MORE SITUPS AND CRUNCHES FOR A STRONGER CORE?
I was doing huge numbers of crunches of all sorts. And honestly, I had (I thought) good abdominal strength. Through a fluke, I noticed that when I took a week off of the gym, the hip pain went away. A dear friend, lower extremity / foot biomechanist, and pedorthist Shawn Eno of Xtreme Footwerks, told me that I should talk to a person he knew who was a BIOMECHANICS expert. I did, and the results of the changes that I made have been nothing short of amazing (I had something called "LOWER CROSSED SYNDROME").
My core strength routine consists of nothing but five minutes of so, three or four times a week, of Planks, Side Planks, Stir the Pot, and Bird Dogs. I even do some ball crunches while keeping my lower back in extension (sway back position). Oh; and I also do some KETTLEBELL SWINGS as well. My core is stronger than its ever been, and I am doing a fraction of the work. Oh, and no more hip flexor pain!