by George S. Rossano
(30 December 2019) At the top level, the factors that determine whether a jump attempt will be fully rotated consist of: (1) the time in the air (determined by the height of the jump), (2) the angular momentum at the takeoff (determined by the torque generated during the takeoff and the moment of inertia during the takeoff) and (3) the moment of inertia in the air, controlled and adjusted by the skater during the flight of the jump. For beginning skaters, insufficient height or takeoff angular momentum are common reasons jumps are not fully rotated. For the most difficult jumps (triples and quads), however, it is more often the case that jumps are not fully rotated due to a poor air position that prevents the skater from achieving the rotational speed needed to complete the rotation during the jump. For triple Axel and quads in particular, a nearly perfect air position is required to fully rotate those jumps.
For our discussion here, we define the perfect air position to be that air position that results in the minimum moment of inertia for the human body for rotation about a rotational axis through the long axis of the body.
The perfect air position has the following characteristics (description for a right handed skater).
The following two photographs are the closest we have come to capturing a skater in a perfect air position.
Nathan Chen, 2019 Grand Prix Final, Men's Free Skate
Common errors in air position that increase the moment of inertia above minimum, and slow the rotation, in rough order of decreasing impact, consist of the following:
Items 1 through 4 can significantly increase the moment of inertia of the skater above minimum and render a triple or quad unobtainable. Items 5 through 6 may seem like nitpicking, but it is important to note that small changes in body position can change the moment of inertia by a few percent, and often items 5 through 7 are present at the same time A two percent decrease in the moment inertia during the flight of the jump can increase the rotation of a quad by nearly 30 degrees, enough to turn a barely downgraded call into an under call, or a barely under call into a fully rotated call.
Why is the Perfect Air Position so Difficult to Learn?
Few skaters acquire the skill of a perfect air position, or even a nearly perfect air position. Among those that do, many only hold it for a small fraction of the air time of their jumps. Talking to coaches about this, the following picture emerges, at least for the U.S.
Developmental coaches are under constant pressure from parents who expect to see their children acquire ever more difficult jumps as quickly as possible. A skater does not need a perfect air position to learn singles and doubles, not even double Axel. Once a skater can land a given jump, it’s time to learn the next jump even if the air position is problematic. As long as the skater is advancing up the ladder of jump difficulty, correcting a bad air position has low priority. Parents want to see their child acquire the next jump, not “waste time” making a jump they can do look nicer. If the coach does not focus on teaching the next jump, the parents may take their skaters elsewhere.
The problem with this is that eventually skaters with seriously defective air positions reach a point where their air position prevents acquiring the next most difficult jump. At that point to make progress the air position must be corrected; but by that time it is too late. By the time the skater gets to triples they may have been skating for over six years and their defective air position is firmly ingrained in their muscle memory.
Even without the pressure of parents, for most skaters, if they are making progress learning new jumps, they don’t seem to give high priority to acquiring a perfect air position, until it is too late.
Fixing bad jump technique is very difficult and time consuming. Over the years, I have heard many an elite coach say that if a skater comes to them with bad jump technique it takes a year to unlearn the bad technique and a year to re-learn good technique. Skaters no longer have that time to waste in their development timeline. Skaters starting at age 5-6 must have all their triples by age 14 if they want to be champions. In today’s world of competitive skating, skaters who do not work on acquiring the prefect air position from the beginning are unlikely to ever acquire that skill.
For the Judges this Used to Be a Big Deal
In the 6.0 system, prior to Midori Ito, a bad air position in the form of a “wrap” was killed in the scoring, even if the skater landed the jump. Once Ito started landing triple Axel with a wrap, however, suddenly the wrap went from a serious error of technique to an acceptable “alternate” technique.
Under IJS rules, a poor air position is subject to a GoE reduction of -1 to -3, yet (looking at protocols) few judges seem to actually take this reduction. Like everything else in skating, if judges do not mark down a defective air position, there is little motivation for skaters, parents or coaches to do anything about it, if they are landing the jump and getting positive GoEs. When it comes to poor air positions, the motivation and moral support judges used to provide developmental coaches (through the marks) to instill good technique seems to be lacking today.
For Moment of Inertia Cloths Matter Too
Basically, when it comes to moment of inertia the skater should perform naked, and after that in a light weight body stocking. Those choices being impractical and violations of the rules, realistic costumes with the lowest contribution to moment of inertia are tight fitting unitards for the ladies, and tight fitting trousers and a not too blousy shirt for the men, in both cases not weighed down by the addition of stones or superfluous heavy costume elements.
Costume elements that flair away from the body during rotation have the biggest impact on increasing the moment of inertia, and adding stones to these elements makes the situation worse. Stones on the torso have the least impact, while stones on the arms and legs more. An injudiciously designed costume can increase the moment of inertia by as much as 10%. To compensate for this, the skater would have to jump 20% higher, or take off with an additional 10% angular momentum. Otherwise the skater will lose 10% of the rotation otherwise achievable without the impediment of the costume (four-tenths of a rotation for quads).
This discussion for singles skating is as applicable to throws and twist lifts in pairs as it is to solo jumps, with one exception to be noted. In throws and lifts the woman usually crosses one arm in front of the torso and one behind. In this case, the minimum moment of inertia has the upper arms tight against the sides of the torso and the forearms tight against the abdomen and back, with the palms open and hands flat against the abdomen and back. Achieving a perfect position for the arm in back, however, is limited by the available range of motion at the shoulder when the arm is behind the back, and is difficult to achieve.
(1) Small variations in the positions of the arms and hands against the torso can have equivalent minimum moments of inertia.
(2) For female skaters, placing the hands and/or arm over the girls (once developed) instead of against the torso will increase the moment of inertia above minimum.