Levers and Mechanical Advantage Flashcards
What is a lever?
any rigid segment that rotates around a fulcrum
When does a lever system exist?
when two forces are applied to a lever that produces opposing torques
Levers to bony segments produce net rotation by what two forces?
gravitational force and muscle force
What is the force that is producing the resultant force?
effort force
What is the moment arm for the effort force?
effort arm
What is the force that creates an opposing torque?
resistance force
What is the moment arm for the resistance force?
resistance arm
What is the force acting in the direction of rotation?
effort force
Which of the following does not determine the class of a lever?
a. position of the axis
b. size of object
c. size of effort arm
d. size of resistance arm
B
What kind of lever has an axis that lies between the point of application of the effort force and the resistance force?
first class
What kind of lever has a point of application of a resistance force in between the axis and effort force?
second class
What kind of lever has a point of application of an effort force between the axis and resistance force?
first class
Which class of lever has a larger effort arm than resistance arm?
2nd class
Which class of lever has a larger resistance arm than effort arm?
3rd class
Name some examples of a first class lever.
scissors, Cervical extension, lumbar flexion, see saw
Name some examples of a second class lever.
Plantar flexion, nut cracker, bottle opener, push up
Name some examples of a third class lever.
fishing pole, elbow flexion, knee flexion
What is measure of the mechanical efficiency of a lever system or the relative effectiveness of the effort force in comparison with the resistance force?
mechanical advantage
What does mechanical advantage provide an understanding of?
the relationship between the torque of an external force and the torque of a muscular force
What is the formula for mechanical advantage?
EA/RA
What does it mean when mechanical advantage is above 1?
effort arm is larger than resistance
How can you change the mechanical advantage?
changing the length of the effort arm or resistance arm
True/False: Mechanical advantage of levers within the body can change.
False - due to the fixed attachments it cannot
What is the mechanical advantage of a first class lever?
greater than, less, than or equal to 1
What is the mechanical advantage of a second class lever?
greater than 1
What is the mechanical advantage of a third class lever?
less than 1
True/False: Torques on human segments are produces by muscles and external forces.
False - they result from vertical and horizontal forces produced by muscles and external forces occur
Which of the following does not increase torque?
a. increase the magnitude
b. apply the force perpendicular
c. decreasing the weight
d. increase the distance of the point of application of the force from the joint axis
C
True/False: Changes in external load increase the magnitude of torque, therefore, the torque required.
true
True/False: Even though load of a human segment cannot be changes, can be manipulated.
True
What change occurs when moving from anatomic standing to shoulder flexion in lumbar flexion?
LoG falls through axis of rotation = reduced extension torque needed to overcome flexion
In the following three motions, where is torque the highest?
- normal
- shoulder flexion 180deg
- shoulder flextion 90deg
3
In what position in supine shoulder flexion is extension torque the highest?
arm at side
In what position in supine shoulder flexion is flexion torque the highest?
180deg flexion
In prone shoulder flexion, when is flexion torque maximized?
arm at side
In prone shoulder flexion, when is extension torque maximized?
180 deg flexion
In which of the following options requires more effort?
horizontal abduction to shoulder flexion
normal to abduction
normal to abduction
What are the components of total force?
perpendicular (Fy) and parallel (Fx)
When the force applied to a lever is above or below 90 degrees, what happens?
the component that is applied @ 90 degrees will continue to contribute to rotation
What force will tend to create vertical translatory motion?
Fx
What force will create rotation and tends to also create horizontal translation?
Fy
What does most of the force generated by a muscle contribute to?
joint compression (rather than rotation) = enhances joint stability but means a muscle must generate a large total force to produce efficient torque to move through space
Rotation around a joint axis requires the sum of the parallel (and perpendicular) components equals zero. What will happen if not?
translatory motion will continue (alone or in combo w/ Rotation) until checked by a capsuloligamentous force or by a joint reaction force
The majority of torque on a segment will be produced by forces (or force components) that are applied at what degrees to the segment?
90
True/False: The greater the net unbalanced torque, the greater the angular acceleration of the segment.
True
What is an open chain?
one end of a segment (or set of) is free to move in space
What is a closed chain?
both ends of a segment (or set of) are constrained in some way and are not free to move in space
Which type of chain is independent? Which type of interdependent?
open, closed
Which type of chain allows isolation?
open
What is the WBing status for each type of chain?
closed = WBing, open = NWBing
Which type of chain favors stability? Mobility?
closed, open
Which type of chain favors upper extremity function? Lower extremity?
open, closed
Give an example of exercise for open chain.
knee extension
Give an example of exercise for closed chain.
leg press
What effect does knee extension exercise have?
places direct tensile stresses on knee joint capsule and ligaments when hanging freely, increased stress on the ACL as knee approaches full Ext, reduced joint compression
What effect does leg press have?
reduced tensile loading on knee joint capsuloligamentous structures, increased stress on PCL as knee approaches 90 deg flexion, increased joint compression, increased potential for substitution
