Week 1 Flashcards
DEGREES OF FREEDOM
Number of independent directions of movement
Can have up to three degrees of freedom (corresponding to 3 cardinal
planes)
Stability vs mobility
AXIS OF ROTATION
Pivot point about which motion is occurring
In what plane does the axis lie?
Importance of knowing the location of axis of rotation
The plane of the axis of rotation is perpendicular to the plane of the osteokinematic
motion
Able to determine muscle actions – Application!!!
Translation
surface to surface motion
linear motion
arthokinematics: slide
Rotation
circular motion
osteokinematics:
flex/ext = sagittal
ab/adduction = frontal
int/ext rotation = transverse
arthrokinematics:
roll spin
Internal force
muscles - active and passive
Can be active (stimulated muscle under volitional control) or passive (generated by tension in stretched periarticular
connective tissues, such as intramuscular fascia, ligaments, joint
capsule)
ligaments and tendons
joint capsules
compression force
tension
shear force
External force
COM
Friction
Gravitational force – pulling on mass of body, a body segment,
or an external load
Contact force – push, pull
MechA =
IMA/EMA
Kinematics
Branch of mechanics that describes:
* Motion of the body (joints) without regard to forces or torques that may
produce motion
2 types of motion
* Translation – Linear motion
* Rotation – Angular motion
Translational/Linear motion
Joint surface to surface motion- all parts of a body/segment move parallel to and in the same direction as the other parts of a body/segment (can be in a
straight line or curved path)
* Sliding in knee extension
Rotational/Angular motion
Circular motion
Body moves about a pivot point, so all points of the body simultaneously rotate
in the same angular direction
Motion of two adjacent long bones relative to each other
Axis of rotation
Pivot point for the angular motion
Center of rotation
* Changing throughout joint movement
* Bones rotate about a joint in a plane that is perpendicular to the axis of rotation
Osteokinematics
Motion of bones relative to the 3 cardinal planes of the body (person in
anatomic position)
Movement can occur in 2 different ways
* Proximal segment can rotate against the relatively fixed distal segment (closed chain)
* Distal segment can rotate against the relatively fixed proximal segment (open chain)
- “Knee flexion” describes “relative motion”;
- Does not tell you which segment is moving
-i.e. tibial on femoral or femoral on tibial
open chain
proximal segment fixed
distal segment free
closed chain
proximal segment free
distal segment fixed
Kinematic chain
refers to series of articulated segmented links
i.e. scapula, humerus, ulna/radius, carpals
Closed chain
the distal end of the extremity is fixed to the earth or other immobile object
e.g. squat, pull up
Open chain
distal end of the extremity is not fixed and is free to move
e.g. knee extension machine, bicep curl
Arthrokinematics
Describes motion that occurs between the articular surfaces of the joints
Joint surfaces range from flat to curved
One surface usually relatively convex, one concave
Helps to improve joint congruency, dissipate forces by increasing the
surface area, and guide the motion between bones
3 fundamental arthrokinematic movements:
spin
roll
slide/glide
Spin
Bone can also rotate by spinning its articular surface against the articular surface
of another bone (radio humeral joint)
Roll and glide
Rolling convex surface typically involves slide in the opposite direction
Many joints combine rolling and slide with spinning (e.g., femoral on tibial knee
extension the femur spins internally as the femoral condyle rolls and slides on the
relatively fixed tibia)
Convex-Concave Rule
Direction of arthrokinematics rolling and sliding motion
It depends on which surface is moving
Convex moving on Concave
Rolling and sliding are in the OPPOSITE direction
Concave moving on Convex
Rolling and sliding are in the SAME direction
Passive tension-
helps joint stability and
reduces passive accessory movement
Taut pubofemoral Ligament
From Extension and abduction
Taut ischiofemoral Ligament
From extension and internal rotation
Taut iliofemoral
Ligament from
extension
Line of gravity
(LOG)
causes
extensor torque,
counterbalanced
by passive flexor
torque of hip
ligaments
Close-packed vs. Loose-packed position
A joint is most stable at its close-packed position
A joint is most mobile at its loose-packed position
Joint stability can also be achieved by active muscle forces
The close-packed position is when
Articulating surfaces are maximally congruent
Ligaments or capsule are pulled tight (passive tension)
Impact of forces on the MSK system
A force that acts on the body is referred to as a load
Forces or loads that fixate or stabilize the body can also deform or injure the body
Open chain movement
The prime mover is usually muscle force
Decreased co-activation of antagonist muscles
Closed chain movement
The prime mover is gravity when the body is moving toward the
Earth
The prime mover is when the body is moving away from the
Earth is often defined in terms of muscle groups
Increased co-activation or eccentric activation of antagonist
muscles
Increased loading on the joint
Kinetics
describes the effect of forces on the body
(force – a push or pull that can start, stop,
or modify movement)
Newton’s 1st law of motion
(sumF = 0)
A body remains at rest or in constant
linear or angular velocity except when
compelled by an external force to
change its state
Objects in equilibrium….for example, consider a
hockey puck resting on ice; the forces are (=)
After the puck is struck, it is accelerated and will
again be in equilibrium until another force acts on it
Newton’s 2nd law of motion
quantity of the force is = to the product of the mass that received the
force and the acceleration of the mass
F = ma
the acceleration of a body is proportionate to the magnitude of
the resultant forces (F) on it and inversely proportionate to the mass (m) of the body
Unit of force is a
(N)
1N= 1kgX 1m/sec2
Newton’s third law of motion
action and reaction
For every action force there is an = and
opposite reaction force
The state of motion of a body depends on
the forces acting on that body (vs the
forces it may exert on other bodies)
Walking up slippery icy driveway
External force: Gravity
(concept of COG)
Center of mass – point in every body or object
about which the mass is evenly distributed
Human body COM is just anterior to S2 when standing
Gravity acts on the center of mass of the body
segment or an object
When subjected to gravity, the COM is referred to
as the COG (weight is the effect of the acceleration
of gravity on a mass – (Wt=m*G)
Center of mass (COM)
During movement, the COM is continually changing
The location being a function of the size and
location of the individual body segments
Concept of COG
The direction of the external
force due to gravity is
referred to as the line of
gravity (LOG)
Forces can stabilize joints and body
Newton’s 1st law of motion (sumF = 0)
Forces can produce body motion
Newton’s 2nd law of motion (sumF = ma)
Action and reaction
Newton’s 3rd law of motion
Internal and external forces counterbalance each other to:
control body movement (sumF=Fi+Fe=ma)
maintain stability (sumF=Fi+Fe=0)
Each force (internal and external) is depicted by an arrow that represents a vector
Vector is described by its:
> Magnitude
> Direction (commonly referred to as the line of force and line of
gravity)
> Sense (indicated by arrowhead) depicting whether the force is
acting upward (positive) or downward (negative)
> Point of application of the force
Torque
rotatory equivalent
of force
Product of the force x perpendicular distance (d) from the line of action to the axis of motion. So, (τorque =F * d)
Forces acting a distance from the axis of rotation will produce rotation at the joint
Moment arm
Torque = Force x moment arm
Force pushes/pulls in a linear fashion, torque rotates an object about an axis
Moment arm
the shortest distance from the force vector to the axis of rotation
Internal moment arm (IMA)
External moment arm (EMA)
Levers
Simple machine consisting of a rod suspended across a
pivot point
Converts force into torque
Leverage describes the relative moment arm (MA) possessed by a particular force; the longer the MA, the
greater the leverage
Musculoskeletal Levers
Internal and external forces produce torques
through a system of bony levers
Internal and external torques counterbalance
each other to produce motion or to achieve
stability of these levers
Motion: sumT = Ti + Te = Iα (angular acceleration)
Newtons second law
Stability: sumT = Ti + Te = 0
3 classes of levers
1st class levers can have a MechAdv =, <, or > than 1
2nd class levers always have an MechAdv> than 1
3rd class levers always have an MechAdv <1
Mechanical advantage
(Mech Adv) of msk
lever is defined as the ratio of the Internal
moment arm (IMA) to the length of the
External moment arm (EMA)
