A: Knee injury.
I'm about to give you really cool information about landing a jump and taking the stairs in a way that doesn't wonk your ankles, knees, and hips.
P.S. Yes, it is good to practice correcting your lands to change the loads to the knee, BUT it is even more important to practice your pelvic listing (<---check the "how to pelvic list" video in this post) and work on unschmearing so your muscle strength is carried with you at all times. This way, your jumping and stair-using is balanced naturally. Don't get me wrong, correcting the landing is helpful, but it's not really addressing the problem, which is chronic lateral hip and foot weakness.
So now that I've shared the aforementioned super-cool information I know that most of you really are wondering WHAT KIND OF BOOTS IS SHE WEARING IN THAT VIDEO? Because that's how you guys roll. And let's face it -- a zero-drop (no heel) winter-friendly kind of dressy boot is just about impossible to find. Here's the boot deets:
The boots in the video are actually a slight negative heel by Earth. They are called Invincible, but I've had them for about 4 years and they are the only non-positive heeled, semi-niceish looking boot I have ever found. You might be able to find some on ebay. If you are so lucky, they tend to run about 1/2 size large. I'm normally a 8.5 US.
Since there are way more companies out there now doing more minimal footwear, can anyone suggest a new company that has a zero-drop formal or kind of nice fashion boot? What about winter boot? What about men's shoes? If you've stumbled upon a great brand or style, please post a link below and I'll add these to my recommended shoe list.