Wall Hip flexor mobilization drill
I've used this a few times since Eric posted the vid and I have to say I like it, I prefer keeping the reps low ~6 per leg.
"And for crying out loud. Don't go into the pain cave. I can't stress this enough. Your Totem Animal won't be in there to help you. You'll be on your own. The Pain Cave is for cowards.
Pain is your companion, don't go hide from it."