Not only about the alignment of bones, but also for danger of blood clots from sitting in one place too long. I have heard it recommended that you set up your ironing board so that you have to get up from your chair to use it. That way you are forced to get up and move your legs. For older people this is especially important. Just like when you ride in a car or take a long plane trip. You gotta move it, girls!!! Get up and shake those legs!! LOL