Stepping Issues

I'm still here! Its just my last week before the kids get back from Camp Grandma's and I'm trying to make the most of it!

So I'm having issues with stepping in Yang 64. I am so wobbly stepping into these sunken stances. I'm going through my notes trying to recall warm up exercises or leg strengthening exercises from when I started my practice.

Currently I feel like a toddler learning to walk from crawling. I know my stepping is supposed to go skin-muscle-bone, but I have to plant my heel hard otherwise I topple over. And its doubly frustrating because I'm not a schlob! I do 90 minute yoga classes. I run. I hiked 8 miles in the WV mountains this past weekend with no issues. Why's it so hard to take steps with bent knees?

Any suggestions gurus, sifus, masters?