They're nearly interchangeable. The difference is the usual difference between the present perfect and the simple past: do you want to emphasize the action's continued relevance for the present or not?
However, the fact that the speech is somewhat removed from the action in that verb flattens this nuance out. It would make more difference in this pair:
This is more exercise than I've ever done before.
This is more exercise than I ever did before.
Here, the second one seems to imply that there was an earlier period during which the speaker exercised, but then they took a break and haven't exercised for a while. Now they're starting a new regime. In the first sentence, on the other hand, they've probably continued exercising right up to the present.
I would expect it to be the same difference in your pair of sentences, except that since this latest exercise is already in the past, the present perfect seems to lose the insistence that the speaker exercised continuously up to that point. At least, that's my intuition.