The entire article is misleading with regards to 135 degrees being optimum. They only tested 3 positions: hunched forward, straight up (90 degrees), and reclining (135 degrees). Not surprisingly, 135 degrees was better than the other two. But it's hardly optimum. They didn't test 95 degrees, 100 degrees, 130 degrees, etc., to find a true optimum. That's a study I'd like to see.
For the geometrically challenged, such as myself, the 135-degree thigh-back angle they mention can be more simply explained as reclining at a 45-degree angle. Isn't that easier to understand? They could have said that to begin with.