Transcript Musculoskeletal Modeling

Musculoskeletal Modeling
Colin Smith
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
Musculoskeletal Models
• Approach the body like a Machine
• Model Bones as Rigid Bodies
• Model Muscles as actuators
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
Inverse Kinetics
• Solving the Equations of motion for each
segment, we can find the forces and moments
between each segment
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
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)
What can we do with a
Musculoskeletal Model?
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Simulate Surgeries
Diagnose causes of atypical gait
Study Neuromuscular Coordination
Analyze Athletic Movements
Compute Internal Forces
– Wear on Knee Replacements
Software Demo
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
The eTibia
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?
The Coolest Models
The End
• Download Open Sim:
www.simtk.org