The trickiest part is using the right strain with the right dosage. Do this wrong, and you may become a little lightheaded or too euphoric/lazy to move. Also, since both exercising and kratom dehydrates you, it's crucial to drink plenty of water before working out. I try to have at least a liter.
If you're interested in using kratom for other things, I have a growing list of these posts located here. If you have any questions or comments on other things you use kratom for, give me a shout on YouTube or my email address firstname.lastname@example.org