It could be something as simple as asking you to touch your toes to having you on a message table and checking total flexibility from hamstrings to your hip flexor to IT bands. While non of these tests will give the fitter all the information he needs to do the fit they are like pieces of the puzzle. Flex tests help the fitter in making decisions such as bar reach and height. It can also help point out physical problems that you may or not be aware of such as leg length discrepancy's and pelvic rotations.....