Foundations of Biomechanics II: The Sequel

Question 1

Intro to Kinematic Analysis

Answer 1

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

Question 2

Linear Kinematic Analysis

Answer 2

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

Question 3

Coordinate Reference Systems

Answer 3

• 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

Question 4

Collecting Data on Variables of Interest

Answer 4

• 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

Question 5

Measuring Relationship of Movement and Time

Answer 5

• 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

Question 6

Units of Measure

Answer 6

• 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

Question 7

Position and Displacement

Answer 7

• 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

Question 8

Speed and Velocity

Answer 8

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

Question 9

Velocity and Speed

Answer 9

• may be expressed as instantaneous or average

- velocity is typically of more interest clinically than is speed

Question 10

Acceleration

Answer 10

• 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

Question 11

Deceleration

Answer 11

• 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

Question 12

Using Linear Kinematics: Analyzing Running

Answer 12

• 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

Question 13

Using Linear Kinematics: Running Velocity

Answer 13

• 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%

Question 14

Using Linear Kinematics: Acceleration in Running

Answer 14

• 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

Question 15

Angular Kinematic Analysis

Answer 15

• 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

Question 16

Angular Kinematics

Answer 16

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

Question 17

Measurement of Angles

Answer 17

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

Question 18

Instantaneous Joint Center

Answer 18

• 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

Question 19

Units of Angular Motion

Answer 19

• 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

Question 20

Relative Angle

Answer 20

• 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

Question 21

Absolute Angle

Answer 21

• 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

Question 22

Angular Motion

Answer 22

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

Question 23

Angular Distance and Displacement

Answer 23

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

Question 24

Angular Speed

Answer 24

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

Question 25

Angular Velocity

Answer 25

• a vector quantity

- describes time rate of change of angular position

Question 26

Calculating Angular Velocity

Answer 26

• isokinetic muscle testing

- use formula

Question 27

Angular Acceleration

Answer 27

• describes rate of change of angular velocity per unit time

- ex: elbow flexion-motion is only 1 direction but has both + and - angular accelerations

Question 28

Relationship Between Angular and Linear Motion

Answer 28

• 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

Question 29

Linear and Angular Displacement

Answer 29

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

Question 30

Linear and Angular Velocity

Answer 30

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

Question 31

Applying Kinematics in Clinic

Answer 31

• 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

Question 32

Take Home Points

Answer 32

• 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