Oops, I'm sorry guys. I didn't know I was being asked anything.
Let me try to answer now:
But if you are using your hip flexors to raise your legs, why are your abs affected at all?
Well, technically, if you stand up and raise your leg, your abs don't really get used at all. I mean, through irridation (I think that's what Pavel calls it) you can get more tension in your hip flexors if you flex your abs, too, but strictly speaking, your abs don't do much.
If you're talking about laying leg raises, I think your abs fire to support your hips. Cuz try this: lay on the ground and raise only one leg. Your abs don't contract at all. Now raise both legs, feel your abs kick in? I think they're stabilizing your hips rather than raising your legs.
why when you do exercises working the hip flexors are the abs worked as well.
I think I just answered that above. If not, ask again.
Is it like a shoulder/bicep thing? And do hip flexors effect your kicks very much?
What shoulder bicep thing?
Hip flexors affect your kicks in the sense that they are responsible for raising your thighs, so whatever power and speed you can generate with them will carry over into that portion of the movement.
Iron