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.
