Fig. 3.

The rotation passive restraint envelope (with standard deviation, n=8), the points of mid-slack and the 5 N m measurement boundaries across a complete hip range of motion. It can be seen that there was a greater range of un-resisted rotation (space between the solid black lines) in mid-flexion and mid-ab/adduction than when the hip was deeply flexed/extended, or highly ab/adducted. It can also be seen that the hip was more open to internal rotation in extension, and external rotation in flexion as the mid-slack points (grey dots) shifted to external rotation as hip flexion was increased. However once the ligaments had started to restrain hip rotation, the internal/extenral rotation restraint is more symmetrical (equal spacing between solid black lines and dashed grey lines at each position).