Did you know - An angle of 110-130 degrees between the torso and thighs places the least amount of stress on the low back.
Sitting in the recumbent position recommended above also has the added benefit of forcing the shoulders back and opening the chest for better breathing and oxygen transfer. A tapered back rest helps facilitate this by allowing the shoulders to move naturally.
Sitting in this reclined position allows the chair user to utilize the support of the backrest as the designers intended. Too often we are guilty of sitting on the front edge of our chair so that we can see our monitors and gain access to our keyboard which is sitting on top of the desk.
Being highly productive in this position is possible with the combined use of a keyboard tray & monitor arm, or alternatively with an adjustable height desk with a concave front that allows one to tuck oneself under the desk and support the forearms on the desk.