Experimental determination of the instant screw axis and angular acceleration axis [biomechanics]

Least-squares algorithms for computing instant screw axis (ISA) and angular acceleration axis (AAA) parameters from position, velocity, and acceleration measurements for discrete landmarks on a rigid body are described. Instantaneous velocity and acceleration for each landmark are approximated using digital filtering and finite difference derivative computations applied to a sequence of experimental position measurements for that landmark. Results from the experimental verification of the algorithms are given