Quadruple jumps combine a complex array of kinetic forces: horizontal as the skater builds up speed for the jump; vertical, as they launch into the jump; and rotational as they revolve as quickly as possible. Timing has to be perfect.
Kevin Reynolds takes about three-quarters of the ice surface to build up speed for the quad. Sports scientists estimate that while skaters can move at more than 32 kilometres an hour around the ice, they slow down for a quadruple jump, to 19 km/h at the moment they stick their toe picks into the ice (if they are doing a quadruple toe loop).
But the more proficient they are with a jump, the quicker they can go into it.
Reynolds says he travels at 100 per cent of his top speed going into his quadruple toe loop, 80 per cent going into the quadruple Salchow and 60 to 70 per cent for his quad loop, his newest quad.
IN THE AIR
Skaters launch themselves into the air by pushing against the ice to go upward, at about a 40-degree angle off the ice with a force that is four times their body weight. Christy Krall, coach of Patrick Chan, says a skater needs to get 21 inches off the ice to have time to get the rotations in. Chan's quads are 22½ to 23 inches off the ice. Reynolds says he doesn't jump as high as some, but he rotates quicker than some.
Once in the air, skaters have to achieve their first tight position at time of takeoff, within 0.08 of a second. They rotate from 4½ to six times a second. Quick rotations are essential: a quad lasts for only 0.650 to 0.750 of a second.
At the apex of the jump, skaters are doing their third rotation, with one more to go before they land. But the key to doing a quad is snapping the arms and legs into position as tightly and quickly as possible. An elbow, a head or a free leg that sticks out will slow down rotation. "You want to be as thin as possible, almost as though you were a pencil," Reynolds says.
It's not easy to be narrow. Centrifugal forces require skaters to pull their limbs in at a force 1½ times their body weight, according to Ithaca College (N.Y.) sports scientist Deborah King. Krall says the rotation constitutes 200 pounds of centrifugal force per square inch on the body. Reynolds weighs 130 pounds soaking wet.
BACK TO EARTH
Skaters do the rotations with a slight backward tilt, which is essential to landing in balance. If they do the rotations perfectly vertically, they will come down on the heel of their blade - and land on their butts.
When a skater prepares to land the jump and slow the rotation, the free leg and the arms come out, and they land on the backward edge of a blade that is only one-eighth of an inch thick.
When they land, they generate a force seven times their body weight.
When it's landed well, it feels soft and natural. But if a skater's weight has shifted ever so slightly, the foot will come down with a thud.
"It requires an enormous amount of core strength and focus to have the exact timing to break out of the rotation you've created," Reynolds said.
By comparison, when a person jogs, they land with 2½ times their body weight on each foot. In other jumping sports such as volleyball or basketball, athletes land with a force not higher than three or four times their body weight.
It's no wonder skaters limit the number of quads they do in practice.