In lv5 there is flutter kicks and crunches for the abs, and it says to do 10-20 flutter kicks, and 20 - 60 sec crunches. I think it supposed to be switched, but maybe not (I don't know for sure). and my question about flutter kicks is what this exercise supposed to train? lower abs or quads and hip flexors? (when I'm doing the flutter kicks I feel a little bit of abs and much more quads and hip flexors)
It trains both hip flexors and your abs. If you can only feel it in your hip flexors it could mean that you need to do this exercise more to get stronger hip flexors. If they are not used to a movement like this, they can cramp easily.