This hamstring stretching device was invented by Steve Nichols, the inventor of the Jacobs Ladder exercise machine.  It is true that "necessity is the mother of invention."  Steve's hamstrings were almost always tight and sore.  The only way to get a comfortable and effective stretch was to have another person push the leg back.  The big trick was coming up with a way of keeping the knee from bending.  An extra bonus was having the ability to do PNFs or isometrics.

In the process of researching hamstrings it was discovered that Steve's left hamstring was much tighter than his right.  This caused the pelvis to tilt to the left.  This in turn caused his lower spine to slide out of place, sending him to the chiropractor twice a month.  Since doing a lot of stretching, doctor visits have been reduced significantly.