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Muscle moment arms

Source: R/muscle-tendon.R
momentArm.Rd

Returns muscle moment arms. With no model, this is the anatomical lookup table promoted from the package's internal reference values (signed by the agonist/antagonist direction); with a musclePath() model, the moment arm is the joint-angle-dependent value -dL/dtheta evaluated at angles.

Usage

momentArm(muscle = NULL, joint = NULL, model = NULL, angles = NULL)

Arguments

muscle

Optional muscle name to filter the lookup table (case insensitive). Ignored when model is supplied.

joint

Optional joint name to filter the lookup table.

model

Optional musclePath() model; when supplied, moment arms are computed from the path derivative at angles.

angles

Named numeric vector of joint angles in radians (one per joint the model crosses); required when model is supplied.

Value

Without model: a data frame with muscle_name, joint_name, moment_arm_m (magnitude), direction, and signed_moment_arm_m. With model: a named numeric vector of signed moment arms (m) per joint.

References

Sherman MA, Seth A, Delp SL (2013). "What is a moment arm? Calculating muscle effectiveness in biomechanical models using generalized coordinates."

See also

musclePath(), muscleTendonKinematics()

Examples

momentArm("Gastrocnemius")
#>      muscle_name joint_name moment_arm_m direction signed_moment_arm_m
#> 26 Gastrocnemius      ankle         0.05         1                0.05
mp <- musclePath("ankle", coefficients = list(ankle = c(-0.05)))
momentArm(model = mp, angles = c(ankle = 0.2))
#> ankle 
#>  0.05