In a 2006 study, Scottish radiologists confirmed that sitting up straight is bad for you, revealing that a 130-degree angle of recline between torso and thighs reduces pressure on the discs of the lower back. This is why the ubiquitous Aeron chair was so ahead of its time in 1994.
According to this article, however, designers have found that adjustment features on chairs like the Aeron are lost on most sitters. This has manufacturers focusing on designing a self-adjusting chair. Among the efforts noted is Humanscale’s Freedom Chair, which includes a counterbalance system that adjusts itself to the sitter’s weight as he or she reclines. Other experts have concluded that chairs contribute in part to the high rate of back pain affecting 8 out of 10 Americans. One designer notes that “Our notion of a machine for sitting may not make sense in a globalized world.” The author speculates that “Ten years from now, one worker may settle into a low recliner, another, will kneel on a soft carpet, and they’ll talk across a pile of office cushions.
Source: Peter Hall, Popular Science; Mar, 2007