SY20: Modeling techniques in gait analysis

Yoshihira Ehara, The Kanagawa Rehabilitation Institute, Japan
Kenton Kaufman, The Mayo Clinic, USA
Chris Kirtley, Catholic University USA
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 Link-segment model Euler sequence dependence & gimbal lock Pre/Post Assessment, documentation, outcome measures
Spasticity Muscle-tendon lengths Maximum & minimum averaged length Deformable model, 3D reconstruction ± radiographic, MRI images Muscle origin & insertion anthropometry, skin-bone artifact, muscle physiology Planning treatment (e.g. surgery in Cerebral palsy)
Direction & magnitude of muscle activity Joint Moment
In/external rotator
Inverse Dynamics (needs force platform)
Mp = I.a - Md + Rxp(yp - yCoM) + Ryp(xCoM - xp) + Rxd(yd - yCoM) + Ryd(xCoM - xd)
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
Inverse Dynamics
Lever arms, force compartmentalization Endoprosthesis design, arthritis/walking aid assessment
Type of Contraction Joint Power Concentric
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
VO2 Encumbrance of subject
Confounding variables (anxiety)
Evaluation of Interventions (e.g. prostheticorthotic devices, surgery)
Efficiency Joint Energies Generation
Integration of Joint Powers No co-contraction, friction, energy storage Efficiency of prosthetic components
Direction of effort Power Flow Proximal
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-1C(q,w) - M-1G(q)
Singularities due to problems in defining foot-floor 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, series-elastic actuators, limit cycles, micro- gravity Falling, instability Test understanding, control hypotheses.


Example Applications

Ankle function in normal locomotion

Joint Angle
Approx. neutral at contact
Dorsiflexes through stance
Sudden plantarflexion at toe-off
Rapid return to neutral
Joint Angular Velocity
High plantarflexor velocity at toe-off
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 ("push-off")

Power Flow
Soleus Induced Acceleration
Gastroc Induced Acceleration

Clinical Case: #1. Right hemiparesis (cerebral palsy)

Weak & spastic (plantarflexed) ankle, with reduced push-off power



Muscle lengths

Inverse Dynamics

Balance Control


Induced Acceleration

Forward Simulation

Finite State Machines

Walking Machines