Prior to calculation of the instantaneous helical axes, for each sensor the position and angle time series were filtered with a cut-off frequency of 1.5 Hz. The Instantaneous Helical Axis was calculated for each time sample where the angular velocity of the distal segment, relative to the proximal segment was larger than 0.25 rad.s -1 . 1 Typical example for IHA calculations for elbow flexion, represented in the measurement co-ordinate system. The X-Z plane roughly corresponds with the frontal plane. IHA are drawn with a length of 2 cm.
Dots are data samples from the surfaces of humerus, ulna and radius.
2 Typical example for IHA calculations for forearm pronation, represented in the measurement co-ordinate system. The X-Z plane roughly corresponds with the frontal plane. IHA are drawn with a length of 2 cm. Dots are data samples from the surfaces of humerus, ulna and radius. Analogous to the position vector, the optimal direction vector v opt wascalculated as the vector with the smallest angle between axes.