Just a quick brain storm on how to conduct the screen, is the pelvis supposed to be fixed whilst performing this screen? If I get my clients to bend to reach their fists with their shoulders this can easily be achived. However, I have noticed clients use hip flexion to reach this distance. When I instruct my clients to not flex at the hip and to purely use flexion at the throacic and lumbar region I have never had a pass on this screen. So which method is the most precise measure of sagittal flexion?, with hip flexion, or without?. surely if the pelvis remains fixed and the emphesis is put on forward flexion through lumbar and thoracic regions this must give a more accurate result, but then the degree of "normal" flexion range of the thoracic and lumbar regions must be accounted for due to the limitations imposed by facet joints and spinal ligaments
Good question too...the test is, as you say, for spinal flexion, however functionally the pelvis will tilt with that movement to some degree. So we want to encourage more spinal flexion than pure hip flexion, however if they can achieve the require range of shoulder to thumbs with a reasonable degree of spinal flexion they are negative. If the client were to purely 'fold' or hip flex with a flat back I would challenge this being a negative result. Demo what you want them to do with verbal instruction and ask them to try again, if they still only flex at the hip then this would be a positive result.
This is one of those screens that will become easier to read the more you do and the more body types you assess.