Taking out the guess work:
With functional exercises, all tissue receives a stress because every muscle and joint is joined to every other muscle and joint. Therefore, with functional types of exercise, the body shows global stiffening when stressed. To account for this, you measure the flexibility of as many joints as possible with a ROM test that is easy to perform, repeatable, and measurable.
1) Close the eyes
2) Inhale fully and hold the breath
3) Tuck the chin to chest
4) Round forward (let arms and torso hang, do not intentionally stretch. Do not intentionally bend or straighten the knees either)
5) Open the eyes and observe ROM (When you are hanging at your furthest ROM, make a note of how far down your fingers come either on the box that you are standing on, or on your upper or lower leg, in which case you wouldn’t have to stand on any box)
If the ROM is shortened, you have created physical stress and you rest until the ROM is recovered. If the ROM is not short, then you either a) are only mentally challenged or b) you must change the technique to use more of your body.
Stay tuned for the scientific explanation!