Foundations of Biomechanics II: The Sequel Flashcards Preview

DPT 726: Orthopaedic Foundations > Foundations of Biomechanics II: The Sequel > Flashcards

Flashcards in Foundations of Biomechanics II: The Sequel Deck (32)
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Intro to Kinematic Analysis

-deals with description of spatial and temporal components of motion
-no concern for force production
-may be either qualitative or quantitative


Linear Kinematic Analysis

-describes linear or translational motion
-may collect data in many ways: accelerometers, high speed cinematography, electromagnetic sensors
-digitization allows for conversion of data


Coordinate Reference Systems

-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


Collecting Data on Variables of Interest

-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


Measuring Relationship of Movement and Time

-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


Units of Measure

-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


Position and Displacement

-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


Speed and Velocity

-speed is scalar: lay term, widely used
-velocity combines concepts of displacement and time
-velocity is a vector quantity


Velocity and Speed

-may be expressed as instantaneous or average
-velocity is typically of more interest clinically than is speed



-velocity is rarely constant in human motion
-distance runner in race
-with each ground contact
-acceleration describes change in velocity with respect to time



-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


Using Linear Kinematics: Analyzing Running

-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


Using Linear Kinematics: Running Velocity

-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%


Using Linear Kinematics: Acceleration in Running

-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


Angular Kinematic Analysis

-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


Angular Kinematics

-understanding rotation is critical to comprehending human movement
-nearly all motion involves rotations of body segments


Measurement of Angles

-angle composed of 2 intersecting lines
-lines join at vertex
-in biomechanical analysis: vertex is typically within joint, lines generally body segments


Instantaneous Joint Center

-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


Units of Angular Motion

-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


Relative Angle

-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


Absolute Angle

-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


Angular Motion

-relationships discussed on linear kinematics comparable to angular case
-angular case is simply analog of linear case: velocity, acceleration


Angular Distance and Displacement

-distance: total of all angular changes, measured following exact path
-displacement: difference between initial and final positions


Angular Speed

-angular distance traveled per unit time
-angular speed=angular distance/time
-not really clinically or biomechanically relevant


Angular Velocity

-a vector quantity
-describes time rate of change of angular position


Calculating Angular Velocity

-isokinetic muscle testing
-use formula


Angular Acceleration

-describes rate of change of angular velocity per unit time
-ex: elbow flexion-motion is only 1 direction but has both + and - angular accelerations


Relationship Between Angular and Linear Motion

-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


Linear and Angular Displacement

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


Linear and Angular Velocity

-linear velocity vector is instantaneously tangent to path of object
-aka tangential velocity
-tector is perpendicular to rotating segment