Inverse Dynamics D. Gordon E. Robertson, PhD, FCSB School of Human Kinetics University of Ottawa.
Kinetics versus Kinematics for Analyzing Locomotor Coordination D. Gordon E. Robertson, Ph.D. School...
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Transcript of Kinetics versus Kinematics for Analyzing Locomotor Coordination D. Gordon E. Robertson, Ph.D. School...
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.
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300.
-20.
0.
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P
ow
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Mom
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t (N
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A
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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.
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P
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Mom
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vel.
(/s
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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.
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-20.
0.
20.
P
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(W)
M
om
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vel.
(/s
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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
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(W)
Mom
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.m)
A
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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
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(W)
M
om
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t (N
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A
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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
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(W)
M
om
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t (N
.m)
A
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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.
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10.
P
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M
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r vel.
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)
Trial: WN02DRMP
IFS CTO CFS ITO IFS
Flexing
Extending
Flexor
Extensor
Concentric
Eccentric