Scaled ID approach versus AAN approach. (a) The scaled ID approach uses an estimation of the capability of the subject, which is the constant scaling factor of the peak task requirement. (b) The AAN approach estimates the capability of the subject using an MM. Due to the musculotendon properties and the coupling between joints in the MM, the relative capability with regards to the ID moment varies with the kinematics and the task requirements at the other joints. Therefore the capability varies in time during ADL.