FLing was beating me a few years ago, i felt like my legs where too short (quiet JP!), after all they barely reach the ground whenst i'm standing.... So i decided to really work on it, and was developing a strategy of bringing them way up till the souls of my feats had to touch as my hips rotated out for more travel per stroke.
Well, long story to short (yes, i can actually do that!) that is the wrong angle of pull on the hip, and i kinda popped it outta joint. Believe me, you don't want to end up at emergency with that pain! It didn't come on till the next day, and actually i thought that i was getting the hang of FLing, and when i awoke in pain tried my trusty chiro, hours later went to a walkin clinic that gave me pain killers; about 4pm decided i shouldn't be playing hero, as i felt like i was blown apart on a mine field! The Demeral drip as i awoke was nice, but as i had gone into shock and passed out from the pain; i missed most of it! So i would kinda ad-vise one to keep their knees two-gather pretty much and not try any ariel yoga positions, at least i think it couda saved my FLing career!
When i 'body thrusting' i try to get a smooth rocking motion, whereby; my legs falling down power my chest and sholders up on the pivot of my waist, then i grab the line and hold it to my lil'chest and rock back letting that massive weightpull on the rope. i kinda got that idea from "On Rope" and there descriptions on how the hardest thing to efficient accsenion was keeping your chest/shoulder weight inline with the rope, so you weren't constantly fighting it falling out of line (they suggest a chest roller device), so all of your effort was focused moving up the rope. So i took this heavier/leveraged point and turned it into the power of lift! Between that, the 2/1 of the line and letting my lil'feats land on anything to take weight off the line; i do ok for an olde midget on short runs!
OK, i lied about the length, but balance in all things.......