In regards to the "ISB recommendations for standardization in the reporting of kinematic data".

The ISB standards (Wu and Cavanagh, 1995) were intended to clarify the reporting of experimental results by standardizing the use of reference frames and orientation angles. However, the clarity is obscured by virtue of two di!erent standards being proposed. The di!ering standards arise from the fact that the orientation of a segment (e.g., the tibia) can be referenced to a global frame, `absolute orientationa or to a reference frame "xed in another segment (e.g., the femur), `relative orientationa. However, there are occasions when the global frame is the relative frame. This happens, for example, when the femoral system is aligned with and "xed in the global frame. In such a case, the ISB standard propose that researchers report one set of values if the femur is considered to be a relative frame and a di!erent set if the femur is considered to be the global frame. But these di!ering values correspond to the same orientation! We propose that a SINGLE standard should be adopted for reporting of all orientation angles, whether they are relative or absolute. The ISB standards add potential for misuse because the equations published by Grood and Suntay (1983) are inconsistent with the `joint coordinate systema proposed by the ISB. As noted by Grood and Suntay (1983), for every `joint coordinate systema there is a corresponding set of Euler angles that can be related to it. For example, it is easy to show that Grood and Suntay's `screw-axisa notation is simply a body-XYZ rotation sequence with a small modi"cation to Grood and Suntay's de"nition of h i (i"1, 2, 3). The proof of this fact is found in Sheehan (1997), but can be seen easily by de"ning for the right leg: