Overview + Kinematics

Biomechanics

study of the forces which act on living tissues (bodies) and the effects of these forces

kinesiology

science or the study of movement → does not take forces that cause the movement into account

kinematics includes descriptors of:

• type of motion

• direction of motion

• quantity of motion

• quality of motion

segment

considered to be an individual part of the body between two points of mobility or joints

application of segments

the upper arm, forearm, and hand are all segments of the upper extremity

system

combination of segments

application of a system

arms, legs, the entire body

planes

surface on which the movement occurs or takes place

• 2-dimensional

• sagittal, frontal (coronal), transverse (horizontal)

axes

a straight line about which the movement occurs or a body, segment, or object rotates

• movement occurs around an axis that is perpendicular to the plane of movement

• frontal (medio-lateral), sagittal (antero-posterior), longitudinal (vertical)

planes and axes: sagittal plane

sagittal plane → frontal/coronal axis

planes and axes: frontal plane

frontal plane → sagittal axis

planes and axes: transverse plane

transverse plane → longitudinal axis

sagittal plane/frontal axis motions

flexion and extension

flexion: biomechanical definition

narrowing of angle between segments

extension: biomechanical definition

increasing the angle between segments

reference of movements

always reference the distal end → abducting your arm, your hand is the distal segment and that is abducting

rotary movements

angular, rotation

translation/translatory movement

linear → moves in a straight line

curvilinear

angular and linear

osteokinematics

movement of segments/system (bones) in one or more planes

• movement that is VISIBLE

• rotatory/rotary/rotation

arthro

= joints

arthrokinematics

motion at the joint level that is NOT readily visible in 3 forms:

1. rolling

2. gliding

3. spinning

rolling - arthrokinematics

different parts touch the ground at different times

• curvilinear

gliding - arthrokinematics

also called sliding

• translation/translatory/linear

• same point touches the ground the whole time

spinning

rotatory/rotary/rotation

• stays in the same place

degrees of freedom (DOF)

number of independent movements allowed at a joint

• can be rotations or translations

• helps to determine the actual movement that occurs within the joint

relationship between axis and joint center of rotation

• instantaneous center of joint rotation moves as the joint moves → doesn’t stay in one spot

• position of axis at one movement in time

• goniometry/2D vs 3D motion capture

normal osteokinematic motion

combination of angular movement of bone around its joint center of rotation with arthrokinematic movements of joint surfaces within the available degrees of freedom the joint allows

arthrokinematics and joint axis

• poor movement patterns/poor motor control may occur if normal arthrokinematic movement does not occur

convex-concave principles

• relationship between articular surfaces and movement of bone

• convex-concave principles will be addressed in relationship to the normal arthrokinematics of an otherwise healthy joint

• convex-concave principles should NOT take the place of your exam and impairments found in joint accessory motion as a result of your exam

convex on concave

• glide is in opposite direction of bone movement

• ex) humerus head glides up in the GHJ, the hand (distal segment) is moving down

concave on convex

glide is in the same direction as movement of the bone

qualitative kinematics

HOW → observing body, segment, and joint behavior to aid in examinations

• planes

• axes

• movements

• joints

• osteokinematics/arthrokinematics

quantitative kinematics

HOW MUCH → understanding and being able to implement best practice related to biomechanics

• goniometry

• gait speed

position

location of a point or object in space

scalar

magnitude only (single number)

• ex) time, length

vectors

magnitude, direction, point of application, orientation

• ex) velocity, force

vectors terms

• magnitude: length of the line

• direction: which way is the arrowhead pointed

• point of application: where the tail attaches

• orientation: vertical/horizontal, other angles

distance

total length without regard to direction (scalar)

• ex) walk 2m and turn around following the same path back to the beginning spot → total distance = 2m + 2m = 4m

displacement

directional dependent (vector quantity)

• ex) walk 2 m and turn around following the same path to the beginning spot → total displacement = 2m + -2m = 0m

linear displacement

△d = d₂ - d₁

△d = d_i+1 - d_i

units = mm/cm/m, in/ft/miles, etc

angular displacement

△θ = θ₂ - θ₁

△θ = θ_i+1 - θ_i

units = degrees, radians

speed

• change in distance over time

• scalar looking only at magnitude

• also describes qualitative observations → slow/fast

• tends to be used interchangeably with average velocity

velocity

• change in displacement over time

• vector quantity so orientation and direction are important

average velocity

examines changes in 2 positions (A to B) over the time it took to get from A to B

instantaneous velocity

as the time interval becomes smaller and smaller (approaching zero), use differential of position related to time (calculus)

linear velocity

△d/△t → v = (d₂ - d₁)/(t₂ - t₁)

units = cm/s or m/s

angular velocity

ω = △θ/△t → ω = (θ₂ - θ₁) / (t₂ - t₁)

units = degree/s or rad/s

acceleration

time derivative of velocity → changes in velocity over time

• may have average acceleration over an interval or instantaneous acceleration (time approaching zero)

linear acceleration

a = △v/△t → a = (v₂ - v₁)/(t₂ - t₁)

units = cm/s² or m/s²

angular acceleration

α = △ω/△t → α = (ω₂ - ω₁)/(t₂ - t₁)

units = degrees/s² or rad/s²

deceleration

technically → no such thing as deceleration or a negative acceleration

• deceleration implies a negatively directed acceleration, not just a change in the acceleration or a change in direction on a graph

• in certain contexts, slowing down or coming to a stop may be abrupt

• deceleration injuries or deceleration trauma is a general classification to indicate that an individual was moving and then wasn’t moving type of collision

deceleration injuries

• implications for concussion

• implications for non-contact injury like ACL tear

frames of reference

• component/cartesian coordinate system

• mostly 2D

• orthogonal system for 3D

frames of reference: right hand rule

counterclockwise (CCW) → indicated by +

clockwise (CW) → indicated by -