Introduction to Biomechanics IV: Kinetic Movement Systems

Question 1

Energy

Answer 1

• D: capacity to do work
• many types exist
• most interested in mechanical

Question 2

Mechanical Energy (ME)

Answer 2

-made up of PE and KE

Question 3

Kinetic Energy (KE)

Answer 3

• energy resulting from motion

- particularly dependent upon velocity

Question 4

Potential Energy (PE)

Answer 4

• capacity to do work secondary to position or form

- an object may contain stored energy because of height or deformation

Question 5

Strain Energy (SE)

Answer 5

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

Question 6

Friction

Answer 6

• necessary for movement
• D: force that potentially exists whenever two objects come in contact
• exists when one object slides over another
• vector
• 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

Question 7

Coefficient of Friction

Answer 7

• 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

Question 8

Linear Force Systems

Answer 8

• 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

Question 9

Concurrent Force Systems

Answer 9

• 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

Question 10

Concurrent Force Systems in Muscle

Answer 10

• 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

Question 11

Concurrent Forces and Types of Muscle Structure

Answer 11

• 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

Question 12

Concurrent Force Systems: Fusiform Muscles

Answer 12

• 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

Question 13

Concurrent Force Systems: Penniform Muscles

Answer 13

• 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

Question 14

Parallel Force Systems

Answer 14

• 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

Question 15

Rotary Force Systems

Answer 15

• torque
• levors
• force couples

Question 16

Torque

Answer 16

• 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

Question 17

Levers

Answer 17

• 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

Question 18

Levers Terminology

Answer 18

• 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
• MA=FA/RA
• the larger the MA, the easier the tast

Question 19

1st Class Levers

Answer 19

• 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

Question 20

2nd Class Levers

Answer 20

• 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

Question 21

3rd Class Levers

Answer 21

• 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

Question 22

Force Couples

Answer 22

• 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

Question 23

Force Couples in Body

Answer 23

• 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

Question 24

Tension Force

Answer 24

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

Question 25

Compression Force

Answer 25

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

Question 26

Shear Force

Answer 26

-applied parallel to surface

Question 27

Bending Force

Answer 27

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

Question 28

Torsion Force

Answer 28

• load applied about an axis

- twisting force

Question 29

Combined Forces

Answer 29

-more descriptive of what happens in nature

Question 30

Take Home Points

Answer 30

• 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