Intro to Biomechanics Flashcards
What is kinesiology?
- the study of movement
- what happens with the body during movement
What is biomechanics?
- the study of forces applied to the outside and inside of the body and the bodies reaction to those forces
- uses physics
What is the difference between kinematics and kinetics?
Kinematics:
- describes motion of the body WITHOUT regard to the forces/torques that may produce the motion
Kinetics:
- describes the effect of forces on the body
- includes forces, torques, physics principles
Is naming the plane of motion considered part of kinetics or kinematics?
kinematics
- it focuses on the movement of the body WITHOUT taking force into account
What are rotary movements?
- this is an angular displacement (uses a pivot point)
- rigid body moves in a circular path around a pivot point
- ROTATE in same angular direction and same number of degrees
measured in degrees or radians
What are translatory movements?
- this is linear displacement (gliding or sliding)
- all parts of a rigid body move parallel to and in the same direction
- Rectilinear (straight line) or curvilinear (curved line)
- measured in meters or feet
What are the main differences in how rotary and translatory motions are performed in the body?
Rotary:
- more from muscle stimulation
Translatory:
- are more passive
What is an axis of rotation?
- pivot point for angular motion
- usually through a joint (or very close to it)
What is an evolute axis of rotation?
- a migrating axis of rotation
- AoR will stay in one place only if bone is completely circular
How does active movement differ from passive movement?
Active: caused by stimulated muscle
Passive: caused by sources other than stimulated muscle (therapist does movement)
Explain the frontal cardinal plane
splits body/body part into anterior and posterior (front and back)
What axis of rotation is usually associated with the frontal plane?
- sagittal AoR
Explain the sagittal plane
- splits the body/body part into left and right halves
What axis of rotation is usually associated with the sagittal plane?
- frontal AoR
Explain the transverse (horizontal) plane
- splits the body/body part into superior and inferior (top and bottom)
What axis of rotation is usually associated with the transverse (horizontal) plane?
- vertical AoR
What member of the joint does the AoR usually run through?
- usually the convex member of the joint
What is degrees of freedom?
- number or independent directions of movements allowed at a joint
- can have up to 3 degrees of freedom that corresponds with the cardinal planes
What usually occurs if a joint loses a degree of freedom?
- this greatly inhibits the joints normal function
Define a uniaxial joint
- 1 plane
- 1 axis
- 1 degree of freedom
Define a biaxial joint
- 2 planes
- 2 axis
- 2 degrees of freedom
Define a triaxial/multiaxial joint
- 3 planes
- 3 axis
- 3 degrees of freedom
What is osteokinematics?
- motion of bones relative to the 3 cardinal planes
- movement occurs b/w shafts of 2 adjacent bones as they move
- PROM (rotary)
What is arthrokinematics?
- motion that occurs b/w the articular surfaces of joints
- focuses specifically on the minute movements occuring within the joint and b/w joint surfaces
- joint mobilizations
- rotary or translatory
What is meant by end feel?
- a joints resistance to further motion
- dictated by joint structure
What are some normal and abnormal end feels?
Normal:
- hard or bony
- firm or capsular
- soft
Abnormal:
- empty
- pain until end of motion
- anything that is abnormal for that joint
What is the difference between open and closed chained kinematic movements?
Open:
- distal segment free
- usually distal on proximal
- kicking
Closed:
- proximal segment free
- usually proximal on distal
- pushups
What movements are considered arthrokinematic movements?
- Roll
- Slide
- Spin
What is the Convex-Concave rule?
Convex-on-concave
- roll one way
- slides the opposite way
- must occur in order to stay in the joint
Concave-on-convex
- rolls and slides in the same direction
- can roll and slide around the convex surface
What are the characteristics of a close-packed position?
- position of max congruency
- most ligaments/capsules taut
- mechanically compressed (hard to seperate)
- stable
- generally near end range
- reduced need for muscle forces
- LE associated with habitual function
What are the characteristics of an open-packed position (loose-packed position)?
- joint surfaces incongruent
- ligaments/capsules most lax
- joint cavity has greatest volume
- usually least congruent near midrange
- LE biased toward flexion
- usually preferred during long periods of immobilization
Define force
- push or pull that can produce, arrest, or modify movement
- also called “load”
What is the stress-strain curve?
- this is a curve showing a muscle’s ability to lengthen until it reaches its failure point
What does stress mean in the stress-strain curve?
- the resistance of the tissue to the force that is being applied to the tissue
What does strain mean in the stress-strain curve?
- the percent increase in stretch to the tissue length relative to its original length
What does the “toe” region mean in the stress-strain curve?
- the initial wavy or crimped tissue that must become taut before tissue is measured
What does the elastic region mean in the stress-strain curve?
- the region where stress is being added to a tissue but length of tissue will return to normal after the force has been removed from the tissue
What does the yield point mean in the stress-strain curve?
- the tissue is elongated to a point where no stress/resistance occurs but continues to elongate
- strain continues but stress does not
- pulling laffy taffy apart to the point it is super stringy
What does the plastic region in the stress-strain curve mean?
- strain continues and microscopic failures begin to form
- tissue cannot return to normal and stays deformed
What is the ultimate failure point in the stress-strain curve?
- point when the tissue fails/tears
At what point do tendons usually fail at?
- fail at 8-13% beyond pre-stretch length
What does the rate of loading pertain to?
- for viscoelasticity properties
- faster you load something the more resistance it gives back
- protective mechanism AS LONG AS it is in elastic range
What is viscoelasticity?
- this is property of tissue
- it is elastic and viscous at the same time
- allows the tissue to return back to normal as long as still within the elastic region
What is creep?
- actual elongation of tissue when exposed to a constant load over time
What does “elastic” mean when it pertains to muscle deformation?
- muscles will return to normal length after stretch has finished
What does “plastic” mean when it pertains to muscle deformation?
- muscles will NOT return to normal length after stretch has finished
Explain Newtons first law of motion
Law of Inertia:
- Linear: body remains at rest or at constant linear velocity except when compelled by an external force
- hockey puck
- Angular: body remains at rest or at constant angular velocity around AoR unless compelled by external torque
- merry-go-round
Explain Newtons second law of motion
Law of Acceleration:
- Linear: DIRECTLY proportional to the force causing it and takes place in same direction as the force acts and is INVERSELY proportional to mass
- a=F/M
- Angular: DIRECTLY proportional to the torque causing it and takes place in same rotary direction as torque acts and is INVERSELY proportional to the mass moment of inertia of the body
- (a=T/I)
Explain Newtons third law of motion
Action-Reaction:
- Linear: for every force there is an equal and opposite directed force
-Angular: for every torque there is an equal and opposite directed torque
Define Center of Mass
- center of gravity
- hypothetical point at which all the mass of an object appears to be concentrated (balancing point)
What is the line of gravity
- LoG
- gravitational vector always vertically downward like a plumb line
What is the mass moment of inertia?
- an object’s resistance to rotary motion or change in rotary motion
What is inertia?
- the amount of energy required to alter the velocity of a body
- directly proportional to mass
- an object in motion will resist any increase, decrease, or change in motion
What are the different equations for speed, velocity, and acceleration?
Speed = distance/time
- no direction, scalar
Velocity = distance/time
- with direction, vector
Acceleration = change in velocity/time
- vector, linear angular
What would happen to an arms CoM and muscles if weight is added to the wrist?
CoM: would move toward the wrist due to the increased weight
Muscles: it would make the muscles work harder due to added weight and an increase in the moment arm
What is the relationship between CoM and Mass Moment of Inertia?
- CoM affects Mass Moment
- closer composite CoM is for each extremity (U + L) the faster velocity will be (this creates less resistance to wind)
- further away, the slower rotary velocity will be
How does the acceleration of an object change if the force to move it remains constant but the mass of the object decreases?
- acceleration will increase because the force remains constant while decreasing the weight being pulled
Would force need to increase or decrease from the quads when changing a 5 pound weight from knee Ext to lifting a 10 pound weight if movement speed stayed the same?
- force would need to increase
What is an internal force?
- produced from structures in the body
- active or passive
What is an external force?
- produced by forces acting from outside the body
- gravity or external load
What is joint reaction force (JRF) compared to ground reaction force (GRF)
Joint Reaction Force:
- joints pushing back against gravity and body weight
- caused in reaction to other forces
- muscle activation, passive tension in connective tissue
Ground Reaction Force:
- ground generates force in opposite direction but EQUAL in magnitude
What is a vector?
- a quantity with magnitude and direction
- shown using arrows
What characteristics apply to all force vectors?
- magnitude (size and length)
- direction (arrowhead pointing)
- spatial orientation (arrow shaft position)
- point of application (arrow base contacts segment)
- angle of insertion (angle formed between tendon and long axis of bone at insertion
How can a joint be in static linear equilibrium?
- when sum of forces = 0
- JRF + Internal + External forces = 0
- Forces equal each other
Define torque
- force in rotary direction
What orientation will produce the best torque?
- being perpendicular to the moment arm
How can a joint be in static rotary equilibrium?
- Internal torque + External torque = 0
Define a “moment arm”
- perpendicular distance between AoR and the force
What is an Internal moment arm (IMA)?
- from AoR to Internal force
What is an External moment arm (EMA)?
- from AoR to External force
What is Internal and External torque?
Internal Torque:
= Internal Force x IMA
External Torque:
= External force x EMA
What size moment arm creates the most leverage?
- a longer moment arm will create more leverage
- a shorter moment arm will create less leverage
How does moment arm affect the ability of a force to rotate a segment?
- this can determine leverage
- shorter a moment arm, the less leverage which means force isn’t as effective at producing
What is a force couple?
- when 2 or more muscles simultaneously produce forces in different linear directions BUT result in same rotary direction
Describe a first class lever
- AoR is b/w IMA & EMA
- seesaw
- mechanical advantage can be =, >, < 1
- cervical head nodding
Describe a second class lever
- EMA is b/w AoR & IMA
- wheel barrows
- Mechanical advantage always > 1
- gastrocnemius & soleus plantar flexion
Describe a third class lever
- IMA + IF is b/w AoR & EF + EMA
- mechanical advantage always < 1
- deltoids
Which system allows for a greater arc of motion or angular displacement?
- 3rd class will allow a greater arc of motion
- because IMA is closer to the AoR allowing for more motion & angular displacement
What factors can cause the net torque on a segment to change?
- length of EMA
- Force of EF
- Force of IF
