Did a little training session the other day to take some material which I have not done for a while.
Still have a lot to improve with the muscle-up; lot of kipping, but that'll get better with strength and technique. Mainly I'm still trying to fix the "chicken wing" – uneven elevation of elbows to the top of the bar, which is visible with the last reps. First one was pretty even though. I've been doing slow descending "negative muscle-ups" which should improve especially the transitioning phase from pull-up to push-up.
Human flag is pretty decent, the progress with it is now just the matter of improvement in strength to achieve the perfect horizontal form. It really hits the core, especially the sides, but what you might not realize is that you need a lot of pushing strength from the bottom hand – the whole weight of the body rests on top of it. That might actually be a bigger "bottle-neck" than core strength for me.
It's one interesting movement for body coordination, because with the bottom hand you have to push as hard as you can but with the top hand you have to pull as hard as you can with your lat (latissimus dorsi), the same large back muscle engaged in a pull-up, of course not to forgetting the core; without it you'll only have a sagging flag. (Fighting gravity ain't easy feat.) For it being asymmetrical movement, you need to train both sides equally not to have any uneven development. Left hand pushing strength has been a struggle for me and that's why I've done one set more with that as the bottom hand to catch up with the right hand.
Also, for a while I've been practicing my balance walking abilities which I showcase at the end of the video.
My video is at DLive