All the bloods rushing to your head. take a break in between doing them dont just keep doing them all in a row or else you could faint.
Ive been practicing them for a while and im only just now starting to get them real good. I dont walk on them though i just go up and then sit there then come down. Ive been prolly working on them for like 2 months and i usually go up sit there for about like i dont know 5-10 seconds then come back down. its just practice to balance upside down. You dont need to hold them forever because they arent impressive but its good to learn how to adjust yourself to being upside down.
practice practice practice practice practice... thats all you can do really. I dont think theres any magic tip to doing them. Try going up fast and going up slow and keeping your legs bent at different angles or straighter... just practice.

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