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Musculoskeletal Modeling

Musculoskeletal Modeling. Colin Smith. A method for Studying Movemen t. Things we can measure in movement: Kinematics (using motion capture) Output Forces (Using Force Plates) Muscle Activation Timing (EMG) What about in vivo? We need a model Muscle Forces Bone contact forces.

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Musculoskeletal Modeling

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  1. Musculoskeletal Modeling Colin Smith

  2. A method for Studying Movement • Things we can measure in movement: • Kinematics (using motion capture) • Output Forces (Using Force Plates) • Muscle Activation Timing (EMG) • What about in vivo? We need a model • Muscle Forces • Bone contact forces

  3. Musculoskeletal Models • Approach the body like a Machine • Model Bones as Rigid Bodies • Model Muscles as actuators

  4. Inverse Kinematics • Collect Motion Data • Scale Model to match subject • Use least squares method to match position of markers to model segments • We now know the kinematics of each body segment

  5. Inverse Kinetics • Solving the Equations of motion for each segment, we can find the forces and moments between each segment

  6. Muscle Forces • If we know the moments at a joint, we can find the muscle forces needed to create that moment • Distribution Problem • Multiple Muscles cross each joint • Bi-articular Muscles • Ligaments • Bone-Bone Contact • Set up optimization problem • Solve to get Muscle forces

  7. Forward Dynamic Model • Give muscle excitations • Find kinematics, resultant forces • How do we model muscle forces? • Hill Muscle Model F = Muscle Force F0 = Max Isometric Force v = Contraction Velocity a = Coefficent of Shortening Heat b = a* v0 /F0 v0 = Max velocity (F=0)

  8. What can we do with a Musculoskeletal Model? • Simulate Surgeries • Diagnose causes of atypical gait • Study Neuromuscular Coordination • Analyze Athletic Movements • Compute Internal Forces • Wear on Knee Replacements

  9. Software Demo

  10. How do we know the model is correct? • Must Validate! • Use Inverse Model to compute muscle activations • Compare against EMG data • Measure something in vivo • Bone contact force

  11. The eTibia

  12. A parameter study • What are the most important parameters to measure in a Subject Specific Model • Muscle Properties • Length • Cross sectional area • Pennation Angle • Origin and Insertion locations • Tendon Slack Length • Bone Properties • Dimensions • Joint kinematics • Segment Properties • Mass • Inertia • Joint constraints • Error in Marker Locations?

  13. The Coolest Models

  14. The End • Download Open Sim: www.simtk.org

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