Kinetics versus Kinematics for Analyzing Locomotor

Coordination

D. Gordon E. Robertson, Ph.D.

School of Human Kinetics,

University of Ottawa, Ottawa, CANADA

Kinematic Analysis

• linear position, velocity and acceleration of markers

• linear position, velocity and acceleration of body segments

• angular position, velocity and acceleration of body segments

• total body or limb kinematics

Advantages of Kinematics

• easy to obtain with automated motion analysis systems

• accuracy is easy to determine

• requires little operator expertise

• immediate feedback possible

Disadvantages of Kinematics

• only describes motion

• not indicative of causes

• difficult to discriminate important variables from idiosyncratic variables

Kinetic Analysis

• forces and moments of force

• work, energy and power

• impulse and momentum

• inverse dynamics derives forces and moments from kinematics and body segment parameters

Advantages of Kinetics

• defines which structures cause the motion (i.e., coordination)

• can be used to simulate motion and describe resulting kinematics

• can be validated against external force measurements

Disadvantages of Kinetics

• may require synchronization of several data acquisition systems (e.g., videography with force plates)

• special training to interpret

• more expensive and less developed software

• invasive for direct internal measurements (muscle, ligament, or bone forces)

Inverse Dynamics is Partial Solution to Invasive Measurements

• noninvasive with videography

• kinematics are determined

• direct measurements of external forces are often necessary (i.e., force platforms)

• can be applied at several joints, simultaneously

Limitations of Inverse Dynamics

• results apply to conceptual structures not true anatomical structures

• cannot partition results into contributions by individual anatomical structures

• no direct means of validating

• modeling permits partitioning of forces and moments

Sprint Analysis Example

• swing phase of one leg

• world-class male sprinter

• 50 m into 100 m competitive race (t=10.06 s)

• analysis of hip and knee only (ankle forces not significant during swing)

Hip angular velocity, moment of force and power during sprinting

• initial burst of power to create swing

• latter burst to drive leg down

0.0 0.1 0.2 0.3 0.4Time (s)

-4000.

-2000.

0.

2000.

-300.

0.

300.

-20.

0.

20.

P

ow

er

(W)

Mom

en

t (N

.m)

A

ng

ula

r vel.

(/s

)

Toe-off Touch-down

Extending

Flexing

Extensor

Flexor

Concentric

Eccentric

Hip Moment

• causes rapid hip and knee flexion immediately after toe-off

• causes hip and knee to extend in preparation for touch-down

Knee angular velocity, moment of force and power during sprinting

• initial burst of power to stop flexion

• small burst for extension

• final burst to stop extension

0.0 0.1 0.2 0.3 0.4Time (s)

-4000.

-2000.

0.

2000.

-300.

0.

300.

-20.

0.

20.

P

ow

er

(W)

Mom

en

t (N

.m)

An

gu

lar

vel.

(/s

)

Toe-off Touch-down

Extending

Flexing

Extensor

Flexor

Concentric

Eccentric

Knee Moment

• not used to cause flexion or extension during swing

• stops knee flexion before mid-swing

• prevents hyper-extension (locking) prior to touch-down

Hip angular velocity, moment of force and power during kicking

• initial burst of power to create swing

• negative work to create whip-action of leg and foot 0.0 0.1 0.2 0.3

Time (s)

-2000.

-1000.

0.

1000.

-200.

0.

200.

-20.

0.

20.

P

ow

er

(W)

M

om

en

t (N

.m)

An

gu

lar

vel.

(/s

)

Trial: SL2CF

CFS Hit Off

Flexing

Extending

Flexor

Extensor

Concentric

Eccentric

Knee angular velocity, moment of force and power during kicking

• initial power to stop flexion, bumper effect

• negative power prior to contact to prevent hyperextension

0.0 0.1 0.2 0.3

Time (s)

-2000.

-1000.

0.

1000.

-200.

0.

200.

-20.

0.

20.

P

ow

er

(W)

Mom

en

t (N

.m)

A

ng

ula

r vel.

(/s

)

Trial: SL2CF

CFS Hit Off

Extending

Flexing

Extensor

Flexor

Concentric

Eccentric

Normal Walking Example

• athletic male subject

• laboratory setting

• speed was 1.75 m/s

• IFS=ipsilateral foot-strike

• ITO=ipsilateral toe-off

• CFS=contralateral foot-strike

• CTO=contralateral toe-off

Ankle angular velocity, moment of force and power during walking

• large burst of power by plantar flexors for push-off

• dorsiflexors allow gentle landing and flexion during swing 0.0 0.2 0.4 0.6 0.8 1.0

Time (s)

-750.

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

P

ow

er

(W)

M

om

en

t (N

.m)

A

ng

ula

r vel.

(/s

)

Trial: WN02DRMP

IFS CTO CFS ITO IFS

Dorsiflexing

Plantar flexing

Dorsiflexor

Plantar flexor

Concentric

Eccentric

Knee angular velocity, moment of force and power during walking

• initial burst of power to cushion landing

• positive work to extend knee

• negative work by extensors to control flexion at push-off

0.0 0.2 0.4 0.6 0.8 1.0Time (s)

-750.

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

P

ow

er

(W)

M

om

en

t (N

.m)

A

ng

ula

r vel.

(/s

)

Trial: WN02DRMP

IFS CTO CFS ITO IFS

Extending

Flexing

Extensor

Flexor

Concentric

Eccentric

Hip angular velocity, moment of force and power during walking

• some cushioning at landing

• large amount of negative work by flexors

• positive work by flexors to swing leg

0.0 0.2 0.4 0.6 0.8 1.0Time (s)

-750.

-500.

-250.

0.

250.

-100.

0.

100.

-10.

0.

10.

P

ow

er

(W)

M

om

en

t (N

.m)

A

ng

ula

r vel.

(/s

)

Trial: WN02DRMP

IFS CTO CFS ITO IFS

Flexing

Extending

Flexor

Extensor

Concentric

Eccentric

Questions?

Answers?

Thank you.