1. Segmental Power Analysis
D. Gordon E. Robertson, PhD, FCSB
School of Human Kinetics
University of Ottawa

2. 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.
9/21/2018
Biomechanics Lab, University of Ottaw

3. Biomechanics Lab, University of Ottaw
Solve for forces & moments of foot
9/21/2018
Biomechanics Lab, University of Ottaw

4. Biomechanics Lab, University of Ottaw
Continue with leg & thigh etc.
9/21/2018
Biomechanics Lab, University of Ottaw

5. 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
9/21/2018
Biomechanics Lab, University of Ottaw

6. Power Sources of a 4-segment 2D Model of the Human
9/21/2018
Biomechanics Lab, University of Ottaw

7. Segmental Power Analysis
Draw stick figure of body based on absolute angles of each segment
9/21/2018
Biomechanics Lab, University of Ottaw

8. Segmental Power Analysis
Draw force powers as straight arrows through the joint in the direction of the energy transfer
9/21/2018
Biomechanics Lab, University of Ottaw

9. 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
9/21/2018
Biomechanics Lab, University of Ottaw

10. Segmental Power Analysis
Draw moment powers as curved arrows around joint on same side as the moment of force (flexor vs. extensor)
9/21/2018
Biomechanics Lab, University of Ottaw

11. 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
9/21/2018
Biomechanics Lab, University of Ottaw

12. Biomechanics Lab, University of Ottaw
Example
Start with the stick figure
9/21/2018
Biomechanics Lab, University of Ottaw

13. Biomechanics Lab, University of Ottaw
Next add Ankle Powers
Ankle force transfers energy from foot to leg
Ankle moment transfers energy from foot to leg
9/21/2018
Biomechanics Lab, University of Ottaw

14. Biomechanics Lab, University of Ottaw
Next add Knee Powers
Knee force transfers energy to thigh from leg
Knee flexor moment generates energy to leg and thigh
Knee flexor moment generates energy to leg
9/21/2018
Biomechanics Lab, University of Ottaw

15. Biomechanics Lab, University of Ottaw
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
9/21/2018
Biomechanics Lab, University of Ottaw