Originally Posted by
Carbonfiberboy
In that video, he's basically doing 1-legged quarter squats. One-legged introduces more muscle activity for balancing, so it's harder than regular quarter squats and a plus, uses less weight to do it. Quarter and half squats produce the greatest strength improvements for cycling, though the limited range of motion may not be the best thing for one's knees. I'm usually in favor of full range of motion stuff but strength studies favor the quarter and half squats.
He also does full range exercises, I only used that video so there was no ambiguity in who I was referring to. It's a pretty interesting story of how he got into strengthening knees. Here's just one more of one of his many videos