Ankle Strength: You Don't Notice It Until You Are Missing It

Stairs are dangerous for me. I've spent some time trying to go down them on both feet very slowly, and I think my problems are entirely in ankle strength. I seem to have the range of motion to step down, but no physical strength to do so. I can't lift my own body weight onto the ball of my left foot. I can't even stand on my left food. Jumping is right out. All of these things seem related to ankle strength.