biomechanical applications to joint structure + function Flashcards
what type of displacement is this:
- linear/straight line
- rare in human movement
translatory displacement
what type of displacement is this:
- angular
- movement of segment around a fixed axis
rotary displacement
curvilinear motion
2D joint motion
is the screw home mechanism an example of 3D or curvilinear motion?
3D
sagittal plane axis + direction of movement
x-axis (coronal)
flexion/extension
transverse plane axis + direction of movement
y-axis (vertical)
int/ext rotation
frontal plane axis + direction of movement
z-axis (anteroposterior)
ab/adduction
translation unit of measure
inches, feet, meters, etc
displacement per unit of time REGARDLESS of direction
speed
displacement per unit of time IN A GIVEN direction
velocity
measurements for…
linear velocity
angular velocity
acceleration
linear velocity (m/s)
angular velocity (deg/sec)
acceleration (m/sec^2 or deg/sec^2)
units of force (2)
newtons
pounds
force is directly proportional to…
mass and acceleration
what is the most consistent and influential external force
gravity
basic examples of internal forces
muscles
ligaments
bones
tendons
what is force represented by on diagrams
an arrow (vector)
vectors can represent which 2 types of forces
push
pull
COM in adults
S2
BOS in adults
between the feet
dynamic equilibrium
object moving at a constant velocity (zero acceleration)
“balanced forces”
t/f: unbalanced forces result in acceleration
true
newton’s 1st law
law of inertia
an object will continue in current motion until a force causes the speed or direction to change
when the sum of forces/torque are not equal to zero, then the object must be doing what?
accelerating
Newton’s 2nd law
law of acceleration
acceleration is DIRECTLY proportional to unbalanced forces/torques
acceleration is INVERSELY proportional to the mass (m) or moment of inertia (I)
moment of inertia is dependent on 2 things:
size of object
distribution of mass
2 or more forces work on the same segment in the same line
linear force systems
two or more forces work on the same segment from different angles
concurrent force systems
ex: quad and patellar tendon going from 90* knee flexion to extension
Newton’s 3rd Law
law of reaction
for every action, there is an equal and opposite reaction
how are tensile forces created
opposite pulls on the same segment/object
ex: joint capsule pulls up, ankle weight pulls down
tensile forces are ______ to the long axis of the segment/object
parallel
what force is perpendicular to the joint surface and leads to a slight separation of the joint + decreased pressure
joint distraction forces
ex: angkle weight on ankle in sitting (with foot hovering above the ground) puts distraction force on the knee + ankle joints
t/f: joint distraction forces can be dynamic or static
true!!
another name for joint reaction forces + an example
compression force
ex: foot up on leg press compresses the joint capsule
2 types of friction
static (F is less than Fs)
kinetic (F is greater than Fs + creates movement)
when is the magnitude of friction force the highest
just before the object starts moving
t/f: when there is more friction, more shear force is needed to move the object
true!!
note shear force is necessary in order to CREATE friction
what force resists the motion of solids or fluids sliding against each other
friction force
unaligned forces pushing one direction while an opposing force pushes in the opposite direction
shear force
Two forces equal in magnitude, OPPOSITE in direction, parallel and applied to the same object at different points
force couple
a force couple will always produce ______
torque
what type of movement is created by an isolated force through COM
translation
what type of movement is created by an isolated force NOT through COM
rotation and translation
what type of movement is created by 2 equal and opposite forces on opposite ends of an object
rotation
Torque = _____x_____
magnitude of force x moment arm
how does an increased moment arm impact torque
increases torque
CW is indicated with __(+/-)__ while CCW is indicated with __(+/-)__
CW = -
CCW = +
torsional moments
rotation of segment around its long axis (twisting motion)
spiral fracture is an example of ______ moments
torsional
transverse fractures are examples of ______ moments
bending
the direction of pull for any muscle is toward…..
the center of the muscle
______ occurs when the torque of a muscle exceeds opposing torques
movement
benefit of anatomical pulleys + one classic example in the body
increases moment arm which reduces the amount of force necessary to overcome the baseline torque
(bc remember torque = force x moment arm)
ex: PATELLA IN KNEEE ((:
1st class lever + an example
axis in between effort force (EF) and resistance force (RF)
think about seesaws!!
ex: flex/ext head (axis = neck)
2nd class lever + an example
resistive force (RF) is in between the axis and effort force (EF)
think about wheelbarrows!!
ex: calf raises (axis = forefoot)
which lever system (classes 1,2,3) is the most powerful one
2nd class levers
3rd class lever + an example
effort force is between axis and resistive force
ex: elbow flex/ext
what is the most common lever system in the body
3rd class levers
mechanical advantage equation
MAd = EA/RA
EA = effort force of moment arm
RA = resistance force of moment arm
what does it mean when the mechanical advantage is greater than 0?
less effort is required to move the lever
in a 2nd class lever, __(more/less)__ angular displacement and velocity is gained.
LESS!!
the amount of effort is directly correlated with amount of displacement and velocity
(1st and 3rd class levers have MORE angular displacement/velocity and MORE effort)
the translatory, parallel component in force resolution
Fx
the rotary, perpendicular component in force resolution
Fy
which component (Fx or Fy) has a much greater force than the other in most muscles
Fx
t/f: the angle of application of most muscles is large
FALSE, it is small
a large angle of application would mean more joint stress + movement insufficiency since more force would be required to achieve the same amount of rotation a smaller angle needs
as a PT, is it harder or easier to push on a leg with a long moment arm
EASIER!!
the longer the moment arm, the easier it is on external forces vs harder on internal forces
(decreases effort for PT to lengthen MA)
why must Fx and Fy forces need to be balanced before rotation can occur?
if they are not, unbalanced translatory forces (linear Fx/Fy) can cause distraction forces, shear forces, or joint compression
this creates joint instability and could lead to injury/wear and tear
open chain movement
distal end of the segment is free to move
close chain movement
distal end of the segment is fixed
