I've been working on this exercise for I think 6 months. maybe more.
I can't do even 1 correctly because I can't keep my knees locked out to any acceptable level of compression.
The limiting factor isn't my core strength I don't think -- it's my hamstrings and calves and to a less extent hips.
I've been working on improving my mobility very aggressively -- with some results. but not enough to do one of these properly.
any tips or advice greatly appreciated.