Flashcards in Foundations of Biomechanics II: The Sequel Deck (32)

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1

## Intro to Kinematic Analysis

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-deals with description of spatial and temporal components of motion

-no concern for force production

-may be either qualitative or quantitative

2

## Linear Kinematic Analysis

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-describes linear or translational motion

-may collect data in many ways: accelerometers, high speed cinematography, electromagnetic sensors

-digitization allows for conversion of data

3

## Coordinate Reference Systems

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-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

## Collecting Data on Variables of Interest

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-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

## Measuring Relationship of Movement and Time

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-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

## Units of Measure

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-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

## Position and Displacement

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-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

## Speed and Velocity

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-speed is scalar: lay term, widely used

-velocity combines concepts of displacement and time

-velocity is a vector quantity

9

## Velocity and Speed

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-may be expressed as instantaneous or average

-velocity is typically of more interest clinically than is speed

10

## Acceleration

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-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

## Deceleration

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-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

## Using Linear Kinematics: Analyzing Running

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-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

## Using Linear Kinematics: Running Velocity

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-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

## Using Linear Kinematics: Acceleration in Running

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-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

## Angular Kinematic Analysis

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-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

## Angular Kinematics

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-understanding rotation is critical to comprehending human movement

-nearly all motion involves rotations of body segments

17

## Measurement of Angles

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-angle composed of 2 intersecting lines

-lines join at vertex

-in biomechanical analysis: vertex is typically within joint, lines generally body segments

18

## Instantaneous Joint Center

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-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

## Units of Angular Motion

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-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

## Relative Angle

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-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

## Absolute Angle

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-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

## Angular Motion

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-relationships discussed on linear kinematics comparable to angular case

-angular case is simply analog of linear case: velocity, acceleration

23

## Angular Distance and Displacement

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-distance: total of all angular changes, measured following exact path

-displacement: difference between initial and final positions

24

## Angular Speed

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-angular distance traveled per unit time

-angular speed=angular distance/time

-scalar

-not really clinically or biomechanically relevant

25

## Angular Velocity

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-a vector quantity

-describes time rate of change of angular position

26

## Calculating Angular Velocity

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-isokinetic muscle testing

-use formula

27

## Angular Acceleration

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-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

## Relationship Between Angular and Linear Motion

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-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

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## Linear and Angular Displacement

### -linear displacement is a product of radius of rotation and angular displacement

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