Segmental Power Analysis

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Segmental Power Analysis

• D. Gordon E. Robertson, PhD, FCSB
• School of Human Kinetics
• University of Ottawa

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Inverse DynamicsComputes 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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• Solve for forces moments of foot

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• Continue with leg thigh etc.

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Next Compute PowersJoint 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
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Segmental Power Analysis

• Draw stick figure of body based on absolute
  angles of each segment

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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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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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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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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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Example

• Start with the stick figure

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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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Next add Knee Powers

• Knee force transfers energy to thigh from leg

• Knee flexor moment generates energy to leg

• Knee flexor moment generates energy to leg and
  thigh

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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