2. Methods
2.1. Modelling of racket-side upper limb and racket system
The racket-side upper limb was modelled as linked 3 rigid segments (upper arm, forearm and hand) that have 7
DOFs (3 for shoulder, 2 for elbow and 2 for wrist) considering anatomical constraint degrees of freedom at joint
axes, e.g. inversion/eversion axis of the elbow joint, and internal/external rotation of the wrist joint (Fig.1). The
racket model consisted of grip handle, racket shaft and face. The racket shaft was divided into a set of rigid
segments connecting to its adjacent segments via virtual joints (Fig.1). The grip handle segment was connected to
the hand segment via a virtual joint with 0 DOF.
2.2. Equation of motion for the system
The translational and rotational equations of motion for each segment of system can be summed up in a matrix
form as follows:
= + + ++ ext ext MV PF P F QN H G (1)
where M is the inertia matrix and V is the vector containing the translational and rotational velocity vectors of each
segment's CG, P and Pext are the coefficient matrices of vector F which contains all joint force vectors and of
external force vector Fext, Q is the coefficient matrix of vector N which contains moment vectors at all joints, H is
the vector containing gyro moment vectors of all segments, and G is the vector of the gravitational component.
The equation for constraint condition in which adjacent segments are connected by joint is expressed as follows:
CV 0 = (2)
where C is the geometric constraint coefficient matrix of the generalized velocity vector.
The geometric equations for constraint axes of joints, such as, inversion/eversion axis of the elbow and
internal/external rotation of the wrist joint can be expressed in matrix form as follows:
AV 0 =