Lecture 2: Definitions Flashcards
Biomechanics
application of physics to the understanding of the motions and deformations of body segments, organs, structures, tissues, cells due to forces, pressures, torques, shears, etc
Linked rigid body biomechanics
Rigid bodies are linked at joints
- bones are rigid and muscles deform
Rigid body
mass with a volume
assumption that segments btwn links are rigid = not actually rigid
Advantages/disadvantages for X-Rays with biomecahnics
no error w/ soft tissue motion
drawbacks: exposure to ionizing radiation
- have to time amount of exposure
Skeletal biomechanics
Deformation of the FACIAL SKELETON after getting hit in the face
- facial skeleton deforms a lot (everyday when chewing)
Facial fractures
heal well b/c face is highly vascularized
Vascular biomechanics
Modeling BOTH the DEFORMATION of the wall of a blood vessel and the BLOOD FLOW within the vessel
Cellular biomechanics
Measuring the FORCES with which cells interact w/ their surroundings
Cells can bear and exert force
Assumptions with linked rigid body biomechanics
- Body segments are RIGID
- Segments connect at JOINTS
- Joints have a well-defined number of ‘DEGREES OF FREEDOM’
Degrees of freedom
6 total degrees of freedom (3 linear + 3 rotational)
If there are 6 degrees, 2 rigid bodies are NOT attached
- need to constrain at least one degree of freedom to be attached
Max degrees of freedom is needed for a joint?
Maximum is 5 degrees b/c at least one has to be constrained
Example of joint with 5 degrees of freedom
Temporal mandibular jaw (btwn face and jawline)
- 3 rotational and 2 linear
Degrees of freedom: Hip
Hip has 3 degrees of ROTATIONAL freedom (flex/extend, adduct/abduct, internal/external rotation)
NO linear degrees of freedom
Degrees of freedom: Knee
Knee is a hinge jt. = 1 degree of freedom (ONLY flexion/extension)
doesn’t move in any other degrees (constrained by bony congruents or ligaments)
- linear degrees constrained by ACL/PCL
Applications of linked rigid body mechanics
- coaching
- rehab
- orthopaedic
- ergonomics in workplace
- clothing/fashion
- animation (CGI)
Anthropometrics
Measurements of physical characteristics of the human body
- height and weight (easy to measure)
- body segment lengths, weights, volumes, shapes (uses cadavers)
- location of centre of mass
- moments of inertia
Moments of inertia
Bigger moment of inertia = harder to rotate
Smaller moment of inertia = easier to rotate
Mechanics
Physics of forces and motion
2 categories: statics and dynamics
Statics
the study of bodies WITHOUT acceleration
NO inertia
- not necessarily still/at rest
Dynamics
the study of bodies WITH acceleration
Correct way to analyze biomechanics but trickier
Acceleration
Linear motion
Time rate of change of velocity (2nd derivative of position)
Need to apply a FORCE
measured in m/s^2
Velocity
Linear motion
Time rate of change of position (1st derivative of position)
measured in m/s
Position
Linear motion
in meters (m)
Angular acceleration
Time rate of change of angular velocity
in degrees/s^2
Linear and rotational motion relationship
Linear and rotational motion are INDEPENDENT of each other
But both are present
Kinematics
Study of GEOMETRY of motion
Position, velocity, acceleration
Angle, angular velocity, angular acceleration
Kinetics
studies CAUSES of motion
Force, pressure, torque, tension, shear, compression
Inverse kinetics/dynamics
Measure KINEMATICS FIRST then work ‘backwords’ to figure out kinetics that must have caused motion
EASIER TO DO IN LAB
Forward kinetics/dynamics
Measure KINETICS FIRST then try to figure out where the body is going to go
- really hard to do in lab
- how you learned to work
