ISB recommendation on definitions of joint coordinate system of various joints for the reporting of human joint motion – part I: ankle, hip, and spine. - Wu,G.; Siegler,S.; Allard,P.; Kirtley,C.; Leardini,A.; Rosenbaum,D.; Whittle,M.; D’Lima,D.; Cristofolini,L.; Witte,H.; Schmid,O.; Stoke,I. (J Biomech, 2002)