"Brute force" seems to be the way that works for me. I imagine the app as a personal trainer with the support and encouragement of a drill sergeant. Whenever I want to stop even though I know pushing harder isn't going to hurt me, I just imagine what my drill-sergeant-trainer would say to me for wanting to stop. My brain automatically yells at me and it motivates me to keep going because it's usually right. I haven't had to stop for a legitimate health reason yet and each time I push myself a little harder, I usually come out of it feeling great, and suddenly the next day doesn't seem so bad.
I'm apprehensive about tomorrow and since I'm changing my scenery, I don't know how well I will do. But I'm going to try!