Prior to my ADHD diagnosis, I found that my symptoms were reduced after exercise. On a day when I took no medication, I did vigorous exercise for half an hour. An hour later I did a PASAT. The results were similar to my results on medication.
Although it was done on rodents, I think tests showing chemical changes in the brain after exercise are applicable to humans too. I think it also make sense that the genetic basis of ADHD makes us want to get up and go, and when we do we feel better.
I think I'll try doing a few minutes of exercise in the mornings before my meds kick in. It will help my symptoms a bit, and it's good for my health!