Anyone use one of those "knee chairs?" -- or any other type of special chair?? My lower back starts screaming sometimes by the end of the trading day. This is a new thing (I guess hitting 40 will do that to you). I'm pretty active (running, volleyball, gym, etc) -- and this generally aggravates the back even more. I'm thinking that switching chairs would be a better idea than guzzling gin martinis to ease the pain!