Define a polynomial muscle-tendon path model

Describes muscle-tendon-unit (MTU) length as a polynomial in the joint angles the muscle crosses: $$L(\theta) = L_{slack} + \sum_j \sum_k c_{jk}\,\theta_j^{k}.$$ Moment arms follow as -dL/dtheta_j (Menegaldo et al. 2004). Supply hill parameters to enable normalized fiber length/velocity in muscleTendonKinematics().

Usage

musclePath(joints, coefficients, slack_length = 0, hill = NULL, muscle = NULL)

Arguments

joints

Character vector of joint names the muscle crosses.

coefficients

Named list (by joint) of polynomial coefficient vectors c(c1, c2, ...); the term of order k is c_k * theta^k (no constant term – put the length offset in slack_length). Angles are in radians, so coefficients carry units of m / rad^k.

slack_length

MTU length (m) at all-zero joint angles (default 0).

hill

Optional list with optimal_fiber_length, tendon_slack_length, pennation (rad, default 0) and max_contraction_velocity (optimal fiber lengths per second, default 10) for Hill-type fiber kinematics.

muscle

Optional muscle name (metadata).

Value

A muscle_path object.

References

Menegaldo LL, et al. (2004). J Biomech 37(9):1447-1453.

See also

muscleTendonKinematics(), defaultMusclePath()

Examples

# gastrocnemius crosses knee and ankle
musclePath(c("knee", "ankle"),
           coefficients = list(knee = c(0.03), ankle = c(-0.05, 0.01)),
           slack_length = 0.42)
#> <muscle_path> (unnamed) 
#>   joints      : knee, ankle 
#>   slack length: 0.42 m
#>   hill        : no