it doesnt hurt at all.. i'm not naturally flexible in my back so i had to work very hard to achieve it. at times it was uncomfortable, but once i was able to sit in a split and bend back to hold my back leg, it didnt hurt at all. i felt nothing, but not numb either. lol no discomfort! if you work on it everyday for a few hours a day, it will eventually come. but it comes much slower for those who do not have that natural flexibility.