For me, strengthening my psoas muscles was the missing piece of the IT chain puzzle.
The psoas is the base of the IT chain pyramid. The 2nd layer of the pyramid is your external obliques, low abs and transversus abdominals. If your left psoas is weak, then typically the left external oblique is also weak. And your left quadratus lumborum probably has a history of going into spasm. Yes, they are related. The QL is likely the antagonist of the psoas.
I became more serious about strengthening my hip flexors when I enrolled in Pole Fitness Classes. I learned a lot of these exercises from my pole fitness teacher, and I've been sharing them with the StrongFit community. You'll notice I even use my pec stick, which you can get here.
I also like to do unilateral GHD sit ups with my pec stick to target my psoas. p.s. they are no joke.
Key points: Use your entire IT chain, focus on the isometric contraction, and don't forget to breathe!
If you want to learn about breathing and torque and how it impacts the way you move, and how I apply StrongFit to my home and gym workouts, then check out my ONLINE Strength Academy.