We've strayed pretty far from the original topic here. Understanding a skier's balance point in moguls as a variable certainly leaves many mystified. I'm probably not going to help by suggesting the CoM-BoS relationship is not all that important in the flexing phase across the ramp (uphill facet) of the mogul. Mostly due to the hyper variable nature of pressure in the bumps. Lesser skiers are often seen trying to check their speed with a movement that resembles the hop turn with strong edge sets. Better bump skiers know this only leads to getting launched upwards when they are trying to stay down. The net result is a loss of contact with the snow, especially in the troughs. A line I use often is they would be working at crossed purposes if they did that. But what should they replace that edge set with? How would they check their speed? I will cover speed control a bit later but for now let's assume they have that other speed control option down.
A strong retraction of the feet is quite common among good mogul skiers and this serves several purposes.
First and foremost as I have already mentioned, it prevents that mogul from launching them up in the air as they ski up the ramp (the upper facet of the mogul). So in much the same way as they would do a pre-jump maneuver in a race course they must also actively pre-jump that next mogul crest. As many will undoubtedly mention, strong leg flexing movements will swing the femur into a horizontal position, or at the very least parallel to the incidental slope angle. Since the tibia and fibula are attached they also will move forward. As will the feet and skis. Compensating for this under normal circumstances usually involves bending at the waist and moving the upper torso forward. This projects the CoM forward to a point outside the body and keeps the CoM and BoS aligned along the balance axis. That is how the theory suggest thing should work. But at the risk of being called a heretic again, I am suggesting here that a normal load isn't present at the mogul crest if they have flexed like the pre-jump maneuver I just mentioned. This makes the assumption of needing to align the CoM and BoS along the incidental balance axis a bit questionable.
Which brings me to the second thing to consider. When they flex so abruptly the inertial momentum of the skier is what is going to carry their torso over the mogul in a mostly linear path. Whatever lateral acceleration as well as any vertical acceleration they added was done well in advance of the ramp (upper facet of the mogul). So even though the skis may continue to turn across the hill their effect on the core's path is quite negligible. An idea very consistent with the U/L separation and the dual paths concept. What is different is that instead of being applied only to the rotational skill pool it is now being applied in the pressure control skill pool.
A third thing to consider is the need to maintain snow contact for speed control. Shaping that turn as the snow falls away from them requires a lot of leg extension down the downhill facet of the mogul and through the trough between moguls. Coincidentally they also need to do most of the redirecting work here as well. Some of that is from the rotary skill pool but to control speed some edge and pressure skills must be present as well. (see the counter thread for a more complete description of how we develop lateral reaction forces from the snow) This effort is identical to the tramp man maneuver where the strong shaping and pressure phase are near the fall line, as are the highest edge angles and most inclined stances (not to be confused with pure inclination) but since multiple fall lines exist in a mogul field they must instinctively figure out what the incidental fall line is and adjust their movements to it before quickly hitting the repeat button and starting the flexing process as they reach that next ramp.
From the observers perspective a skier on the ramp of the next bump certainly looks to be a bit aft but the incidental slope angle is flatter than the overall slope angle. So maybe they aren't quite so far aft after all. But here is where it gets a bit tricky, Add the active flexing of the legs that swings their lower legs forward and it very much looks like they are in an aft stance because they are. At least momentarily. Many coaches mistakenly worry about this too much and suggest their charges strongly flex the boots in a vain attempt to maintain that good fore aft alignment we hear and read so much about. Or they talk about pulling the feet back strongly to accomplish this same outcome. Both ideas are born out of the mistaken idea that a strong retraction move and the nearly weightless phase would require them to maintain that alignment of the CoM and BoS along the balance axis. Never mind the fact that the legs don't work that way and crushing the boot would add pressure when we are trying to reduce it with that strong pre jump move. The net result of that would again be they would be working at crossed purposes and it increases the likelihood of getting launched. Don't get me wrong, we still must maintain good foot discipline but this is where a too rigid interpretation of stance and alignment works against the situational needs of the pre jump move.
Hopefully by debunking the myth of maintaining CoM and BoS alignment along the balance axis during that pre-jump move we are free to discuss adopting a more centered stance during the brief strong pressure and edging phases that occur between the moguls. If you stay aft there, then it is likely a crash is in your immediate future. In MA practice concentrate on their stance during those strong pressure and edge phases and don't worry so much about it during the weightless phase . At least as long as they don't swing the feet forward from the knees as they flex to absorb the ramp.
I will shut up now and let the engineers run wild with equations and theories about centripetal. centrifugal, at a distance, and contact forces. They are somewhat important in explaining what happened but great skiers rarely stop to do all the math in the middle of a good turn. Just sayin...
Bye for now,