Last week, while tutoring a student, I had him toss a tennis ball back and forth. Before we did that, he was struggling with a problem; after he did it, he got the problem easily. Interesting.
I think tossing the tennis ball back and forth activated his brain by giving it some variation, requiring it control movement, and by getting blood — and his interest — flowing again.
Then, last Friday, I had him do some squats at one point, had him do ten pushups at another, had him toss a tennis ball at a third — and he did really well. He had more fun and more focus than in most other sessions in which he goes two hours sitting still.