Most of the time we think of skiing in terms of movements over the horizontal, after all, we are essentially fastened to the slope by gravity, the need to stay in control, and fear of breaking bones & body parts.
However, our knees and legs can work our body in a vertical fashion. We bob up and down and in fact it is best that we do, a stiff bodied skier is a snow covered skier. If you have ever seen the freestyle mogul event in the Olympics the upper bodies of the skiers appears to be fairly still and steady, however, watch their legs and knees and you will see lots of vertical motion.
You protest saying you ski on groomed runs that are nice and regular. Sure, still there is fair amount of need to ski with vertical motion. The common name for such motions are up-unweighting and down-unweighting and essentially they help remove your weight from the engaged ski edges so you can unlock those ski edges from their current state of snow engagement and roll your skis over to the new set of edges.
The rest of this discussion focuses on up-unweighting.
However, when I am skiing on good firm and groomed snow there is little need to perform this action, but when conditions become more challenging due to more advanced terrain, higher speeds, deeper snow, or softer snow I find up & down unweighting to be techniques that make changing edges much easier. Last weekend (April 9, 2011) I was skiing in just such conditions, I started off with normal technique and edge changes were much more reluctant but as I picked up speed and started working the vertical plane more I found little problem in getting my edges changed.
How does it work? I have not really spent a whole lot of thought analyzing my technique here, as usually these methods do not come into play at slow speeds but at higher speed and more difficult terrain. However, up-unweighting is something I tend to do when I hit a roller, I see the roller coming and time my edge change as I hit the crest of the roller, the roller pushes up against the edges and I pop up and I change edges.
I am never standing up fully erect, the forces at play in the situation I describe above most likely cause my body to compress into a shorter configuration and I am not so much standing up erect, but mainly springing up to near erect. After the edge change I settle back into a more normal stance. If I am skiing well and aggressively I notice sometimes my skis come completely off of the snow pack, and when I am in such a groove skiing is very enjoyable.