Woofy.."I do some of my best thinking when doing things like heavy gardening work."
I would have thought that "thinking" and learning were two separate processes, but i may well be wrong.
Again, not being an expert but during exercise your blood oxygen levels fall and the relative anoxia stimulates the medulla to increase your heart rate and pulse rate to keep up the oxygen in your blood....
i.e it flogs itself to keep blood O2 acceptable.
That surely can't help the brain during the learning process...particularly in kids.