This class serves as a serializable TendonForceLengthCurve for use in muscle models. More...

#include <TendonForceLengthCurve.h>

Inheritance diagram for OpenSim::TendonForceLengthCurve:

Public Member Functions
	TendonForceLengthCurve ()
	The default constructor creates a tendon-force-length curve using the default property values and assigns a default name.
	TendonForceLengthCurve (double strainAtOneNormForce, double stiffnessAtOneNormForce, double normForceAtToeEnd, double curviness)
	Constructs a tendon-force-length curve using the provided parameters and assigns a default name.
	TendonForceLengthCurve (double strainAtOneNormForce)
	This constructor will create a C2-continuous tendon-force-length curve that is fit to match the average dimensionless in-vivo tendon curve reported by Maganarius et al.
double	getStrainAtOneNormForce () const
double	getStiffnessAtOneNormForceInUse () const
double	getNormForceAtToeEndInUse () const
double	getCurvinessInUse () const
bool	isFittedCurveBeingUsed () const
void	setStrainAtOneNormForce (double aStrainAtOneNormForce)
void	setOptionalProperties (double aStiffnessAtOneNormForce, double aNormForceAtToeEnd, double aCurviness)
double	calcValue (const SimTK::Vector &x) const override
	Implement the generic OpenSim::Function interface.
double	calcValue (double aNormLength) const
	Evaluates the tendon-force-length curve at a normalized tendon length of 'aNormLength'.
double	calcDerivative (double aNormLength, int order) const
	Calculates the derivative of the tendon-force-length multiplier with respect to the normalized tendon length.
double	calcIntegral (double aNormLength) const
	Calculates the normalized area under the curve.
SimTK::Vec2	getCurveDomain () const
	Returns a SimTK::Vec2 containing the lower (0th element) and upper (1st element) bounds on the domain of the curve.
void	printMuscleCurveToCSVFile (const std::string &path)
	Generates a .csv file with a name that matches the curve name (e.g., "bicepsfemoris_TendonForceLengthCurve.csv").
void	ensureCurveUpToDate ()
Property declarations
These are the serializable properties associated with this class.
	OpenSim_DECLARE_PROPERTY (strain_at_one_norm_force, double,"Tendon strain at a tension of 1 normalized force")
	OpenSim_DECLARE_OPTIONAL_PROPERTY (stiffness_at_one_norm_force, double,"Tendon stiffness at a tension of 1 normalized force")
	OpenSim_DECLARE_OPTIONAL_PROPERTY (norm_force_at_toe_end, double,"Normalized force developed at the end of the toe region")
	OpenSim_DECLARE_OPTIONAL_PROPERTY (curviness, double,"Tendon curve bend, from linear (0) to maximum bend (1)")
Public Member Functions inherited from OpenSim::Function
	Function ()
	Function (const Function &aFunction)
virtual	~Function ()
virtual void	init (Function *aFunction)
Function &	operator= (const Function &aFunction)
virtual double	calcDerivative (const std::vector< int > &derivComponents, const SimTK::Vector &x) const
	Calculate a partial derivative of this function at a particular point.
virtual int	getArgumentSize () const
	Get the number of components expected in the input vector.
virtual int	getMaxDerivativeOrder () const
	Get the maximum derivative order this Function object can calculate.
virtual SimTK::Function *	createSimTKFunction () const =0
Public Member Functions inherited from OpenSim::Object
virtual	~Object ()
	Virtual destructor for cleanup.
virtual Object *	clone () 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 const VisibleObject *	getDisplayer () const
	Methods to support making the object displayable in the GUI or Visualizer Implemented only in few objects.
virtual VisibleObject *	updDisplayer ()
	get Non const pointer to VisibleObject
bool	isEqualTo (const Object &aObject) const
	Equality operator wrapper for use from languages not supporting operator overloading.
Object &	operator= (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 AbstractProperty &	getPropertyByIndex (int propertyIndex) const
	Get a const reference to a property by its index number, returned as an AbstractProperty.
AbstractProperty &	updPropertyByIndex (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 AbstractProperty &	getPropertyByName (const std::string &name) const
	Get a const reference to a property by its name, returned as an AbstractProperty.
AbstractProperty &	updPropertyByName (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	updateFromXMLNode (SimTK::Xml::Element &objectElement, int versionNumber)
	Use this method to deserialize an object from a SimTK::Xml::Element.
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.
PropertySet &	getPropertySet ()
	OBSOLETE: Get a reference to the PropertySet maintained by the Object.
const PropertySet &	getPropertySet () const

Additional Inherited Members
Static Public Member Functions inherited from OpenSim::Function
static Function *	makeFunctionOfType (Function *aFunction, const std::string &aNewTypeName)
Static Public Attributes inherited from OpenSim::Object
static const std::string	DEFAULT_NAME
	Name used for default objects when they are serialized.
Protected Member Functions inherited from OpenSim::Function
void	resetFunction ()
	This should be called whenever this object has been modified.
Protected Attributes inherited from OpenSim::Function
SimTK::Function *	_function
Related Functions inherited from OpenSim::Object
#define	OpenSim_DECLARE_CONCRETE_OBJECT(ConcreteClass, SuperClass)
	Macro to be included as the first line of the class declaration for any non-templatized, concrete class that derives from OpenSim::Object.
#define	OpenSim_DECLARE_ABSTRACT_OBJECT(ConcreteClass, SuperClass)
	Macro to be included as the first line of the class declaration for any still-abstract class that derives from OpenSim::Object.
#define	OpenSim_DECLARE_CONCRETE_OBJECT_T(ConcreteClass, TArg, SuperClass)
	Macro to be included as the first line of the class declaration for any templatized, concrete class that derives from OpenSim::Object, like Set<T>.
#define	OpenSim_DECLARE_ABSTRACT_OBJECT_T(ConcreteClass, TArg, SuperClass)
	Macro to be included as the first line of the class declaration for any templatized, still-abstract class that derives from OpenSim::Object.

Detailed Description

This class serves as a serializable TendonForceLengthCurve for use in muscle models.

The tendon-force-length curve is dimensionless: force is normalized to maximum isometric force and length is normalized to tendon slack length. The user can adjust the strain the tendon undergoes at 1 unit load (e0), its stiffness at a strain of e0, and the shape of the tendon curve (its 'curviness'):

Parameters

strainAtOneNormForce	The tendon strain at which the tendon develops 1 unit of normalized force. strainAtOneNormForce = 0.04 means that the tendon will develop a tension of 1 normalized force when it is strained by 4% of its slack length or, equivalently, is stretched to 1.04 times its resting length.
stiffnessAtOneNormForce	The normalized stiffness (slope of the tendon curve) when the tendon is strained by strainAtOneNormForce under a load of 1 normalized unit of force.
normForceAtToeEnd	The normalized force developed at the end of the 'toe' region. The toe region lies between 0 strain and some intermediate strain less than the strain required to develop 1 unit of normalized force. The toe region is nonlinear and more compliant than the rest of the tendon curve.
curviness	A dimensionless parameter between 0 and 1 that describes the shape of the curve: a value of 0 indicates that the curve is very close to a straight line segment and a value of 1 indicates a curve that smoothly fills the corner formed by the linear extrapolation of 'stiffnessAtOneNormForce' and the x-axis, as shown in the figure.

Note that we use the Cauchy or engineering definition of strain throughout: strain = (l-l0)/l0, where l is the current tendon length and l0 is its slack length.

Required Parameters

strainAtOneNormForce

Optional Parameters

stiffnessAtOneNormForce
normForceAtToeEnd
curviness

Conditions

   strainAtOneNormForce > 0
   stiffnessAtOneNormForce > 1/strainAtOneNormForce
   0 < normForceAtToeEnd < 1
   0 <= curviness <= 1

All parameters but the strain of the tendon at 1 unit load (e0) are optional. Note that filling in one optional parameter but not the others will throw an exception when the curve is built. The optional parameters can be used to vary the shape of the curve from a close approximation of a line to a sharply-bent curve.

This curve has the advantage of being C2-continuous, which results in faster simulations when compared to the popular method of using a linearly extrapolated exponential (C0-continuous) curve to parameterize the tendon-force-length relationship. See Millard et al. (2013) for details.

Default Parameter Values If the optional parameters are not specified, the curve is fit to match the average dimensionless in-vivo tendon curve reported by Maganarius et al. and Magnusson et al. In addition, the generated curve will have a characteristic toe region that is fit to the in-vivo literature. Note that this curve is not being fit to the commonly used linearly extrapolated exponential curve documented by Thelen, as it makes the toe region about half as stiff as both the in-vitro and in-vivo data indicate is reasonable. Additionally, the linear section of the curve would be nearly twice as stiff as the data indicates is reasonable.

   strainAtOneNormForce ....... 0.049
   stiffnessAtOneNormForce .... 1.375/strainAtOneNormForce
   normForceAtToeEnd .......... 2.0/3.0
   curviness .................. 0.5

Example

TendonForceLengthCurve fseCurve(0.049, 28.1, 0.67, 0.5);
double fseVal   = fseCurve.calcValue(0.02);
double dfselVal = fseCurve.calcDerivative(0.02, 1);

Note that this object should be updated through the set methods provided. These set methods will take care of rebuilding the curve correctly. If you modify the properties directly, the curve will not be rebuilt, and upon calling a function like calcValue, calcDerivative, or printCurveToCSVFile, an exception will be thrown because the curve is out-of-date with its properties.

References

Lewis, G., Shaw, K.M. (1997) Tensile properties of human tendo Achillis: effect of donor age and strain rate. The Journal of Foot and Ankle Surgery 36:435–445.
Maganaris, C.N., Paul, J.P. (2002) Tensile properties of the in vivo grastrocnemius tendon. Journal of Biomechanics 35:1639–1646.
Magnusson, S.P., Aagaard, P., Rosager, S., Dyhre-Poulsen, P., Kjaer, M. (2001) Load-displacement properties of the human triceps surae aponeurosis in vivo. Journal of Physiology 531:277–288.
Thelen, D.G. (2003) Adjustment of muscle mechanics model parameters to simulate dynamic contractions in older adults. ASME Journal of Biomechanical Engineering 125:70–77.

Author: Matt Millard

Constructor & Destructor Documentation

OpenSim::TendonForceLengthCurve::TendonForceLengthCurve ( )

The default constructor creates a tendon-force-length curve using the default property values and assigns a default name.

OpenSim::TendonForceLengthCurve::TendonForceLengthCurve	(	double	strainAtOneNormForce,
		double	stiffnessAtOneNormForce,
		double	normForceAtToeEnd,
		double	curviness
	)

Constructs a tendon-force-length curve using the provided parameters and assigns a default name.

OpenSim::TendonForceLengthCurve::TendonForceLengthCurve ( double strainAtOneNormForce )

This constructor will create a C2-continuous tendon-force-length curve that is fit to match the average dimensionless in-vivo tendon curve reported by Maganarius et al.

and Magnusson et al. In addition, the generated curve will have a characteristic toe region that is fit to the in-vivo literature.

Parameters

strainAtOneNormForce The tendon strain at which the tendon develops 1 unit of normalized force. strainAtOneNormForce = 0.04 means that the tendon will develop a tension of 1 normalized force when it is strained by 4% of its slack length or, equivalently, is stretched to 1.04 times its resting length.

Conditions

        strainAtOneNormForce > 0

Member Function Documentation

double OpenSim::TendonForceLengthCurve::calcDerivative	(	double	aNormLength,
		int	order
	)		const

Calculates the derivative of the tendon-force-length multiplier with respect to the normalized tendon length.

Parameters

aNormLength	The normalized length of the tendon.
order	The order of the derivative. Only values of 0, 1, and 2 are acceptable.

Returns: The derivative of the tendon-force-length curve with respect to the normalized tendon length.

double OpenSim::TendonForceLengthCurve::calcIntegral ( double aNormLength ) const

Calculates the normalized area under the curve.

Since it is expensive to construct, the curve is built only when necessary.

Parameters

aNormLength The normalized length of the tendon.

Returns: The normalized area under the curve, which corresponds to the normalized potential energy stored in the tendon. To calculate the potental energy stored in the tendon in units of Joules, multiply the returned quantity by normForce*normLength (where normForce is the number of Newtons represented by a normalized force of 1.0 and normLength is the number of meters represented by a normalized length of 1.0).

double OpenSim::TendonForceLengthCurve::calcValue ( const SimTK::Vector & x ) const

inlineoverridevirtual

Implement the generic OpenSim::Function interface.

Reimplemented from OpenSim::Function.

double OpenSim::TendonForceLengthCurve::calcValue ( double aNormLength ) const

Evaluates the tendon-force-length curve at a normalized tendon length of 'aNormLength'.

void OpenSim::TendonForceLengthCurve::ensureCurveUpToDate ( )

SimTK::Vec2 OpenSim::TendonForceLengthCurve::getCurveDomain ( ) const

Returns a SimTK::Vec2 containing the lower (0th element) and upper (1st element) bounds on the domain of the curve.

Outside this domain, the curve is approximated using linear extrapolation.

Returns: The minimum and maximum value of the domain, x, of the curve y(x). Within this range, y(x) is a curve; outside this range, the function y(x) is a C2-continuous linear extrapolation.

double OpenSim::TendonForceLengthCurve::getCurvinessInUse ( ) const

Returns: A dimensionless parameter between 0 and 1 that describes the shape of the curve: a value of 0 indicates that the curve is very close to a straight line segment and a value of 1 indicates a curve that smoothly fills the corner formed by the linear extrapolation of 'stiffnessAtOneNormForce' and the x-axis, as shown in the figure in the class description. This property is set to 0.5 by default.

double OpenSim::TendonForceLengthCurve::getNormForceAtToeEndInUse ( ) const

Returns: The normalized force developed at the end of the 'toe' region. The toe region lies between 0 strain and some intermediate strain less than the strain required to develop 1 unit of normalized force. The toe region is nonlinear and more compliant than the rest of the tendon curve. This property is set to 2.0/3.0 by default.

double OpenSim::TendonForceLengthCurve::getStiffnessAtOneNormForceInUse ( ) const

Returns: The normalized stiffness (slope of the tendon curve) when the tendon is strained by strainAtOneNormForce under a load of 1 normalized unit of force. This property is set to 1.375/strainAtOneNormForce by default.

double OpenSim::TendonForceLengthCurve::getStrainAtOneNormForce ( ) const

Returns: The tendon strain at which the tendon develops 1 unit of normalized force. strainAtOneNormForce = 0.04 means that the tendon will develop a tension of 1 normalized force when it is strained by 4% of its slack length or, equivalently, is stretched to 1.04 times its resting length. This property is set to 0.049 by default.

bool OpenSim::TendonForceLengthCurve::isFittedCurveBeingUsed ( ) const

Returns: True if the optional properties are empty and the fitted curve is being used, false if the optional properties are filled and are being used to construct the curve.

OpenSim::TendonForceLengthCurve::OpenSim_DECLARE_OPTIONAL_PROPERTY	(	stiffness_at_one_norm_force	,
		double	,
		"Tendon stiffness at a tension of 1 normalized force"
	)

OpenSim::TendonForceLengthCurve::OpenSim_DECLARE_OPTIONAL_PROPERTY	(	norm_force_at_toe_end	,
		double	,
		"Normalized force developed at the end of the toe region"
	)

OpenSim::TendonForceLengthCurve::OpenSim_DECLARE_OPTIONAL_PROPERTY	(	curviness	,
		double	,
		"Tendon curve	bend,
		from linear(0) to maximum bend(1)"
	)

OpenSim::TendonForceLengthCurve::OpenSim_DECLARE_PROPERTY	(	strain_at_one_norm_force	,
		double	,
		"Tendon strain at a tension of 1 normalized force"
	)

void OpenSim::TendonForceLengthCurve::printMuscleCurveToCSVFile ( const std::string & path )

Generates a .csv file with a name that matches the curve name (e.g., "bicepsfemoris_TendonForceLengthCurve.csv").

This function is not const to permit the curve to be rebuilt if it is out-of-date with its properties.

Parameters

path	The full destination path. Note that forward slashes ('/') must be used and there should not be a slash after the last folder.

The file will contain the following data:

column: 1 | 2 |     3 |       4
  data: x | y | dy/dx | d2y/dx2

Samples will be taken from the zero-force region, through the curve, out to strains beyond which the tendon generates normalized forces greater than 1. The curve is sampled quite densely: the tendon-force-length .csv file will have 200+20 rows.

Example To read the .csv file into Matlab, you need to set csvread to ignore the header row. Since csvread is 0-indexed, the following example will begin reading the .csv file from the first column of the second row:

data = csvread('bicepsfemoris_TendonForceLengthCurve.csv', 1, 0);

void OpenSim::TendonForceLengthCurve::setOptionalProperties	(	double	aStiffnessAtOneNormForce,
		double	aNormForceAtToeEnd,
		double	aCurviness
	)

Parameters

stiffnessAtOneNormForce	The normalized stiffness (slope of the tendon curve) when the tendon is strained by strainAtOneNormForce under a load of 1 normalized unit of force.
normForceAtToeEnd	The normalized force developed at the end of the 'toe' region. The toe region lies between 0 strain and some intermediate strain less than the strain required to develop 1 unit of normalized force. The toe region is nonlinear and more compliant than the rest of the tendon curve.
curviness	A dimensionless parameter between 0 and 1 that describes the shape of the curve: a value of 0 indicates that the curve is very close to a straight line segment and a value of 1 indicates a curve that smoothly fills the corner formed by the linear extrapolation of 'stiffnessAtOneNormForce' and the x-axis, as shown in the figure in the class description.

void OpenSim::TendonForceLengthCurve::setStrainAtOneNormForce ( double aStrainAtOneNormForce )

Parameters

aStrainAtOneNormForce The tendon strain at which the tendon develops 1 unit of normalized force. strainAtOneNormForce = 0.04 means that the tendon will develop a tension of 1 normalized force when it is strained by 4% of its slack length or, equivalently, is stretched to 1.04 times its resting length.

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

E:/Projects/OpenSimTrunk/OpenSim/Actuators/TendonForceLengthCurve.h

Public Member Functions

Additional Inherited Members

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation