Quick Core Circuit

The core is a vital part of the runner's body, but all too often neglected. In order to help myself focus more on this area, I created this core strengthening routine. I call it my "Quick Core Circuit" because it can be done fairly quickly. It consists of 3 sets of 7 exercises done in succession with no recovery time between each exercise. Each exercise focuses on a different part of the core, so even though you are not resting between exercises, each part is getting a break while another part is being worked. For me, each set takes 7-9 minutes, so the entire workout can be done in as little as 21 minutes. I started this routine a several weeks ago with fewer reps. Listed below is what I am currently doing.

1 - 30 Push ups
2 - 50 Crunches
3 - 60 second Plank
4 - 45 second Side Plank (each side)
5 - 15 Single Leg Hamstring Bridges (each leg)
6 - 30 Supermans
7 - 15 Single Leg Squats (each leg)

I've recently thrown in some clams and side leg lifts to strengthen my hips as I had been having some ITB trouble.

What do you do to strengthen your core?