Muscle-tendon length, velocity and moment arms from joint angles

Evaluates a musclePath() over one or more poses: MTU length L(theta), moment arms -dL/dtheta_j, and MTU lengthening velocity dL/dt = -sum_j r_j * omega_j. When the model carries hill parameters, rigid-tendon normalized fiber length and velocity are also returned.

Usage

muscleTendonKinematics(
  model,
  angles,
  angular_velocities = NULL,
  sampling_rate = NULL
)

Arguments

model: A musclePath() model.
angles: Joint angles in radians: a named numeric vector (single pose), or an n_frames x n_joints matrix / data frame / named list of curves with columns/names matching the model's joints.
angular_velocities: Joint angular velocities (rad/s), same shape as angles. If NULL for a trajectory, they are estimated from angles by central differences (requires sampling_rate); for a single pose they default to zero.
sampling_rate: Sampling rate (Hz) used to differentiate angles when angular_velocities is NULL.

Value

A muscle_tendon_kinematics object: a list with length (m), velocity (m/s), moment_arms (n_frames x n_joints, m), joints, and, when hill is set, norm_fiber_length and norm_fiber_velocity.

References

Zajac FE (1989). "Muscle and tendon: properties, models, scaling, and application to biomechanics and motor control." Thelen DG (2003).

Examples

mp <- musclePath("ankle", coefficients = list(ankle = c(-0.05, 0.01)),
                 slack_length = 0.3)
muscleTendonKinematics(mp, angles = c(ankle = 0.1),
                       angular_velocities = c(ankle = 2))
#> <muscle_tendon_kinematics> 1 frame(s)
#>   joints  : ankle 
#>   length  : 0.2951 .. 0.2951 m
#>   velocity: -0.0960 .. -0.0960 m/s