Yay! I graduated from doing 10 Half Frogs at a time to 20 the other day. I definitely feel it in the upper and lower abs. But I also notice really feeling it in my quads. Lots of heat going on there!
I'm definitely curling the core, and making sure I'm not using momentum to bring my legs up. Also pressing lats down and doing W arms & pressing donut hands to the floor. So I'm just checking to see -- is this quad engagement appropriate, or do I need to tweak something?
Also, if what I'm doing is Half Frogs, what's a Whole Frog?