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OpenSim::Millard2012EquilibriumMuscle Class Reference

This class implements a configurable equilibrium muscle model, as described in Millard et al. (2013). More...

#include <Millard2012EquilibriumMuscle.h>

Inheritance diagram for OpenSim::Millard2012EquilibriumMuscle:
OpenSim::Muscle OpenSim::PathActuator OpenSim::Actuator OpenSim::Actuator_ OpenSim::Force OpenSim::ModelComponent OpenSim::Object

Public Member Functions

 Millard2012EquilibriumMuscle ()
 Default constructor.
 Millard2012EquilibriumMuscle (const std::string &aName, double aMaxIsometricForce, double aOptimalFiberLength, double aTendonSlackLength, double aPennationAngle)
 Constructs a functional muscle using default curves and activation model parameters.
bool getUseFiberDamping () const
double getFiberDamping () const
double getDefaultActivation () const
double getDefaultFiberLength () const
double getActivationTimeConstant () const
double getDeactivationTimeConstant () const
double getMinimumActivation () const
const ActiveForceLengthCurvegetActiveForceLengthCurve () const
const ForceVelocityCurvegetForceVelocityCurve () const
const FiberForceLengthCurvegetFiberForceLengthCurve () const
const TendonForceLengthCurvegetTendonForceLengthCurve () const
const
MuscleFixedWidthPennationModel
getPennationModel () const
double getMaximumPennationAngle () const
double getMinimumFiberLength () const
double getMinimumFiberLengthAlongTendon () const
double getTendonForceMultiplier (SimTK::State &s) const
double getFiberStiffnessAlongTendon (const SimTK::State &s) const
double getFiberVelocity (const SimTK::State &s) const
double getActivationDerivative (const SimTK::State &s) const
Array< std::string > getStateVariableNames () const final
SimTK::SystemYIndex getStateVariableSystemIndex (const std::string &stateVariableName) const final
void setMuscleConfiguration (bool ignoreTendonCompliance, bool ignoreActivationDynamics, double dampingCoefficient)
void setFiberDamping (double dampingCoefficient)
void setDefaultActivation (double activation)
void setActivation (SimTK::State &s, double activation) const
void setDefaultFiberLength (double fiberLength)
void setActivationTimeConstant (double activationTimeConstant)
void setDeactivationTimeConstant (double deactivationTimeConstant)
void setMinimumActivation (double minimumActivation)
void setActiveForceLengthCurve (ActiveForceLengthCurve &aActiveForceLengthCurve)
void setForceVelocityCurve (ForceVelocityCurve &aForceVelocityCurve)
void setFiberForceLengthCurve (FiberForceLengthCurve &aFiberForceLengthCurve)
void setTendonForceLengthCurve (TendonForceLengthCurve &aTendonForceLengthCurve)
void setFiberLength (SimTK::State &s, double fiberLength) const
double computeActuation (const SimTK::State &s) const final
void computeInitialFiberEquilibrium (SimTK::State &s) const override
 Computes the fiber length such that the fiber and tendon are developing the same force, distributing the velocity of the entire musculotendon actuator between the fiber and tendon according to their relative stiffnesses.
void computeFiberEquilibriumAtZeroVelocity (SimTK::State &s) const override
 Computes the fiber length such that the fiber and tendon are developing the same force, assuming velocities are zero.
Property declarations

These are the serializable properties associated with this class.

 OpenSim_DECLARE_PROPERTY (fiber_damping, double,"The linear damping of the fiber.")
 OpenSim_DECLARE_PROPERTY (default_activation, double,"Assumed initial activation level if none is assigned.")
 OpenSim_DECLARE_PROPERTY (default_fiber_length, double,"Assumed initial fiber length if none is assigned.")
 OpenSim_DECLARE_PROPERTY (activation_time_constant, double,"Activation time constant (in seconds).")
 OpenSim_DECLARE_PROPERTY (deactivation_time_constant, double,"Deactivation time constant (in seconds).")
 OpenSim_DECLARE_PROPERTY (minimum_activation, double,"Activation lower bound.")
 OpenSim_DECLARE_UNNAMED_PROPERTY (ActiveForceLengthCurve,"Active-force-length curve.")
 OpenSim_DECLARE_UNNAMED_PROPERTY (ForceVelocityCurve,"Force-velocity curve.")
 OpenSim_DECLARE_UNNAMED_PROPERTY (FiberForceLengthCurve,"Passive-force-length curve.")
 OpenSim_DECLARE_UNNAMED_PROPERTY (TendonForceLengthCurve,"Tendon-force-length curve.")
- Public Member Functions inherited from OpenSim::Muscle
 OpenSim_DECLARE_PROPERTY (max_isometric_force, double,"Maximum isometric force that the fibers can generate")
 OpenSim_DECLARE_PROPERTY (optimal_fiber_length, double,"Optimal length of the muscle fibers")
 OpenSim_DECLARE_PROPERTY (tendon_slack_length, double,"Resting length of the tendon")
 OpenSim_DECLARE_PROPERTY (pennation_angle_at_optimal, double,"Angle between tendon and fibers at optimal fiber length expressed in radians")
 OpenSim_DECLARE_PROPERTY (max_contraction_velocity, double,"Maximum contraction velocity of the fibers, in optimal fiberlengths/second")
 OpenSim_DECLARE_PROPERTY (ignore_tendon_compliance, bool,"Compute muscle dynamics ignoring tendon compliance. Tendon is assumed to be rigid.")
 OpenSim_DECLARE_PROPERTY (ignore_activation_dynamics, bool,"Compute muscle dynamics ignoring activation dynamics. Activation is equivalent to excitation.")
 Muscle ()
 Default constructor.
double getMaxIsometricForce () const
 get/set the maximum isometric force (in N) that the fibers can generate
void setMaxIsometricForce (double maxIsometricForce)
double getOptimalFiberLength () const
 get/set the optimal length (in m) of the muscle fibers (lumped as a single fiber)
void setOptimalFiberLength (double optimalFiberLength)
double getTendonSlackLength () const
 get/set the resting (slack) length (in m) of the tendon that is in series with the muscle fiber
void setTendonSlackLength (double tendonSlackLength)
double getPennationAngleAtOptimalFiberLength () const
 get/set the angle (in radians) between fibers at their optimal fiber length and the tendon
void setPennationAngleAtOptimalFiberLength (double pennationAngle)
double getMaxContractionVelocity () const
 get/set the maximum contraction velocity of the fibers, in optimal fiber-lengths per second
void setMaxContractionVelocity (double maxContractionVelocity)
bool getIgnoreTendonCompliance (const SimTK::State &s) const
 Get/set Modeling (runtime) option to ignore tendon compliance when computing muscle dynamics.
void setIgnoreTendonCompliance (SimTK::State &s, bool ignore) const
bool getIgnoreActivationDynamics (const SimTK::State &s) const
 Get/set Modeling (runtime) option to ignore activation dynamics when computing muscle dynamics.
void setIgnoreActivationDynamics (SimTK::State &s, bool ignore) const
virtual double getActivation (const SimTK::State &s) const
 get the activation level of the muscle, which modulates the active force of the muscle and has a normalized (0 to 1) value Note: method remains virtual to permit override by deprecated muscles.
double getFiberLength (const SimTK::State &s) const
 get the current working fiber length (m) for the muscle
double getPennationAngle (const SimTK::State &s) const
 get the current pennation angle (radians) between the fiber and tendon at the current fiber length
double getCosPennationAngle (const SimTK::State &s) const
 get the cosine of the current pennation angle (radians) between the fiber and tendon at the current fiber length
double getTendonLength (const SimTK::State &s) const
 get the current tendon length (m) given the current joint angles and fiber length
double getNormalizedFiberLength (const SimTK::State &s) const
 get the current normalized fiber length (fiber_length/optimal_fiber_length)
double getFiberLengthAlongTendon (const SimTK::State &s) const
 get the current fiber length (m) projected (*cos(pennationAngle)) onto the tendon direction
double getTendonStrain (const SimTK::State &s) const
 get the current tendon strain (delta_l/tendon_slack_length is dimensionless)
double getFiberPotentialEnergy (const SimTK::State &s) const
 the potential energy (J) stored in the fiber due to its parallel elastic element
double getTendonPotentialEnergy (const SimTK::State &s) const
 the potential energy (J) stored in the tendon
double getMusclePotentialEnergy (const SimTK::State &s) const
 the total potential energy (J) stored in the muscle
double getPassiveForceMultiplier (const SimTK::State &s) const
 get the passive fiber (parallel elastic element) force multiplier
double getActiveForceLengthMultiplier (const SimTK::State &s) const
 get the active fiber (contractile element) force multiplier due to current fiber length
double getNormalizedFiberVelocity (const SimTK::State &s) const
 get normalize fiber velocity (fiber_lengths/s / max_contraction_velocity)
double getFiberVelocityAlongTendon (const SimTK::State &s) const
 get the current afiber velocity (m/s) projected onto the tendon direction
double getPennationAngularVelocity (const SimTK::State &s) const
 get pennation angular velocity (radians/s)
double getTendonVelocity (const SimTK::State &s) const
 get the tendon velocity (m/s) positive is lengthening
double getForceVelocityMultiplier (const SimTK::State &s) const
 get the dimensionless multiplier resulting from the fiber's force-velocity curve
double getFiberForce (const SimTK::State &s) const
 get the current fiber force (N) applied to the tendon
double getFiberForceAlongTendon (const SimTK::State &s) const
 get the force of the fiber (N/m) along the direction of the tendon
double getActiveFiberForce (const SimTK::State &s) const
 get the current active fiber force (N) due to activation*force_length*force_velocity relationships
double getPassiveFiberForce (const SimTK::State &s) const
 get the current passive fiber force (N) passive_force_length relationship
double getActiveFiberForceAlongTendon (const SimTK::State &s) const
 get the current active fiber force (N) projected onto the tendon direction
double getPassiveFiberForceAlongTendon (const SimTK::State &s) const
 get the current passive fiber force (N) projected onto the tendon direction
double getTendonForce (const SimTK::State &s) const
 get the current tendon force (N) applied to bones
double getFiberStiffness (const SimTK::State &s) const
 get the current fiber stiffness (N/m) defined as the partial derivative of fiber force w.r.t.
double getTendonStiffness (const SimTK::State &s) const
 get the current tendon stiffness (N/m) defined as the partial derivative of tendon force w.r.t.
double getMuscleStiffness (const SimTK::State &s) const
 get the current muscle stiffness (N/m) defined as the partial derivative of muscle force w.r.t.
double getFiberActivePower (const SimTK::State &s) const
 get the current active fiber power (W)
double getFiberPassivePower (const SimTK::State &s) const
 get the current passive fiber power (W)
double getTendonPower (const SimTK::State &s) const
 get the current tendon power (W)
double getMusclePower (const SimTK::State &s) const
 get the current muscle power (W)
double getStress (const SimTK::State &s) const
 get the stress in the muscle (part of the Actuator interface as well)
void setExcitation (SimTK::State &s, double excitation) const
 set the excitation (control) for this muscle.
double getExcitation (const SimTK::State &s) const
void equilibrate (SimTK::State &s) const
 Find and set the equilibrium state of the muscle (if any)
- Public Member Functions inherited from OpenSim::PathActuator
 PathActuator ()
GeometryPathupdGeometryPath ()
const GeometryPathgetGeometryPath () const
virtual bool hasGeometryPath () const
 Return a flag indicating whether the Force is applied along a Path.
void setOptimalForce (double aOptimalForce)
double getOptimalForce () const
virtual double getLength (const SimTK::State &s) const
virtual double getLengtheningSpeed (const SimTK::State &s) const
virtual double getPower (const SimTK::State &s) const
void addNewPathPoint (const std::string &proposedName, OpenSim::Body &aBody, const SimTK::Vec3 &aPositionOnBody)
 Note that this function does not maintain the State and so should be used only before a valid State is created.
virtual double computeMomentArm (const SimTK::State &s, Coordinate &aCoord) const
virtual void updateFromXMLNode (SimTK::Xml::Element &aNode, int versionNumber=-1)
 Use this method to deserialize an object from a SimTK::Xml::Element.
virtual void preScale (const SimTK::State &s, const ScaleSet &aScaleSet)
virtual void scale (const SimTK::State &s, const ScaleSet &aScaleSet)
virtual const VisibleObjectgetDisplayer () const
 Methods to support making the object displayable in the GUI or Visualizer Implemented only in few objects.
virtual void updateDisplayer (const SimTK::State &s) const
 In case the ModelComponent has a visual representation (VisualObject), override this method to update it.
 OpenSim_DECLARE_UNNAMED_PROPERTY (GeometryPath,"The set of points defining the path of the muscle.")
 OpenSim_DECLARE_PROPERTY (optimal_force, double,"The maximum force this actuator can produce.")
- Public Member Functions inherited from OpenSim::Actuator
 Actuator ()
virtual double getControl (const SimTK::State &s) const
 Convenience method to set controls given scalar (double) valued control.
virtual int numControls () const
virtual void setForce (const SimTK::State &s, double aForce) const
virtual double getForce (const SimTK::State &s) const
virtual void setSpeed (const SimTK::State &s, double aspeed) const
virtual double getSpeed (const SimTK::State &s) const
void setMinControl (const double &aMinControl)
double getMinControl () const
void setMaxControl (const double &aMaxControl)
double getMaxControl () const
void overrideForce (SimTK::State &s, bool flag) const
 -------------------------------------------------------------------------- Overriding forces -------------------------------------------------------------------------- The force normally produced by an Actuator can be overriden and When the Actuator's force is overriden, the Actuator will by defualt produce a constant force which can be set with setOverrideForce().
bool isForceOverriden (const SimTK::State &s) const
 return Actuator's override status
void setOverrideForce (SimTK::State &s, double value) const
 set the force value used when the override is true
double getOverrideForce (const SimTK::State &s) const
 return override force
 OpenSim_DECLARE_PROPERTY (min_control, double,"Minimum allowed value for control signal. Used primarily when solving ""for control values.")
 Default is -Infinity (no limit).
 OpenSim_DECLARE_PROPERTY (max_control, double,"Maximum allowed value for control signal. Used primarily when solving ""for control values.")
 Default is Infinity (no limit).
- Public Member Functions inherited from OpenSim::Actuator_
 Actuator_ ()
virtual const SimTK::Vector getDefaultControls ()
 Actuator default controls are zero.
virtual const
SimTK::VectorView_< double > 
getControls (const SimTK::State &s) const
virtual void getControls (const SimTK::Vector &modelControls, SimTK::Vector &actuatorControls) const
 Convenience methods for getting, setting and adding to actuator controls from/into the model controls.
virtual void setControls (const SimTK::Vector &actuatorControls, SimTK::Vector &modelControls) const
 set actuator controls subvector into the right slot in the system-wide model controls
virtual void addInControls (const SimTK::Vector &actuatorControls, SimTK::Vector &modelControls) const
 add actuator controls to the values already occupying the slot in the system-wide model controls
virtual void computeEquilibrium (SimTK::State &s) const
- Public Member Functions inherited from OpenSim::Force
 Force (const Force &aForce)
 Implements a copy constructor just so it can invalidate the SimTK::Force index after copying.
Forceoperator= (const Force &aForce)
 Implements a copy assignment operator just so it can invalidate the SimTK::Force index after the assignment.
bool isDisabled (const SimTK::State &s) const
 Return if the Force is disabled or not.
void setDisabled (SimTK::State &s, bool disabled)
 Set the Force as disabled (true) or not (false).
 OpenSim_DECLARE_PROPERTY (isDisabled, bool,"Flag indicating whether the force is disabled or not. Disabled means"" that the force is not active in subsequent dynamics realizations.")
 A Force element is active (enabled) by default.
- Public Member Functions inherited from OpenSim::ModelComponent
 ModelComponent ()
 Default constructor.
 ModelComponent (const std::string &aFileName, bool aUpdateFromXMLNode=true) SWIG_DECLARE_EXCEPTION
 Construct ModelComponent from an XML file.
 ModelComponent (SimTK::Xml::Element &aNode)
 Construct ModelComponent from a specific node in an XML document.
 ModelComponent (const ModelComponent &source)
 Construct ModelComponent with its contents copied from another ModelComponent; this is a deep copy so nothing is shared with the source after the copy.
virtual ~ModelComponent ()
 Destructor is virtual to allow concrete model component cleanup.
ModelComponentoperator= (const ModelComponent &aModelComponent)
 Assignment operator to copy contents of an existing component.
const ModelgetModel () const
 Get a const reference to the Model this component is part of.
ModelupdModel ()
 Get a modifiable reference to the Model this component is part of.
virtual int getNumStateVariables () const
 Get the number of "Continuous" state variables maintained by the ModelComponent and its specified subcomponents.
int getModelingOption (const SimTK::State &state, const std::string &name) const
 Get a ModelingOption flag for this ModelComponent by name.
void setModelingOption (SimTK::State &state, const std::string &name, int flag) const
 Set the value of a ModelingOption flag for this ModelComponent.
double getStateVariable (const SimTK::State &state, const std::string &name) const
 Get the value of a state variable allocated by this ModelComponent.
void setStateVariable (SimTK::State &state, const std::string &name, double value) const
 Set the value of a state variable allocated by this ModelComponent by name.
double getDiscreteVariable (const SimTK::State &state, const std::string &name) const
 Get the value of a discrete variable allocated by this ModelComponent by name.
void setDiscreteVariable (SimTK::State &state, const std::string &name, double value) const
 Set the value of a discrete variable allocated by this ModelComponent by name.
template<typename T >
const T & getCacheVariable (const SimTK::State &state, const std::string &name) const
 Get the value of a cache variable allocated by this ModelComponent by name.
template<typename T >
T & updCacheVariable (const SimTK::State &state, const std::string &name) const
 Obtain a writable cache variable value allocated by this ModelComponent by name.
void markCacheVariableValid (const SimTK::State &state, const std::string &name) const
 After updating a cache variable value allocated by this ModelComponent, you can mark its value as valid, which will not change until the realization stage falls below the minimum set at the time the cache variable was created.
void markCacheVariableInvalid (const SimTK::State &state, const std::string &name) const
 Mark a cache variable value allocated by this ModelComponent as invalid.
bool isCacheVariableValid (const SimTK::State &state, const std::string &name) const
 Enables the to monitor the validity of the cache variable value using the returned flag.
template<typename T >
void setCacheVariable (const SimTK::State &state, const std::string &name, const T &value) const
 Set cache variable value allocated by this ModelComponent by name.
- Public Member Functions inherited from OpenSim::Object
virtual ~Object ()
 Virtual destructor for cleanup.
virtual Objectclone () const =0
 Create a new heap-allocated copy of the concrete object to which this Object refers.
virtual const std::string & getConcreteClassName () const =0
 Returns the class name of the concrete Object-derived class of the actual object referenced by this Object, as a string.
virtual VisibleObjectupdDisplayer ()
 get Non const pointer to VisibleObject
bool isEqualTo (const Object &aObject) const
 Equality operator wrapper for use from languages not supporting operator overloading.
Objectoperator= (const Object &aObject)
 Copy assignment copies he base class fields, including the properties.
virtual bool operator== (const Object &aObject) const
 Determine if two objects are equal.
virtual bool operator< (const Object &aObject) const
 Provide an ordering for objects so they can be put in sorted containers.
void setName (const std::string &name)
 Set the name of the Object.
const std::string & getName () const
 Get the name of this Object.
void setDescription (const std::string &description)
 Set description, a one-liner summary.
const std::string & getDescription () const
 Get description, a one-liner summary.
const std::string & getAuthors () const
 Get Authors of this Object.
void setAuthors (const std::string &authors)
 Set Authors of this object, call this method in your constructor if needed.
const std::string & getReferences () const
 Get references or publications to cite if using this object.
void setReferences (const std::string &references)
 Set references or publications to cite if using this object.
int getNumProperties () const
 Determine how many properties are stored with this Object.
const AbstractPropertygetPropertyByIndex (int propertyIndex) const
 Get a const reference to a property by its index number, returned as an AbstractProperty.
AbstractPropertyupdPropertyByIndex (int propertyIndex)
 Get a writable reference to a property by its index number, returned as an AbstractProperty.
bool hasProperty (const std::string &name) const
 Return true if this Object has a property of any type with the given name, which must not be empty.
const AbstractPropertygetPropertyByName (const std::string &name) const
 Get a const reference to a property by its name, returned as an AbstractProperty.
AbstractPropertyupdPropertyByName (const std::string &name)
 Get a writable reference to a property by its name, returned as an AbstractProperty.
template<class T >
bool hasProperty () const
 Return true if this Object contains an unnamed, one-object property that contains objects of the given template type T.
template<class T >
const Property< T > & getProperty (const PropertyIndex &index) const
 Get property of known type Property<T> as a const reference; the property must be present and have the right type.
template<class T >
Property< T > & updProperty (const PropertyIndex &index)
 Get property of known type Property<T> as a writable reference; the property must be present and have the right type.
void setObjectIsUpToDateWithProperties ()
 When an object is initialized using the current values of its properties, it can set a flag indicating that it is up to date.
bool isObjectUpToDateWithProperties () const
 Returns true if no property's value has changed since the last time setObjectIsUpToDateWithProperties() was called.
void readObjectFromXMLNodeOrFile (SimTK::Xml::Element &objectElement, int versionNumber)
 We're given an XML element from which we are to populate this Object.
virtual void updateXMLNode (SimTK::Xml::Element &parent)
 Serialize this object into the XML node that represents it.
bool getInlined () const
 Inlined means an in-memory Object that is not associated with an XMLDocument.
void setInlined (bool aInlined, const std::string &aFileName="")
 Mark this as inlined or not and optionally provide a file name to associate with the new XMLDocument for the non-inline case.
std::string getDocumentFileName () const
 If there is a document associated with this object then return the file name maintained by the document.
void setAllPropertiesUseDefault (bool aUseDefault)
bool print (const std::string &fileName)
 Write this Object into an XML file of the given name; conventionally the suffix to use is ".osim".
std::string dump (bool dumpName=false)
 dump the XML representation of this Object into an std::string and return it.
void clearObjectIsUpToDateWithProperties ()
 For testing or debugging purposes, manually clear the "object is up to date with respect to properties" flag.
virtual bool isA (const char *type) const
 The default implementation returns true only if the supplied string is "Object"; each Object-derived class overrides this to match its own class name.
const std::string & toString () const
 Wrapper to be used on Java side to display objects in tree; this returns just the object's name.
PropertySetgetPropertySet ()
 OBSOLETE: Get a reference to the PropertySet maintained by the Object.
const PropertySetgetPropertySet () const

Protected Member Functions

void postScale (const SimTK::State &s, const ScaleSet &aScaleSet)
double clampActivation (double activation) const
double calcActivationDerivative (double activation, double excitation) const
 Calculate activation rate.
double getStateVariableDeriv (const SimTK::State &s, const std::string &aStateName) const
 Gets the derivative of an actuator state by index.
void setStateVariableDeriv (const SimTK::State &s, const std::string &aStateName, double aValue) const
 Sets the derivative of an actuator state specified by name.
void calcMuscleLengthInfo (const SimTK::State &s, MuscleLengthInfo &mli) const override
 Calculate the position-related values associated with the muscle state (fiber and tendon lengths, normalized lengths, pennation angle, etc.).
void calcFiberVelocityInfo (const SimTK::State &s, FiberVelocityInfo &fvi) const override
 Calculate the velocity-related values associated with the muscle state (fiber and tendon velocities, normalized velocities, pennation angular velocity, etc.).
void calcMuscleDynamicsInfo (const SimTK::State &s, MuscleDynamicsInfo &mdi) const override
 Calculate the dynamics-related values associated with the muscle state (from the active- and passive-force-length curves, the force-velocity curve, and the tendon-force-length curve).
void calcMusclePotentialEnergyInfo (const SimTK::State &s, MusclePotentialEnergyInfo &mpei) const override
 Calculate the potential energy values associated with the muscle.
void connectToModel (Model &model) override
 Sets up the ModelComponent from the model, if necessary.
void addToSystem (SimTK::MultibodySystem &system) const override
 Creates the ModelComponent so that it can be used in simulation.
void initStateFromProperties (SimTK::State &s) const override
 Initializes the state of the ModelComponent.
void setPropertiesFromState (const SimTK::State &s) override
 Sets the default state for the ModelComponent.
SimTK::Vector computeStateVariableDerivatives (const SimTK::State &s) const override
 Computes state variable derivatives.
- Protected Member Functions inherited from OpenSim::Muscle
const MuscleLengthInfogetMuscleLengthInfo (const SimTK::State &s) const
 Developer Access to intermediate values calculate by the muscle model.
MuscleLengthInfoupdMuscleLengthInfo (const SimTK::State &s) const
const FiberVelocityInfogetFiberVelocityInfo (const SimTK::State &s) const
FiberVelocityInfoupdFiberVelocityInfo (const SimTK::State &s) const
const MuscleDynamicsInfogetMuscleDynamicsInfo (const SimTK::State &s) const
MuscleDynamicsInfoupdMuscleDynamicsInfo (const SimTK::State &s) const
const MusclePotentialEnergyInfogetMusclePotentialEnergyInfo (const SimTK::State &s) const
MusclePotentialEnergyInfoupdMusclePotentialEnergyInfo (const SimTK::State &s) const
void computeForce (const SimTK::State &state, SimTK::Vector_< SimTK::SpatialVec > &bodyForces, SimTK::Vector &generalizedForce) const override
 Force interface applies tension to bodies, and Muscle also checks that applied muscle tension is not negative.
double computePotentialEnergy (const SimTK::State &state) const override
 Potential energy stored by the muscle.
SimTK::Vec3 computePathColor (const SimTK::State &state) const override
 Override PathActuator virtual to calculate a preferred color for the muscle path based on activation.
virtual void updateGeometry (const SimTK::State &s)
- Protected Member Functions inherited from OpenSim::PathActuator
void realizeDynamics (const SimTK::State &state) const override
 Extension of parent class method; derived classes may extend further.
- Protected Member Functions inherited from OpenSim::Actuator
double computeOverrideForce (const SimTK::State &s) const
OpenSim::Array< std::string > getRecordLabels () const
 Methods to query a Force for the value actually applied during simulation The names of the quantities (column labels) is returned by this first function getRecordLabels()
OpenSim::Array< double > getRecordValues (const SimTK::State &state) const
 Given SimTK::State object extract all the values necessary to report forces, application location frame, etc.
- Protected Member Functions inherited from OpenSim::Actuator_
virtual void updateGeometry ()
- Protected Member Functions inherited from OpenSim::Force
 Force ()
 Default constructor sets up Force-level properties; can only be called from a derived class constructor.
 Force (SimTK::Xml::Element &node)
 Deserialization from XML, necessary so that derived classes can (de)serialize.
void applyForceToPoint (const SimTK::State &state, const OpenSim::Body &body, const SimTK::Vec3 &point, const SimTK::Vec3 &force, SimTK::Vector_< SimTK::SpatialVec > &bodyForces) const
 Apply a force at a particular point (a "station") on a given body.
void applyTorque (const SimTK::State &state, const OpenSim::Body &body, const SimTK::Vec3 &torque, SimTK::Vector_< SimTK::SpatialVec > &bodyForces) const
 Apply a torque to a particular body.
void applyGeneralizedForce (const SimTK::State &state, const Coordinate &coord, double force, SimTK::Vector &generalizedForces) const
 Apply a generalized force.
- Protected Member Functions inherited from OpenSim::ModelComponent
virtual void generateDecorations (bool fixed, const ModelDisplayHints &hints, const SimTK::State &state, SimTK::Array_< SimTK::DecorativeGeometry > &appendToThis) const
 Optional method for generating arbitrary display geometry that reflects this ModelComponent at the specified state.
virtual void realizeTopology (SimTK::State &state) const
 Obtain state resources that are needed unconditionally, and perform computations that depend only on the system topology.
virtual void realizeModel (SimTK::State &state) const
 Obtain state resources that may be needed, depending on modeling options, and perform computations that depend only on topology and selected modeling options.
virtual void realizeInstance (const SimTK::State &state) const
 Perform computations that depend only on instance variables, like lengths and masses.
virtual void realizeTime (const SimTK::State &state) const
 Perform computations that depend only on time and earlier stages.
virtual void realizePosition (const SimTK::State &state) const
 Perform computations that depend only on position-level state variables and computations performed in earlier stages (including time).
virtual void realizeVelocity (const SimTK::State &state) const
 Perform computations that depend only on velocity-level state variables and computations performed in earlier stages (including position, and time).
virtual void realizeAcceleration (const SimTK::State &state) const
 Perform computations that may depend on applied forces.
virtual void realizeReport (const SimTK::State &state) const
 Perform computations that may depend on anything but are only used for reporting and cannot affect subsequent simulation behavior.
void includeAsSubComponent (ModelComponent *aComponent)
 Include another ModelComponent as a Subcomponent of this ModelComponent.
void addModelingOption (const std::string &optionName, int maxFlagValue) const
 Add a modeling option (integer flag stored in the State) for use by this ModelComponent.
void addStateVariable (const std::string &stateVariableName, SimTK::Stage invalidatesStage=SimTK::Stage::Dynamics) const
 Add a continuous system state variable belonging to this ModelComponent, and assign a name by which to refer to it.
void addDiscreteVariable (const std::string &discreteVariableName, SimTK::Stage invalidatesStage) const
 Add a system discrete variable belonging to this ModelComponent, give it a name by which it can be referenced, and declare the lowest Stage that should be invalidated if this variable's value is changed.
template<class T >
void addCacheVariable (const std::string &cacheVariableName, const T &variablePrototype, SimTK::Stage dependsOnStage) const
 Add a state cache entry belonging to this ModelComponent to hold calculated values that must be automatically invalidated when certain state values change.
const int getStateIndex (const std::string &name) const
 Get the index of a ModelComponent's continuous state variable in the Subsystem for allocations.
const SimTK::DiscreteVariableIndex getDiscreteVariableIndex (const std::string &name) const
 Get the index of a ModelComponent's discrete variable in the Subsystem for allocations.
const SimTK::CacheEntryIndex getCacheVariableIndex (const std::string &name) const
 Get the index of a ModelComponent's cache variable in the Subsystem for allocations.
- Protected Member Functions inherited from OpenSim::Object
 Object ()
 The default constructor is only for use by constructors of derived types.
 Object (const std::string &fileName, bool aUpdateFromXMLNode=true) SWIG_DECLARE_EXCEPTION
 Constructor from a file, to be called from other constructors that take a file as input.
 Object (const Object &source)
 Copy constructor is invoked automatically by derived classes with default copy constructors; otherwise it must be invoked explicitly.
 Object (SimTK::Xml::Element &aElement)
 Construct the base class portion of an Object from a given Xml element that describes this Object.
template<class T >
PropertyIndex addProperty (const std::string &name, const std::string &comment, const T &value)
 Define a new single-value property of known type T, with the given name, associated comment, and initial value.
template<class T >
PropertyIndex addOptionalProperty (const std::string &name, const std::string &comment)
 Add an optional property, meaning it can contain either no value or a single value.
template<class T >
PropertyIndex addOptionalProperty (const std::string &name, const std::string &comment, const T &value)
 Add an optional property, meaning it can contain either no value or a single value.
template<class T >
PropertyIndex addListProperty (const std::string &name, const std::string &comment, int minSize, int maxSize)
 Define a new list-valued property of known type T, with the given name, associated comment, minimum (==0) and maximum (>0) allowable list lengths, and a zero-length initial value.
template<class T , template< class > class Container>
PropertyIndex addListProperty (const std::string &name, const std::string &comment, int minSize, int maxSize, const Container< T > &valueList)
 Define a new list-valued property as above, but assigning an initial value via some templatized container class that supports size() and indexing.
PropertyIndex getPropertyIndex (const std::string &name) const
 Look up a property by name and return its PropertyIndex if it is found.
template<class T >
PropertyIndex getPropertyIndex () const
 Look up an unnamed property by the type of object it contains, and return its PropertyIndex if it is found.
void updateFromXMLDocument ()
 Use this method only if you're deserializing from a file and the object is at the top level; that is, primarily in constructors that take a file name as input.
void setDocument (XMLDocument *doc)
 Unconditionally set the XMLDocument associated with this object.
const XMLDocumentgetDocument () const
 Get a const pointer to the document (if any) associated with this object.
XMLDocumentupdDocument ()
 Get a writable pointer to the document (if any) associated with this object.

Additional Inherited Members

- Static Public Member Functions inherited from OpenSim::Object
static void registerType (const Object &defaultObject)
 Register an instance of a class; if the class is already registered it will be replaced.
static void renameType (const std::string &oldTypeName, const std::string &newTypeName)
 Support versioning by associating the current Object type with an old name.
static const ObjectgetDefaultInstanceOfType (const std::string &concreteClassName)
 Return a pointer to the default instance of the registered (concrete) Object whose class name is given, or NULL if the type is not registered.
template<class T >
static bool isObjectTypeDerivedFrom (const std::string &concreteClassName)
 Return true if the given concrete object type represents a subclass of the template object type T, and thus could be referenced with a T*.
static ObjectnewInstanceOfType (const std::string &concreteClassName)
 Create a new instance of the concrete Object type whose class name is given as concreteClassName.
static void getRegisteredTypenames (Array< std::string > &typeNames)
 Retrieve all the typenames registered so far.
template<class T >
static void getRegisteredObjectsOfGivenType (ArrayPtrs< T > &rArray)
 Return an array of pointers to the default instances of all registered (concrete) Object types that derive from a given Object-derived type that does not have to be concrete.
static void PrintPropertyInfo (std::ostream &os, const std::string &classNameDotPropertyName)
 Dump formatted property information to a given output stream, useful for creating a "help" facility for registered objects.
static void PrintPropertyInfo (std::ostream &os, const std::string &className, const std::string &propertyName)
 Same as the other signature but the class name and property name are provided as two separate strings.
static ObjectmakeObjectFromFile (const std::string &fileName)
 Create an OpenSim object whose type is based on the tag at the root node of the XML file passed in.
static const std::string & getClassName ()
 Return the name of this class as a string; i.e., "Object".
static void setSerializeAllDefaults (bool shouldSerializeDefaults)
 Static function to control whether all registered objects and their properties are written to the defaults section of output files rather than only those values for which the default was explicitly overwritten when read in from an input file or set programmatically.
static bool getSerializeAllDefaults ()
 Report the value of the "serialize all defaults" flag.
static bool isKindOf (const char *type)
 Returns true if the passed-in string is "Object"; each Object-derived class defines a method of this name for its own class name.
static void setDebugLevel (int newLevel)
 Set the debug level to get verbose output.
static int getDebugLevel ()
 Get current setting of debug level.
static ObjectSafeCopy (const Object *aObject)
 Use the clone() method to duplicate the given object unless the pointer is null in which case null is returned.
static void RegisterType (const Object &defaultObject)
 OBSOLETE alternate name for registerType().
static void RenameType (const std::string &oldName, const std::string &newName)
 OBSOLETE alternate name for renameType().
- Static Public Attributes inherited from OpenSim::Object
static const std::string DEFAULT_NAME
 Name used for default objects when they are serialized.
- Protected Attributes inherited from OpenSim::Muscle
double _muscleWidth
 The assumed fixed muscle-width from which the fiber pennation angle can be calculated.
double _maxIsometricForce
 to support deprecated muscles
double _optimalFiberLength
double _pennationAngleAtOptimal
double _tendonSlackLength

Detailed Description

This class implements a configurable equilibrium muscle model, as described in Millard et al. (2013).

An equilibrium model assumes that the forces generated by the fiber and tendon are equal:

\[ f_{ISO}\Big(\mathbf{a}(t) \mathbf{f}_L(\hat{l}_{CE}) \mathbf{f}_V(\hat{v}_{CE}) + \mathbf{f}_{PE}(\hat{l}_{CE}) + \beta \hat{v}_{CE}\Big) \cos \phi - f_{ISO}\mathbf{f}_{SE}(\hat{l}_{T}) = 0 \]

fig_Millard2012EquilibriumMuscle.png

This model can be simulated in several configurations by adjusting three flags:

  • ignore_tendon_compliance: set to true to make the tendon rigid. This assumption is usually reasonable for short tendons, and can result in a performance improvement by eliminating high-frequency dynamics and removing the fiber length from the state vector.
  • ignore_activation_dynamics: set to true to use the excitation input as the activation signal. This results in faster simulations by reducing the size of the state vector.
  • fiber_damping: set to a value greater than 0.001 to include fiber damping in the model. The addition of damping reduces simulation time while allowing the muscle model to be more physiological (it can have an activation of zero, its active-force-length curve can go to zero, and its force-velocity curve can be asymptotic).

Elastic Tendon, No Fiber Damping

The most typical configuration used in the literature is to simulate a muscle with an elastic tendon, full fiber dynamics, and activation dynamics. The resulting formulation suffers from three singularities: $\mathbf{a}(t) \rightarrow 0$, $\phi \rightarrow 90^\circ$, and $ \mathbf{f}_L(\hat{l}_{CE}) \rightarrow 0 $. These situations are all handled in this model to ensure that it does not produce singularities and does not result in intolerably long simulation times.

Numerical singularities arise from the manner in which the equilibrium equation is rearranged to yield an ordinary differential equation (ODE). The above equation is rearranged to isolate $ \mathbf{f}_V(\hat{v}_{CE}) $. We then invert to solve for $ \hat{v}_{CE} $, which is then numerically integrated during a simulation:

\[ \hat{v}_{CE} = \mathbf{f}_V ^{-1} \Big( \frac{ ( \mathbf{f}_{SE}(\hat{l}_{T}) ) / \cos \phi - \mathbf{f}_{PE}(\hat{l}_{CE}) } { \mathbf{a}(t) \mathbf{f}_L(\hat{l}_{CE})} \Big) \]

The above equation becomes numerically stiff when terms in the denominator approach zero (when $\mathbf{a}(t) \rightarrow 0$, $\phi \rightarrow 90^\circ$, or $ \mathbf{f}_L(\hat{l}_{CE}) \rightarrow 0 $) or, additionally, when the slope of $\mathbf{f}_V ^{-1}$ is steep (which occurs at fiber velocities close to the maximum concentric and maximum eccentric fiber velocities).

Singularities can be managed by ensuring that the muscle model is always activated ( $\mathbf{a}(t) > 0$), the fiber will stop contracting when a pennation angle of 90 degrees is approached ( $\phi < 90^\circ$), and the fiber will also stop contracting as its length approaches a lower bound ( $ \hat{l}_{CE} > lowerbound$), which is typically around half the fiber's resting length (to ensure $ \mathbf{f}_L(\hat{l}_{CE}) > 0 $). The fiber is prevented from reaching unphysiological lengths or its maximum pennation angle using a unilateral constraint. Additionally, the force-velocity curve is modified so that it is invertible.

When an elastic tendon without fiber damping is selected, the minimum active-force-length value is set to 0.1, the minimum permissible activation is set to 0.01, and the maximum permissible pennation angle is set to acos(0.1) or 84.3 degrees. This is done as a convenience for the user to prevent the model from taking an unreasonable amount of time to simulate.

(Rigid Tendon) or (Elastic Tendon with Fiber Damping)

Neither of these formulations has any singularities. The lower bound of the active-force-length curve can be zero (min( $ \mathbf{f}_L(\hat{l}_{CE})) = 0 $), activation can be zero (i.e., the muscle can be turned off completely), and the force-velocity curve need not be invertible.

The rigid tendon formulation removes the singularities by ignoring the elasticity of the tendon. This assumption is reasonable for many muscles, but it is up to the user to determine whether this assumption is valid.

The formulation that uses an elastic tendon with fiber damping removes singularities by solving the equilibrium equation with Newton's method. This is possible because the partial derivative of the equilibrium equation with respect to fiber velocity is always positive if $ \beta > 0$ and, thus, Newton's method can find a solution to the equilibrium equation.

When either of these singularity-free formulations is selected, the minimum active-force-length value and the minimum permissible activation are set to zero. This is done as a convenience for the user, as these changes make the results of the model more realistic yet incur no performance penality. The maximum pennation angle is left as acos(0.1) or 84.3 degrees, as allowing higher pennation angles results in an increasingly stiff fiber velocity state as pennation angle increases.

Usage

This object should be updated through the set methods provided.

Example

double maxIsometricForce = 5000; //N
double optimalFiberLength = 0.025; //m
double tendonSlackLength = 0.25; //m
double pennationAngle = 0.5; //rad
bool ignoreTendonCompliance = false;
bool ignoreActivationDynamics = false;
double dampingCoefficient = 0.001;
Millard2012EquilibriumMuscle myMuscle("myMuscle",
maxIsometricForce,
optimalFiberLength,
tendonSlackLength,
pennationAngle);
myMuscle.setMuscleConfiguration(ignoreTendonCompliance,
ignoreActivationDynamics,
dampingCoefficient);

Please refer to the doxygen for more information on the properties that are objects themselves (MuscleFixedWidthPennationModel, ActiveForceLengthCurve, FiberForceLengthCurve, TendonForceLengthCurve, and ForceVelocityInverseCurve).

Reference

Millard, M., Uchida, T., Seth, A., Delp, S.L. (2013) Flexing computational muscle: modeling and simulation of musculotendon dynamics. ASME Journal of Biomechanical Engineering 135(2):021005. http://dx.doi.org/10.1115/1.4023390.

Author
Matt Millard
Tom Uchida
Ajay Seth

Constructor & Destructor Documentation

OpenSim::Millard2012EquilibriumMuscle::Millard2012EquilibriumMuscle ( )

Default constructor.

Produces a non-functional empty muscle.

OpenSim::Millard2012EquilibriumMuscle::Millard2012EquilibriumMuscle ( const std::string &  aName,
double  aMaxIsometricForce,
double  aOptimalFiberLength,
double  aTendonSlackLength,
double  aPennationAngle 
)

Constructs a functional muscle using default curves and activation model parameters.

The tendon is assumed to be elastic, full fiber dynamics are solved, and activation dynamics are included.

Parameters
aNameThe name of the muscle.
aMaxIsometricForceThe force generated by the muscle when fully activated at its optimal resting length with a contraction velocity of zero.
aOptimalFiberLengthThe optimal length of the muscle fiber.
aTendonSlackLengthThe resting length of the tendon.
aPennationAngleThe angle of the fiber (in radians) relative to the tendon when the fiber is at its optimal resting length.

Member Function Documentation

void OpenSim::Millard2012EquilibriumMuscle::addToSystem ( SimTK::MultibodySystem &  system) const
overrideprotectedvirtual

Creates the ModelComponent so that it can be used in simulation.

Reimplemented from OpenSim::Muscle.

double OpenSim::Millard2012EquilibriumMuscle::calcActivationDerivative ( double  activation,
double  excitation 
) const
protected

Calculate activation rate.

void OpenSim::Millard2012EquilibriumMuscle::calcFiberVelocityInfo ( const SimTK::State &  s,
FiberVelocityInfo fvi 
) const
overrideprotectedvirtual

Calculate the velocity-related values associated with the muscle state (fiber and tendon velocities, normalized velocities, pennation angular velocity, etc.).

Reimplemented from OpenSim::Muscle.

void OpenSim::Millard2012EquilibriumMuscle::calcMuscleDynamicsInfo ( const SimTK::State &  s,
MuscleDynamicsInfo mdi 
) const
overrideprotectedvirtual

Calculate the dynamics-related values associated with the muscle state (from the active- and passive-force-length curves, the force-velocity curve, and the tendon-force-length curve).

Reimplemented from OpenSim::Muscle.

void OpenSim::Millard2012EquilibriumMuscle::calcMuscleLengthInfo ( const SimTK::State &  s,
MuscleLengthInfo mli 
) const
overrideprotectedvirtual

Calculate the position-related values associated with the muscle state (fiber and tendon lengths, normalized lengths, pennation angle, etc.).

Reimplemented from OpenSim::Muscle.

void OpenSim::Millard2012EquilibriumMuscle::calcMusclePotentialEnergyInfo ( const SimTK::State &  s,
MusclePotentialEnergyInfo mpei 
) const
overrideprotectedvirtual

Calculate the potential energy values associated with the muscle.

Reimplemented from OpenSim::Muscle.

double OpenSim::Millard2012EquilibriumMuscle::clampActivation ( double  activation) const
protected
Returns
Activation clamped to the permissible range (i.e., between minimum_activation and 1.0).
double OpenSim::Millard2012EquilibriumMuscle::computeActuation ( const SimTK::State &  s) const
virtual
Parameters
[in]sThe state of the system.
Returns
The tensile force the muscle is generating (N).

Implements OpenSim::Muscle.

void OpenSim::Millard2012EquilibriumMuscle::computeFiberEquilibriumAtZeroVelocity ( SimTK::State &  s) const
overridevirtual

Computes the fiber length such that the fiber and tendon are developing the same force, assuming velocities are zero.

This is a static equilibrium version of computeInitialFiberEquilibrium(). By setting velocities to zero, we obtain a reasonable and robust solution that provides a rough solution for fiber length.

Parameters
[in,out]sThe state of the system.

Reimplemented from OpenSim::Muscle.

void OpenSim::Millard2012EquilibriumMuscle::computeInitialFiberEquilibrium ( SimTK::State &  s) const
overridevirtual

Computes the fiber length such that the fiber and tendon are developing the same force, distributing the velocity of the entire musculotendon actuator between the fiber and tendon according to their relative stiffnesses.

Parameters
[in,out]sThe state of the system.

Implements OpenSim::Muscle.

SimTK::Vector OpenSim::Millard2012EquilibriumMuscle::computeStateVariableDerivatives ( const SimTK::State &  s) const
overrideprotectedvirtual

Computes state variable derivatives.

Reimplemented from OpenSim::ModelComponent.

void OpenSim::Millard2012EquilibriumMuscle::connectToModel ( Model model)
overrideprotectedvirtual

Sets up the ModelComponent from the model, if necessary.

Reimplemented from OpenSim::Muscle.

double OpenSim::Millard2012EquilibriumMuscle::getActivationDerivative ( const SimTK::State &  s) const
Parameters
sThe state of the system.
Returns
The time derivative of activation.
double OpenSim::Millard2012EquilibriumMuscle::getActivationTimeConstant ( ) const
Returns
The activation time constant (in seconds).
const ActiveForceLengthCurve& OpenSim::Millard2012EquilibriumMuscle::getActiveForceLengthCurve ( ) const
Returns
The ActiveForceLengthCurve used by this model.
double OpenSim::Millard2012EquilibriumMuscle::getDeactivationTimeConstant ( ) const
Returns
The deactivation time constant (in seconds).
double OpenSim::Millard2012EquilibriumMuscle::getDefaultActivation ( ) const
Returns
The default activation level that is used as an initial condition if none is provided by the user.
double OpenSim::Millard2012EquilibriumMuscle::getDefaultFiberLength ( ) const
Returns
The default fiber length that is used as an initial condition if none is provided by the user.
double OpenSim::Millard2012EquilibriumMuscle::getFiberDamping ( ) const
Returns
The fiber damping coefficient.
const FiberForceLengthCurve& OpenSim::Millard2012EquilibriumMuscle::getFiberForceLengthCurve ( ) const
Returns
The FiberForceLengthCurve used by this model.
double OpenSim::Millard2012EquilibriumMuscle::getFiberStiffnessAlongTendon ( const SimTK::State &  s) const
Returns
The stiffness of the muscle fibers along the tendon (N/m).

Reimplemented from OpenSim::Muscle.

double OpenSim::Millard2012EquilibriumMuscle::getFiberVelocity ( const SimTK::State &  s) const
Parameters
sThe state of the system.
Returns
The velocity of the fiber (m/s).

Reimplemented from OpenSim::Muscle.

const ForceVelocityCurve& OpenSim::Millard2012EquilibriumMuscle::getForceVelocityCurve ( ) const
Returns
The ForceVelocityCurve used by this model.
double OpenSim::Millard2012EquilibriumMuscle::getMaximumPennationAngle ( ) const
Returns
The maximum pennation angle permitted by this muscle model. Note that this equilibrium model, like all equilibrium models, has a singularity when pennation approaches Pi/2. Thus, the maximum pennation angle must be less than Pi/2.
double OpenSim::Millard2012EquilibriumMuscle::getMinimumActivation ( ) const
Returns
The minimum activation level permitted by the muscle model. Note that this equilibrium model, like all equilibrium models, has a singularity when activation approaches 0, which means that a non-zero lower bound is required.
double OpenSim::Millard2012EquilibriumMuscle::getMinimumFiberLength ( ) const
Returns
The minimum fiber length, which is the maximum of two values: the smallest fiber length allowed by the pennation model, and the minimum fiber length on the active-force-length curve. When the fiber reaches this length, it is constrained to this value until the fiber velocity becomes positive.
double OpenSim::Millard2012EquilibriumMuscle::getMinimumFiberLengthAlongTendon ( ) const
Returns
The minimum fiber length along the tendon, which is the maximum of two values: the smallest fiber length along the tendon permitted by the pennation model, and the minimum fiber length along the tendon on the active-force-length curve. When the fiber length reaches this value, it is constrained to this length along the tendon until the fiber velocity becomes positive.
const MuscleFixedWidthPennationModel& OpenSim::Millard2012EquilibriumMuscle::getPennationModel ( ) const
Returns
The MuscleFixedWidthPennationModel used by this model.
double OpenSim::Millard2012EquilibriumMuscle::getStateVariableDeriv ( const SimTK::State &  s,
const std::string &  aStateName 
) const
protected

Gets the derivative of an actuator state by index.

Parameters
sThe state.
aStateNameThe name of the state to get.
Returns
The value of the state derivative.
Array<std::string> OpenSim::Millard2012EquilibriumMuscle::getStateVariableNames ( ) const
virtual
Returns
A string array of the state variable names.

Reimplemented from OpenSim::ModelComponent.

SimTK::SystemYIndex OpenSim::Millard2012EquilibriumMuscle::getStateVariableSystemIndex ( const std::string &  stateVariableName) const
virtual
Parameters
stateVariableNameThe name of the state varaible in question.
Returns
The system index of the state variable in question.

Reimplemented from OpenSim::ModelComponent.

const TendonForceLengthCurve& OpenSim::Millard2012EquilibriumMuscle::getTendonForceLengthCurve ( ) const
Returns
The TendonForceLengthCurve used by this model.
double OpenSim::Millard2012EquilibriumMuscle::getTendonForceMultiplier ( SimTK::State &  s) const
Parameters
sThe state of the system.
Returns
The normalized force term associated with the tendon element, $\mathbf{f}_{SE}(\hat{l}_{T})$, in the equilibrium equation.
bool OpenSim::Millard2012EquilibriumMuscle::getUseFiberDamping ( ) const
Returns
A boolean indicating whether fiber damping is being used.
void OpenSim::Millard2012EquilibriumMuscle::initStateFromProperties ( SimTK::State &  s) const
overrideprotectedvirtual

Initializes the state of the ModelComponent.

Reimplemented from OpenSim::Muscle.

OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_PROPERTY ( fiber_damping  ,
double  ,
"The linear damping of the fiber."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_PROPERTY ( default_activation  ,
double  ,
"Assumed initial activation level if none is assigned."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_PROPERTY ( default_fiber_length  ,
double  ,
"Assumed initial fiber length if none is assigned."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_PROPERTY ( activation_time_constant  ,
double  ,
"Activation time constant (in seconds)."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_PROPERTY ( deactivation_time_constant  ,
double  ,
"Deactivation time constant (in seconds)."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_PROPERTY ( minimum_activation  ,
double  ,
"Activation lower bound."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_UNNAMED_PROPERTY ( ActiveForceLengthCurve  ,
"Active-force-length curve."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_UNNAMED_PROPERTY ( ForceVelocityCurve  ,
"Force-velocity curve."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_UNNAMED_PROPERTY ( FiberForceLengthCurve  ,
"Passive-force-length curve."   
)
OpenSim::Millard2012EquilibriumMuscle::OpenSim_DECLARE_UNNAMED_PROPERTY ( TendonForceLengthCurve  ,
"Tendon-force-length curve."   
)
void OpenSim::Millard2012EquilibriumMuscle::postScale ( const SimTK::State &  s,
const ScaleSet aScaleSet 
)
protectedvirtual

Reimplemented from OpenSim::PathActuator.

void OpenSim::Millard2012EquilibriumMuscle::setActivation ( SimTK::State &  s,
double  activation 
) const
virtual
Parameters
sThe state of the system.
activationThe desired activation level.

Implements OpenSim::Muscle.

void OpenSim::Millard2012EquilibriumMuscle::setActivationTimeConstant ( double  activationTimeConstant)
Parameters
activationTimeConstantThe activation time constant (in seconds).
void OpenSim::Millard2012EquilibriumMuscle::setActiveForceLengthCurve ( ActiveForceLengthCurve aActiveForceLengthCurve)
Parameters
aActiveForceLengthCurveThe ActiveForceLengthCurve used by the muscle model to scale active fiber force as a function of fiber length.
void OpenSim::Millard2012EquilibriumMuscle::setDeactivationTimeConstant ( double  deactivationTimeConstant)
Parameters
deactivationTimeConstantThe deactivation time constant (in seconds).
void OpenSim::Millard2012EquilibriumMuscle::setDefaultActivation ( double  activation)
Parameters
activationThe default activation level that is used to initialize the muscle.
void OpenSim::Millard2012EquilibriumMuscle::setDefaultFiberLength ( double  fiberLength)
Parameters
fiberLengthThe default fiber length that is used to initialize the muscle.
void OpenSim::Millard2012EquilibriumMuscle::setFiberDamping ( double  dampingCoefficient)
Parameters
dampingCoefficientDefine the fiber damping coefficient.
void OpenSim::Millard2012EquilibriumMuscle::setFiberForceLengthCurve ( FiberForceLengthCurve aFiberForceLengthCurve)
Parameters
aFiberForceLengthCurveThe FiberForceLengthCurve used by the muscle model to calculate the passive force the muscle fiber generates as a function of fiber length.
void OpenSim::Millard2012EquilibriumMuscle::setFiberLength ( SimTK::State &  s,
double  fiberLength 
) const
Parameters
[out]sThe state of the system.
fiberLengthThe desired fiber length (m).
void OpenSim::Millard2012EquilibriumMuscle::setForceVelocityCurve ( ForceVelocityCurve aForceVelocityCurve)
Parameters
aForceVelocityCurveThe ForceVelocityCurve used by the muscle model to calculate the derivative of fiber length.
void OpenSim::Millard2012EquilibriumMuscle::setMinimumActivation ( double  minimumActivation)
Parameters
minimumActivationThe minimum permissible activation level.
void OpenSim::Millard2012EquilibriumMuscle::setMuscleConfiguration ( bool  ignoreTendonCompliance,
bool  ignoreActivationDynamics,
double  dampingCoefficient 
)
Parameters
ignoreTendonComplianceUse a rigid (true) or elastic tendon.
ignoreActivationDynamicsTreat the excitation input as the activation signal (true) or use a first-order activation dynamic model.
dampingCoefficientSpecify the amount of damping to include in the model (must be either 0 or greater than 0.001).
void OpenSim::Millard2012EquilibriumMuscle::setPropertiesFromState ( const SimTK::State &  s)
overrideprotectedvirtual

Sets the default state for the ModelComponent.

Reimplemented from OpenSim::Muscle.

void OpenSim::Millard2012EquilibriumMuscle::setStateVariableDeriv ( const SimTK::State &  s,
const std::string &  aStateName,
double  aValue 
) const
protected

Sets the derivative of an actuator state specified by name.

Parameters
sThe state.
aStateNameThe name of the state to set.
aValueThe value to which the state should be set.
void OpenSim::Millard2012EquilibriumMuscle::setTendonForceLengthCurve ( TendonForceLengthCurve aTendonForceLengthCurve)
Parameters
aTendonForceLengthCurveThe TendonForceLengthCurve used by the muscle model to calculate the force exerted by the tendon as a function of tendon length.

The documentation for this class was generated from the following file: