I think something else that could have impacted their results is that for some people, the knowledge that they are being tested changes the way they think/perform quite drastically. When I sit at a desk and do menial work, I get restless and my productivity plummets. But if you tell me that I'm being assessed, and you give me a straightforward task, I will have no trouble focusing on it for at least an hour. Maybe treadmill desks help you stay on task, but at the same time inhibit your cognitive performance slightly.