Foundations of Biomechanics II: The Sequel Flashcards
1
Q
Intro to Kinematic Analysis
A
- deals with description of spatial and temporal components of motion
- no concern for force production
- may be either qualitative or quantitative
2
Q
Linear Kinematic Analysis
A
- describes linear or translational motion
- may collect data in many ways: accelerometers, high speed cinematography, electromagnetic sensors
- digitization allows for conversion of data
3
Q
Coordinate Reference Systems
A
- absolute reference systems used to “make sense” of it all
- either 2D or 3D
- cartesian or rectangular reference system used for remainder of this course
- values expressed as x, y, and z
4
Q
Collecting Data on Variables of Interest
A
- markers or sensors typically placed on body
- placed on prior to movement
- to analyze: biomechanist or clinician measures landmarks, one frame at a time
- coordinate system remains constant: grid doesn’t move the marker does
- each landmark thus referenced to x-y axes for each moment in time
5
Q
Measuring Relationship of Movement and Time
A
- time aka temporal factors
- basic interest of kinematic analysis
- examples include: cadence, stride duration, stance or support phase, swing phase
- knowledge of temporal factors is often “key” clinically: gait velocity, symmetry of gait
- movement occurs secondary to change in position over time
6
Q
Units of Measure
A
- SI or metric system used exclusively: in scientific research, in clinical journals
- base measures are mass, length, time, temperature
- other units derived from these base units
7
Q
Position and Displacement
A
- position refers to object’s location in space
- relative to some reference point
- motion occurs when object or body changes position
- displacement is measured in straight line, from one point to another
- distance may or may not be a straight line: scalar quantity
- displacement is not to be confused with distance: vectors used to measure displacement
8
Q
Speed and Velocity
A
- speed is scalar: lay term, widely used
- velocity combines concepts of displacement and time
- velocity is a vector quantity
9
Q
Velocity and Speed
A
- may be expressed as instantaneous or average
- velocity is typically of more interest clinically than is speed
10
Q
Acceleration
A
- velocity is rarely constant in human motion
- distance runner in race
- with each ground contact
- transfers
- acceleration describes change in velocity with respect to time
11
Q
Deceleration
A
- most injury happens here
- eccentric contraction happens trying to keep stabilized and get stretched then you can tear it-more susceptible to injury when muscle is longer
- forces on body are highest compared to isometric or concentric–>issue makes them vulnerable during deceleration
12
Q
Using Linear Kinematics: Analyzing Running
A
- cyclic, sequential form of motion
- among most basic of motions studied
- locomotor cycle defined by events in sequence
- step describes events occurring between contacts of opposite feet
- stride describes events occurring between contact of same foot
- among most studied parameters: stride length and rate
- stride length: displacement covered by one stride
- stride rate: number of strides per minute
13
Q
Using Linear Kinematics: Running Velocity
A
- running velocity is product of stride rate and stride length
- runners can increase velocity by: increasing stride length, rate, or both
- studies show that runners: initially increase stride length then later increase stride rate
- physical limit to how much one can increase stride length
- most efficient runners rely more so on increased stride rate to increase velocity
- support phase: foot in contact with ground, from impact to foot leaving ground
- swing phase: foot off ground, from foot leaving ground to contact
- support time decreases as running velocity increases
- relative support times: jogging 68%, running 54%, sprinting 47%
14
Q
Using Linear Kinematics: Acceleration in Running
A
- one cannot accelerate indefinitely (AV Hill)
- runner’s velocity 0 at start
- accelerates rapidly at first
- but acceleration eventually decreases
- best sprinters actually lose less velocity
- horizontal velocity changes constantly during running
- distinct negative and positive accelerations exist in every gait cycle
- horizontal velocity slows each time the foot hits the ground
- horizontal velocity continues to slow during 1st portion of support phase
- “over striding” leads to greater deceleration with each foot contact
- over striding increases metabolic energy needed to maintain given horizontal velocity: deceleration force means energy needs to increase
- over striding increases the force absorbed by the musculoskeletal system with each step
- metabolic needs increase for people who spend more time on the ground
15
Q
Angular Kinematic Analysis
A
- angular motion occurs with many body movements
- linked to rotary motion: joint motion typically occurs about an axis
- body parts move through same angle but do not undergo same linear displacement
16
Q
Angular Kinematics
A
- understanding rotation is critical to comprehending human movement
- nearly all motion involves rotations of body segments
17
Q
Measurement of Angles
A
- angle composed of 2 intersecting lines
- lines join at vertex
- in biomechanical analysis: vertex is typically within joint, lines generally body segments
18
Q
Instantaneous Joint Center
A
- using goniometer or placing joint markers makes technically incorrect assumption
- one or both bones comprising joint may displace relative to one another
- thus joint center actually changes during motion
- instantaneous joint center is center of rotation of joint at a given instant
19
Q
Units of Angular Motion
A
- 3 used to measure joint motion
- degree is most common method
- revolution is another method
- radian measures: angle at center of circle
- circle described by an arc equal to the length of the radius of the circle
- radians is dimensionless as both s and r measured in meters, numerator and denominator cancel out
20
Q
Relative Angle
A
- defines the included angle between longitudinal axes of 2 segments
- ex: relative angle at elbow, knee, etc
- does not describe position of segment, sides of angle in space
21
Q
Absolute Angle
A
- defines angle of inclination of body segment
- describes orientation of a segment in space
- uses universal or absolute reference system
- calculated via 2 primary ways: placing coordinate system at proximal endpoint of segment or placing coordinate system at distal endpoint of segment (more common)
- angle then measured in CCW direction from right horizontal
- convention used must be stated clearly in manuscript
22
Q
Angular Motion
A
- relationships discussed on linear kinematics comparable to angular case
- angular case is simply analog of linear case: velocity, acceleration
23
Q
Angular Distance and Displacement
A
- distance: total of all angular changes, measured following exact path
- displacement: difference between initial and final positions
24
Q
Angular Speed
A
- angular distance traveled per unit time
- angular speed=angular distance/time
- scalar
- not really clinically or biomechanically relevant
25
Q
Angular Velocity
A
- a vector quantity
- describes time rate of change of angular position
26
Q
Calculating Angular Velocity
A
- isokinetic muscle testing
- use formula
27
Q
Angular Acceleration
A
- describes rate of change of angular velocity per unit time
- ex: elbow flexion-motion is only 1 direction but has both + and - angular accelerations
28
Q
Relationship Between Angular and Linear Motion
A
- many human movements arising from angular motion result in linear motion: walking, biking, pitching, throwing frisbee, golfing
- linear motion often results from the sum of the given angular velocity or velocities
29
Q
Linear and Angular Displacement
A
-linear displacement is a product of radius of rotation and angular displacement
30
Q
Linear and Angular Velocity
A
- linear velocity vector is instantaneously tangent to path of object
- aka tangential velocity
- tector is perpendicular to rotating segment
31
Q
Applying Kinematics in Clinic
A
- more common to film patients allows for higher level movement analysis
- velocity of patient’s center of mass during gait cycle: increases and decreases with each step
- increasing or decreasing gait speed often depends on increasing or increasing angular velocity
- bigger wheels which have a larger angular velocity often make it easier for some patients to make the transition from solid flooring to carpet, to turn
- this type of relationship is often manipulated in prosthetic knee in order to betternormalize gait
32
Q
Take Home Points
A
- rectangular reference system provides basis for 2D and 3D kinematic assessment of human motion
- numerous applications of linear and angular motion exist in human movement
- kinematic measures such as position, displacement, velocity, and acceleration allow movement professionals to precisely describe what they see
