting)
**See images for movements
Close packed
Maximum articulation between 2 bones in joint
Open packed
Minimal articulation between bones in a joint
Scapulothoracic joint
Not a true joint
Elevation/depress
Protract/retract
Up/down rotation
When is Sternoclavicular the axis for scapulothoracic
Elevation, protraction
When is acromioclavicular the axis for scapulothoracic
Downward rotation, internal rotation, upward rotation
Glenohumeral joint
Ball and socket, triaxial
G. Fossa points up and humeral head points up and back
