I am thinking that the exercise could have affected your cortisol levels, and thus affected your test. I know when I had mine tested about a year ago, I was in a VERY high stress situation at my parents house. My morning level was extremely low, but as the day went on, I was having to drink lots of caffeine to just keep functioning at the demands that were being made on me. So, when my testing was done, it showed higher levels in the afternoon and evening, even though my levels were still on the low side. I mentioned to my doc about the stress and caffeine on the testing day and so she definitely considered that the test was showing even higher levels of cortisol than would have been "normal."
When I did my last test, this past Jan., I tried to make sure that it was just a "normal" day for me, the least stress as possible, no caffeine or "energy" herbs, or anything like that. So, I think I had a much clearer picture this time. Maybe you could ask your doc about whether you should exercise on test day, but my inclination would be not to, since you are trying to get a picture of what your adrenals are doing as a whole, not when you exercise. Even in adrenal fatigue, your adrenals will release more cortisol under stress of any kind, including exercise, but I don't think that would be considered the "normal" state of the adrenals. Just like with drinking caffeine, etc., that should not be considered the normal state.
Hope this helps in some way. If anyone disagrees with my thoughts, please post so that we can get a better comprehension of this subject. Blessings.