Fig. 1

Joint motion types. Three types of cervical joint motion 1) C 2) S and 3) A. The joint motion type C illustrates the common perception of joint motion from upright along the purple line to end-range. Type C joint motion has no pro-directional surplus motion. This type of motion is documented in almost half of all cervical joints. Type S joint motion is illustrated by the red line, and beyond end-range by the green line. Almost half of the joint motion in this study was type S. The green returning arrow illustrates that the motion passes the point of end-range, before the end of neck motion, and continues to the point of maximum surplus joint motion. It then moves anti-directionally towards the end-range position. Type A joint motion terminates in the opposite direction to that of head motion. This type of joint motion is demonstrated by approximately 6% of all cervical joints and is illustrated by the blue line