Transcript Segmental Power Analysis

Segmental Power
Analysis
D. Gordon E. Robertson, PhD, FCSB
School of Human Kinetics
University of Ottawa
Inverse Dynamics
Computes Net Forces and Moments at each Joint
 Net force represents the sum of all the
structures that can create forces across
the joint. It does not include gravitational
or ground reaction forces.
 Net moments of force are the sum of all
the structures that create moments by
acting across the joint. In general,
muscles are the principal causes of these
moments.
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Biomechanics Lab, University of
Ottaw
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 Solve for forces
& moments of
foot
Mankle k
Fankle
Fground
mfoot g j
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Mknee k
Fknee
 Continue
with leg &
thigh etc.
–Fankle
–Mankle k
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Biomechanics Lab, University of
Ottaw
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Next Compute Powers
Joint Force Powers and Joint Moment Powers
 Force power is dot product of net force
(F) and linear velocity (v) of the joint
 F.v = FX vX + FY vY + FZ vZ
 Moment power is product of net moment
of force (M) and angular velocity of
segment (w)
 MX wX + MY wY + MZ wZ
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Power Sources of a 4-segment
2D Model of the Human
Segment
Ankle
Knee
Hip
= Total
1: Foot
+ F1 v 1 + M1 w1
= E1 /t
2: Leg
– F1 v 1 – M1 w2 + F2 v2 + M2 w2
= E2 /t
3: Thigh
– F2 v 2 – M2 w3 + F3 v3 + M3 w3 = E3 /t
4: Trunk
– F3 v 3 – M3 w4 = E4 /t
Ext. work
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M1 (w1 – w2)
+ M2 (w2 – w3)
+ M3 (w3 – w4)
Biomechanics Lab, University of
Ottaw
= ET /t
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Segmental Power Analysis
 Draw stick figure of
body based on
absolute angles of
each segment
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Biomechanics Lab, University of
Ottaw
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Segmental Power Analysis
 Draw force powers as
straight arrows through
the joint in the direction of
the energy transfer
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Biomechanics Lab, University of
Ottaw
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Segmental Power Analysis
 Draw force powers as
straight arrows through
the joint in the direction of
the energy transfer
 Use thicker lines for larger
powers
 Force powers are the
rates of transfer of energy
from one segment to
another
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Biomechanics Lab, University of
Ottaw
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Segmental Power Analysis
 Draw moment powers as
curved arrows around
joint on same side as the
moment of force (flexor
vs. extensor)
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Biomechanics Lab, University of
Ottaw
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Segmental Power Analysis
 Draw moment powers as
curved arrows around
joint on same side as the
moment of force (flexor
vs. extensor)
 Use thicker lines for larger
powers
 Moment powers show
generation, dissipation or
transfers of energy
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Ottaw
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Example
 Start with the stick figure
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Ottaw
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Next add Ankle Powers
 Ankle force transfers
energy from foot to
leg
 Ankle moment transfers
energy from foot to leg
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Biomechanics Lab, University of
Ottaw
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Next add Knee Powers
 Knee force transfers
energy to thigh from
leg
 Knee flexor moment
generates energy to leg
and thigh
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Biomechanics Lab, University of
Ottaw
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Next add Hip Powers
 Hip force transfers
energy to thigh from
trunk
 Knee flexor moment
generates energy to leg
 Hip flexor moment
 dissipates energy from
thigh
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Biomechanics Lab, University of
Ottaw
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