The zFiber node is used to convert a generic tissue to a “muscle” by adding a fiber field. The fiber field is a user-specified vector field through the volume of the tissue that defines the direction that the muscle will contract.

Attribute Meaning
envelope Attenuates the excitation of this fiber node.
strength Defines the strength of the muscle. This is similar to the Young’s modulus parameter on the material node. The unit for muscle force is: N/m^2 (Newtons divided by meters squared).
strengthExp The power to which the value of the strength is raised.
contractionLimit The muscle’s contraction force works to make the muscle this fraction of its initial length. If this is set to 0.0, the muscle will seek to collapse into nothing. If this is 0.5, the muscle will seek to be half its initial length. If this is set to 1.0, the muscle will seek to be its initial length.
excitation Controls the amount of muscle contraction. A value of “0.0” is relaxed and “1.0” is fully contracted.
enableMuscleGrowth Turns muscle growth on/off.
muscleGrowthScale Sets the amount of muscle growth. This is a scaling factor; value must be > 0. Value of 1.0 means no growth. A value > 1.0 (e.g., 1.2, 1.5, etc.) will cause the muscle to grow perpendicularly to the fiber. Values < 1.0 (e.g., 0.8) cause shrinkage. This can be used to make the muscle bulkier or leaner.
useLoaForMuscleGrowth When on, the muscleGrowthScale is internally multiplied with the line of action value. This makes it possible to drive muscle growth using line of action. When off, the muscleGrowthScale value is used directly.
endPoints This attribute is used to author the fiber direction field by painting 1.0 in-points and 0.0 out-points that define a gradient that the fibers will flow along. Regardless of what is painted, the map is rounded to 0.0, 0.5, and 1.0 before use.
weights A paintable attribute that is used to scale the effect of the fiber force through the volume. It allows one to localize the effect of the fiber field to certain parts of the tissue. As in the zMaterial node, if localized fiber attenuation is required, the tet mesh will need to have enough local detail to support the desired detail in the fiber field.