where M is the mass matrix, k is the vector of generalized Coriolis and centrifugal forces, kG is the vector of generalized forces due to gravity, G transforms the horizontal Fx and vertical Fy components of the pushrim force (Fig. 1) in generalized forces, H transforms the shoulder moment τs and the elbow moment τe in generalized forces, and Q transforms the rolling resistance force Froll in generalized force. All the matrices in Eq. (2) are presented in Tab. 2 in the Appendix.