An interesting little mobility test is to see how long you can sit in a 'third world squat' (Google it)... My goal at the moment is 10 minutes... Due to a lifetime of lower back issues, my mobility is surprisingly terrible due to muscular imbalances, I just managed to do 4 minutes in a TWS the other day. Actually, since I worked out what issues need to be resolved, I have managed to completely avoid injuring my back for over a year now
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I also started working on the planche, front lever, L-sits, and backflips... You want core strength? These things are killing me worse than deadlifts and squats ever have
. This is the website that is my inspiration:
http://www.dragondoor.com/articles/building-an-olympic-body-through-bodyweight-conditioning/
I've always had an interest in gymnastics though, and the other day I was sitting at work thinking "Why the hell can't I do backflips on flat ground after all these years?". So yeah, just putting that all out there... I seriously recommend giving some bodyweight gymnastics work a go - you'll probably discover you aren't nearly as strong as you thought you were