M or W-shape: Implications of axis definition for the accelerometer-based Timed-Up & Go Test.

To avoid confusion, we wish to clarify the definition used in ur recent study in which we reported on an accelerometer-based ssessment of the Timed Up and Go test [1]. We applied the conention of the accelerometer’s supplier and the frequently used natomical terminology. In this convention, anterior–posterior AP) refers to a movement from the front to the back so that positive AP acceleration reflects acceleration from the front o the back. If, instead, one would use the guidelines of the nternational Society of Biomechanics (ISB), where accelerations n the forward direction are assigned positive values, the Mike shape shown in Figs. 2 and 3 would become a W. Most f the results reported are independent of the sign of the sigal and, for those that are not, multiplication by −1 does not ffect the presence or absence of the group differences that we bserved. Thus, the key findings reported are essentially similar sing either definition. Nonetheless, it is important to keep this n mind when interpreting the results and comparing across studes.