Biomechanics Quiz 3 Flashcards
cartilage: chondrocytes embedded where?
within extracellular matrix
cartilage: extracellular matrix is made up of what 2 things and what % each are they?
- water 60-80% (hyaline)
2. collagen 10-30% (hyaline)
which part of extracellular matrix is framework?
collagen
extracellular matrix functions:
- protect chondrocytes (inside framework)
2. reduce movement friction
cartilage: vascular or avascular?
avascular – no blood supply
cartilage: what helps diffusion from synovial fluid?
joint loading
what aspect of articular cartilage allows it to withstand normal loads?
“self-renewing”
how are cartilage fibers laid down?
in different directions depending on each layer
T/F … it withstands loads in multiple directions.
TRUE!
How many zones can articular cartilage be divided into?
4 zones
Under articular cartilage is what bone?
Sub-chondral bone
Above articular cartilage is what?
synovial fluid
What is the zone at the very top below synovial fluid?
superficial zone
cartilage: mechanical behavior resembles what?
a sponge
tendon and ligaments are similar or dissimilar in structure?
similar!
tendon + ligaments: made up of what 3 things:
water
collagen
elastin
tendon and ligaments: % water, % collagen, and % elastin
70% water
25% collagen
5% elastin
what is the main difference between tendons and ligaments?
arrangement of collagen fibers
tendons are bound together in what direction?
parallel
ligaments are bound together in what direction?
nearly parallel
cartilage is bound together in what direction?
mixed arrangement
tendon + ligament: strength in general
both have strong tensile strength
how are tendons and ligaments under compression and shear?
little resistant to compression and shear
ligaments strength compared to tendon strength
less strong under axial tensile loads
why ligaments strength compared to tendon strength is less under axial tensile loads?
higher amounts of elastin and collagen arrangement.
which can carry loads better that are not purely axial and why?
ligaments are better because of their collagen arrangement!
what are the 6 forces?
gravity torque shear compression friction strain
what is a force?
push and pull of one object on another
what does it mean that forces come in pairs?
the force exerted is matched by an equal but opposite directed force
newton’s third law of reaction:
for every action, there is an equal and opposite reaction
force can be described as a vector – what does that mean (3 things)?
it has:
magnitude
direction
point of application
properties of forces affect 3 things:
- characteristics of performance
- ability
- risk of injury
what is derived from the vector addition of two or more forces
resultant force (net force)
what a force actions on an object, there are 2 effects possible:
- object acceleration
2. object deformation
factors that influence whether injury occurs when external force is applied to body:
- magnitude
- direction
- area
- material properties of loaded body tissues
action of forces: make what assumption?
often assume forces cause minimal deformation
relationship between net force (F), mass (m), and acceleration (a) a center of mass?
what are the units in each?
F=ma (Newton’s 2nd law)
N = kg*m/s2
Newton’s 1st law
An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
3 basic types of applied forces
- compression
- tension
- shear
Compression
pressing or squeezing force directed normal (perpendicular) to a surface
DOWN!
Tension
pulling or stretching force directed normal (perpendicular) to a surface
UP!
Shear
sliding or tearing force directed parallel to a surface
HORIZONTAL!
Bending
tension on one side of an object and compression on the other
*Asymmetric!
Bending: forces per unit area that are greatest at the surface
compressive and tensile
torsion - definition. what does it create?
Load producing a twisting of an object.
Creates a shear within object.
Contact forces - definition
Forces pushing or pulling on an object due to contact with another object
NOTE: there will be a contact force anywhere two objects touch
Contact forces in biomechanics include:
- external
2. internal
Non-Contact Forces
Forces that do not result from direct physical contact (e.g.force of gravity)
External Forces:
produced by a material in response to an outside energy source
A common type of passive force
Normal Reaction Force
example of Normal Reaction Force
Ground Reaction Forces: Human Movement
Internal Forces:
Forces generated by an internal energy source
Draw ground reaction forces
** DRAW THEM **
include:
heal strike
push off
toe off
label time axis (x)
% force (y)
Ground reaction force resolves into 3 components
- vertical
- antero-posterio
- medio-lateral
Fr
Ground reaction force
Arrow coming up from the bottom of the foot.
Fg
Force of gravity
Always pushing down.
Fd
Aerodynamic drag force
Always going against the grain / direction of movement of the body (i.e. if the body is moving forward, the arrow is pointing backward).
the dot in the graph of ground reaction forces - the runner
The dot is the center of mass of the person / object.
Classifying forces – internal forces
- forces that act within the object or system in motion
2. action and reaction forces act on different parts of the body.
Classifying forces – 4 different types of internal forces
- joint contact
- musculotendon
- ligament
- resultant joint
Joint Contact Force: definition and example in body
compressive force resulting from bone-on-bone contact (2 articular surfaces)
associated with: load-bearing by skeleton
NOTE: always compressive
EXAMPLE: pelvis and femur contact
Musculotendon Force: definition, function, and force produced
active and passive forces generated by a muscle-tendon unit
Function: to create / resist movement at joint
Force produced: tensile forces in direction of tendon angle of insertion
Ligament Force: definition, function, and force produced
passive force produced bystretching of a ligament
Function: to prevent excessive motion at joint
Force produced: when stretched, tensile force on bone at attachment
Resultant Joint Force
net force acting across ajoint (due to all sources) – sum of all forces acting at joint
NOTE: contact and muscle forces acting at a joint CANNOT be determined individually
*Just add up all the vector arrows and that is what direction the force ultimate goes in
Motion definition (kinematics)
action or process of a change in position.
Moving definition (kinematics)
change in position from one point to another.
Movement (kinematics)
change in position
Linear motion
“translation” or accessory motion that occurs when all points move the same distance in the same direction, at the same time
Angular Motion
“rotary motion” or “rotation” that occurs hone all points move in circles (or circle parts) around the same central axis.
basic def:
- degrees of freedom
- axis of rotation
NOTE: axis is inside or outside the body
Angular Kinematics & Motion
Movement performed through rotation of the body segments
Angular Kinematics & Motion – the body is often analyzed as what?
… a collection of rigid, rotating segments linked at the joint centers
Measuring Angles - intraradial
against the body
Measuring Angles - interradial
??? within the body? outside the body?
Joint Angles
Relative angles between adjacent body segments.
OR
Rotation of distal segment relative to proximal
joint angle of 0 - what position?
anatomical position
