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 F 0 = Max Isometric Force v = Contraction Velocity a = Coefficent of Shortening Heat b = a* v 0 /F 0 v 0 = Max velocity (F=0)
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
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: