Question  Variable  Posibilities  Modeling Tool  Assumptions & Limitations  Applications 
Range of Motion, restricted motion, excessive motion  Joint Angles, Velocities  2D/3D, Helen Hayes, Cleveland, 6DoF joints  Linksegment model  Euler sequence dependence & gimbal lock  Pre/Post Assessment, documentation, outcome measures 
Spasticity  Muscletendon lengths  Maximum & minimum averaged length  Deformable model, 3D reconstruction ± radiographic, MRI images  Muscle origin & insertion anthropometry, skinbone artifact, muscle physiology  Planning treatment (e.g. surgery in Cerebral palsy) 
Direction & magnitude of muscle activity  Joint Moment
Electromyography 
Flexor/extensor
Ab/adductor In/external rotator 
Inverse Dynamics (needs force platform)
M_{p} = I.a  M_{d} + Rx_{p}(y_{p}  y_{CoM}) + Ry_{p}(x_{CoM}  x_{p}) + Rx_{d}(y_{d}  y_{CoM}) + Ry_{d}(x_{CoM } x_{d}) where p=proximal; d=distal; CoM = center of mass; a = angular acceleration 
Errors in joint center estimation, body segment parameters, error propagation  Identify weakness/spasticity, prosthetic alignment 
Joint loading  Joint Force  Magnitude
Direction 
Inverse Dynamics
Optimization 
Lever arms, force compartmentalization  Endoprosthesis design, arthritis/walking aid assessment 
Type of Contraction  Joint Power  Concentric
Eccentric 
Inverse Dynamics
P = Mw where w = angular velocity 
Filtering greatly affects peak amplitudes  Determine purpose of muscle activity (propulsion or braking) 
Energy Transfer  Segmental Energies  Potential
Linear kinetic Rotational kinetic 
Segmental equations of motion  Body segment parameters  Prosthetics 
Energy Consumption  Oxygen consumption, Physiological Cost (PCI)  Energy consumed (metabolic cost)
Change in Heart Rate from resting 
VO_{2}  Encumbrance of subject
Confounding variables (anxiety) 
Evaluation of Interventions (e.g. prostheticorthotic devices, surgery) 
Efficiency  Joint Energies  Generation
Absorption 
Integration of Joint Powers  No cocontraction, friction, energy storage  Efficiency of prosthetic components 
Direction of effort  Power Flow  Proximal
Distal Absorbed 
Passive & Active contributions to segmental power  Foot segment can be difficult to balance  Determining the role of muscle power bursts 
Destination of effort, source of motion  Induced Acceleration  Ipsilateral joint
Contralateral joint 
Coupled Dynamics
a = M^{1}(q)t  M^{1}C(q,w)  M^{1}G(q) 
Singularities due to problems in defining footfloor interaction  Determine source of a given moment & control strategies available 
Balance Control  Center of Pressure, Center of Mass, Base of Support  Postural Sway, anticipatory & reactive torques  Inverted Pendulum, Full body models, perturbation studies  Interpretation during locomotion  Falls in the Elderly, Quantification of Dysequilibrium 
What if...?  Dynamic (Forward) Simulation  Computed Joint Motion Trajectories  Lagrange, Kane  Initial conditions, often 2D, assume trajectories  Influences on swing phase knee flexion. 
Paraplegic Locomotion  Finite States Machines 
Functional Electrical Stimulation (FES), conventional orthoses, hybrids 
Rule base control, confusion matrices, accelerometers, force sensors, fuzzy logic, machine learning, neural networks  False positives & negative event detection  Neuroprostheses 
Walking machines
"I never satisfy myself unless I can make a mechanical model of a thing. If I can make a mechanical model I can understand it." (Lord Kelvin) 
Balance, forward motion, energy consumption  Passive Walking, reflexes, springlike properties of muscles, tendons  Inverted Pendulum, serieselastic actuators, limit cycles, micro gravity  Falling, instability  Test understanding, control hypotheses. 



Joint Angle 

Approx. neutral at contact
Dorsiflexes through stance Sudden plantarflexion at toeoff Rapid return to neutral 
Joint Angular Velocity 

High plantarflexor velocity at toeoff 
Center of Pressure  
Joint Moment 

Small dorsiflexor moment on contact
Rise in plantarflexor moment to a maximum in late stance 
Foot Power  
Shank Power  
Joint Power 

Small eccentric after contact
Large burst of concentric power in late stance ("pushoff") 
Power Flow  
Soleus Induced Acceleration  
Gastroc Induced Acceleration 