Introduction to Biomechanics IV: Kinetic Movement Systems Flashcards Preview

DPT 726: Orthopaedic Foundations > Introduction to Biomechanics IV: Kinetic Movement Systems > Flashcards

Flashcards in Introduction to Biomechanics IV: Kinetic Movement Systems Deck (30)
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-D: capacity to do work
-many types exist
-most interested in mechanical


Mechanical Energy (ME)

-made up of PE and KE


Kinetic Energy (KE)

-energy resulting from motion
-particularly dependent upon velocity


Potential Energy (PE)

-capacity to do work secondary to position or form
-an object may contain stored energy because of height or deformation


Strain Energy (SE)

-a form of potential energy
-mechanical energy due to deformation
-k in equation is proportionality constant
-delta x squared is distance material deformed



-necessary for movement
-D: force that potentially exists whenever two objects come in contact
-exists when one object slides over another
-point of application is to both objects
-line of action is parallel to contacting surfaces
-direction is oppositional to potential movement of object to which it is applied
-magnitude exists only if there is attempted movement, depends on the Rx force on each object and nature of surfaces
-not dependent on contact area
-coefficient of static friction > coefficient of kinetic friction


Coefficient of Friction

-describes the effect of different materials, roughness of contact surfaces
-the higher the coefficient the harder to overcome
-equation: Fx=mu x N
-N=normal force or force perpendicular to surfaces in contact


Linear Force Systems

-D: forces applied in same direction along same action line
-results in translatory motion
-may be in same or opposite direction
-sum of forces equals 0 in equilibrium and do not equal 0 when in motion
-vectors up and right give + values
-vectors down and left give - values


Concurrent Force Systems

-D: forces acting on one point but at different angles
-in same plane
-on same point
-not along same line
-net effect of all forces called resultant
-composition of forces allows for measuring resultant; solved graphically or via trigonometry
-effect of angle on magnitude of resultant (assume magnitude of forces remains constant)
-the greatest magnitude exists when forces act in the same line, in the same direction, and the angle between them is 0
-smallest magnitude exists when forces act in same line but in opposite directions and angle between them is 180 degrees


Concurrent Force Systems in Muscle

-muscles act as vectors
-magnitude equals the resultant of all fibers in that muscle
-direction and action line in direction of muscle fibers
-point of application usually distal segment


Concurrent Forces and Types of Muscle Structure

-muscles and muscle groups arranged with variety
-act individually or collectively
-produce very small movement or large, powerful movement
-shape and arrangement of fibers determine force generating capacity or shortening ability


Concurrent Force Systems: Fusiform Muscles

-parallel muscle fibers
-fascicles run length of belly
-fibers run parallel to line of pull
-known for high amount of shortening, high velocity movement
-can shorten 30-50% of resting length
-ex: tibialis anterior, biceps brachii, rectus abdominis


Concurrent Force Systems: Penniform Muscles

-fibers run diagonally to tendon running through muscle
-fiber force is different direction than muscle force
-feather shaped appearance
-secondary to short fascicles running at angle
-produce slower movements and more force
-trade off is increased physiologic cross-section leading to increased force
-ex: gastroc, deltoid, glute max


Parallel Force Systems

-D: system where forces are parallel and lie in same plane but don't have same line of action
-forces cause rotation around a stationary point
-resulting effect: rotation, translation, no motion


Rotary Force Systems

-force couples



-rotary application of forces
-causes movement around an axis
-T=Fr (r=perpendicular line of action of the force to the pivot point)
-torque produced varies according to length of moment arm



-application of parallel force systems
-D: machine that operates on principle of a rigid bar being acted upon by forces which tend to rotate the bar about a pivot point
-may be used to increase force, change effective direction of the effort force, increase distance


Levers Terminology

-F=effort or moving or holding force
-R=resisting force or weight
-A=point of pivot on axis
-FA=force arm or perpendicular distance from force to axis
-RA=resistance arm or perpendicular distance from resistance to axis
-MA=mechanical advantage or efficiency of lever
-the larger the MA, the easier the tast


1st Class Levers

-axis located between weight and force
-may be configured many ways: MA > 1, MA < 1, MA=1
-can use small effort to lift a large resistance
-may act at small distance to move resistance a great distance
-ex: cervical extensors


2nd Class Levers

-weight located between force and axis
-RA always smaller than FA
-MA always greater than 1
-can use small effort to move resistance, but it must move a greater distance than the resistance
-able to lift a large load with little effort
-ex: ankle plantarflexors
-less effort for a large resistance


3rd Class Levers

-force located between axis and weight
-FA always smaller than RA
-MA always less than 1
-force must always be greater than resistance
-what is loft in effort is gained in distance
-can move resistance a large distance (lots of ROM)
-ex: biceps brachii


Force Couples

-special parallel force system
-forces equal in magnitude but opposite in direction
-no linear motion occurs in pure force couple (steering wheel, bike handlebars)
-force couples in body are imperfect


Force Couples in Body

-lowering arm against resistance
-L dorsi and T major work as force couple with rhomboid
-other mm contributing: pec major, pec minor, levator scapulae, serratus anterior
-for flexion and abduction deltoid and rotator cuff work together
-r. cuff applies force to humeral head
-depresses and stabilizes head in glenoid fossa
-deltoid applies force to elevate humerus
-most evident in early abduction and flexion up to 90*
-relationship changes in upper range secondary to decreased r. cuff activity drops off
-direction of pull for various UE muscles in resting arm position demonstrated by picture on page 13
-contributions of each may vary for flexion, abduction, etc and phase of motion


Tension Force

-equal and opposite loads
-applied outward from surface
-greatest tensile force on plane perpendicular to load
-structure lengthens and narrows


Compression Force

-equal to opposite loads
-applied toward surface of structure
-maximum force perpendicular to plane
-structure shortens and widens


Shear Force

-applied parallel to surface


Bending Force

-applied load causes bend around axis
-tensile stresses/strains act on one side
-compressive stresses/strains act on one side


Torsion Force

-load applied about an axis
-twisting force


Combined Forces

-more descriptive of what happens in nature


Take Home Points

-application of kinetic principles helps us understand many aspects of human motion
-kinetic energy, potential energy, and friction contribute in unique ways to physical activity
-linear, concurrent, and parallel and rotary forces influence motion in subtly different ways
-six types of force-many times in combination-are seen in many types of healthy and pathologic human motion