I do believe you are looking for Woody Guthrie :)
If your doing moderate intensity workouts/physical activity your only focused on the thing your doing so the answer should be (DISTRACTED)
There are many reasons why Zachary can't concentrate. He might have something on his mind that is bothering him, he could be hungry, he could not have a lot of energy. The best thing Zachary could do to help the paper not suffer is leave his desk and paper alone for about a half an hour, and maybe eat something, or just take a break. Maybe take a nap to get some energy back up so that he can get everything he needs in his paper.