A, Schematic illustration of postural manipulations for the on-axis and off-axis rotation conditions. In the on-axis condition, subjects were aligned with the vertical axis of the rotational turntable and motion of the head occurred about the C1–C2 vertebral axis. In the off-axis condition, the head was displaced forward (r = 8 cm) so that rotational movements occurred by producing lateral flexion at lower vertebral levels (C6–T3). B, Schematic illustration of the on-axis experimental paradigms that were used including WBT using the sled (see arrows denoting movement), WBR using the turntable, PNR using the turntable to rotate the body while the head was restrained to the ceiling, and HTR using the ceiling motor to rotate the head while the body was held stationary in space. Shown are as follows: (a) ceiling motor, (b) fixation point to connect the earth-vertical axis of rotation to the ceiling motor or ceiling, (c) vertical rod defining earth-vertical rotational axis, (d) fixation point on the trunk, (e) turntable, (f) sled, and (g) fixation point to connect rotational axis to head. C, Schematic illustration of the off-axis experimental paradigms that were used including EVA-WBR (A, top view illustration denotes the difference compared with WBR), EVA-PNR, and EVA-HTR.