what's here
Assumptions + Principles
0 - Set-down phase
1 - Underneath phase
2 - Central push phase
3 - Extension phase
more
see also
Q: But isn't the true limiting factor on skating speed and power
"VO2max" -- the capacity of the athlete's cardio-vascular system to
deliver oxygen?
A: Actually for many athletic performances, the work-level most
of the time is not done at an intensity that reaches VO2max: e.g.
skating a marathon. For performances longer than a few minutes, the
ability for specific "peripheral" muscles to avoid lactic-acid-related
fatigue is the key to not burning out early -- so spreading the power
load to other muscles that are near their lactic-acid "threshold" limit
can be a big help.
But even for short high-intensity situations, it's not simply an
either/or, VO2max versus many-muscles, because V02max is not a fixed
constant. So in training for several months, the more different muscles
getting developed to make an effective contribution to propulsion
implies greater muscle mass available to impose a greater demand for
oxygen during high-intensity short-interval training workouts. Greater
total demand for oxygen puts more stress on the central cardio-vascular
system, which can be a key stimulus for it to grow higher VO2max
capacity.
That's why elite cross-country ski-skate racers often have higher VO2max
than elite bicycle racers: The ski-skate racers do a lot of pushing with
their ski poles using their upper-body muscles, so they're using more
muscle mass than the bicycle racers.
In some actual-race-performance situations (e.g. final sprint), a racer
might choose to channel this increased V02max capacity into a
fewer-muscle-moves technique, while in other actual-race situations the
racer has sufficient V02max capacity to support a many-muscle-moves
technique. That's a choice which training with many-muscle-moves
technique offers.
Q: How come some inline speedskaters almost have both skates in the air
for an instant between strokes?
A: I don't know. My main theory is that some overlap of the phases of
the two legs is good, like overlapping part of Phase 3 of one leg with
Phase 1a (or Phase U1) of the next leg. And in the race videos I've
analyzed, it seems like 10K and marathon skaters usually follow that
theory.
But from looking at some of the 200m and 300m winners at the 2004 inline
World Championships, looks like some of the short-distance short-track
winners (e.g. Gregorio Duggento and Valentina Belloni) do not overlap
their leg-pushes. They even show a little gap in between strokes, with
neither skate fully on the ground. It's still a puzzle for me.
Q: The skater's body tends to fall downward and sideways in phase 3 of
the push. If set-down is delayed, the body has more time to fall further
and faster. Does this help propulsion? Is it a "free lunch" from
gravity?
A: Quick response: My analysis of the physics says: Delay in itself does not help propulsion. Falling
directly downward faster doesn't help. It's not the "fall" part that
helps, it's the sideways. If keep pushing strongly sideways in Phase 3
of other leg so that the sideways speed of the body increases while
Set-down is delayed, that does help propulsion.
It's not a "free lunch": The skater really has to keep pushing with the
obvious leg-extension muscles. If fall farther and faster before
landing, must land with knee and ankle joints more flexed and absorbing
more downward impact -- which puts more strain on the obvious
knee-extension and hip-extension muscles.
Falling farther can be a result of pushing through a longer
range-of-motion of leg-extension (either by starting from a more flexed
configuration, or by finishing in a more extended configuration) -- in
which case, provided that the skater pushed with the same average force
through that range, propulsion will be increased. Or falling farther can
be a result of landing the foot farther out to the side, in which case
(other things being equal) it does not help propulsion.
Playing with the feeling of sideways fall and managing the balance of
delaying the set-down move can be very helpful as mental image and
control sensitivity. But overall gain in propulsion comes only if the
imagery and balance result in the skater actively pushing more.
[ more to be added ]
( ?? Is there a way to allow body to fall downward in phase 3 without
helping propulsion)
Q: How come elite cross-country XC ski racers usually make a
distinct inward-roll-knee move (combined with an ankle-flexion move)
when they skate (i.e. knee goes inside the hip-heel-toe plane)?
While elite inline + ice speedskaters make at most a small
inward-knee-roll move, none? Also ice + inline technique coaching
shows little interest in the ankle-flexion "knee drive" move.
Non-elite skaters are different: Many non-elite XC ski racers
often do not use the ankle-flexion "knee drive" move, and non-elite ice
+ inline speedskaters do make an inward-knee-roll move.
A: I'm not sure why. At first I thought it was because XC ski
racing tends to require lots of high-force situations (hills and soft
snow). But inline skate racers in short distances on a short oval track
are also in high-force situations, and they do not use inward-knee-roll.
Here's some possible explanations I've encountered so far:
(a) Elite cross-country ski racers usually ski "classic striding" style
as well as skating, and classic striding uses the ankle-flexion move
effectively for propulsion, so that muscle set is well-trained for speed
and endurance. The inward-knee-roll move enables them to use that
well-developed muscle-move for propulsion in skating. While inline
speedskaters do not tend to do much "striding" or "running" sports.
(b) Inline and ice speedskating uses the upper body mainly for reactive
side-force, so it's important to achieve maximum transmission of
side-motion of hips and upper body -- and inward-knee-roll move partly
tends to absorb that side motion, or not to create as much of it. While
XC ski racers use their upper body mainly for pole-push force, so a
slight loss of side-motion transmission is less important for them.
(c) Race courses for elite cross-country ski racers have steep hills on
them -- more and steeper than most inline race courses, and most snow is
slower than most pavement on outdoor inline race courses. This requires
that cross-country ski racers aim their skis out much wider in critical
race situations. The inward-knee-roll move combined with ankle-flexion
move is more effective for propulsion when the aim-angle of the ski is
farther toward the side -- because the ankle-flexion muscles naturally
direct their force backward (while the lateral-hip-adductor and
inward-hip-leg-rotation muscles favored by inline racers are not as good
for directing force more backward). Since the inward-knee-roll +
ankle-flexion moves are more successful (and well-trained) for their
most critical situations, cross-country skiers tend to rely on them also
in other situations even where the ski aim-angle is less.
Perhaps some speedskaters in large aim-angle situations: like the start
of a race, use some inward-knee-roll: see Valentina Belloni in her start
in winning the 200-meter time trial in the Inline World Championships
2004.
(d) Perhaps the inward-knee-roll move it has something to do with coming
down from having the body up high to set up for double-poling in
cross-country skiing. In V1 skate, the inward-knee-roll move seems more
noticeable on the poling side than on the recovery side. But sometimes
racers also do it when they're not poling (perhaps out of habit?).
Q: Ice and inline skaters when doing normal-push stroking usually land
with their foot tilted toward the outside, then "roll it over" during
Phase 1 so that the foot is then tilted toward the inside. Is this "roll
over" propulsive? Is it a pre-requisite "trigger" for propulsion?
A: Quick response:
[ ski: ] On skis, roll-over is important in the
physics because the ski cannot transmit propulsive force effectively
while its running flat, not tilted toward one side of the other, and
perhaps there are frictional costs or control risks if try to do the
roll-over while also trying to apply significant propulsive push through
the ski. So expert ski-skaters tend to just avoid the roll-over by
landing the ski alreadly tilted slightly toward the inside (or perhaps
land it flat).
[ inline: ] For inline speedskaters, whether the
foot or boot or wheel-frame is tilted slightly to one side or to the
other or standing straight vertical has no significance in the physics
of propulsion or control. So for inlines "roll-over" is important only
as a mental image.
What matters for propulsion during roll-over is the four muscle moves
described in Phase 1. If the mental image of "roll-over" helps the
skater engage and develop those muscle moves, then it's positive. If it
gets the skater not to do any effective pushing until after the foot is
tilted toward the inside, then the mental image of roll-over is negative
for propulsion.
The key pre-requisite "trigger" for propulsion in Phase 2 is getting the
foot out toward the side far enough away from hip, so that there's large
enough vertical leg-slant angle to that extending the leg also has a
substantial non-vertical component. As long as the foot is near to
underneath the hip, most of the force of any push by the big obvious
hip-extension and knee-extension muscles will just go straight into the
ground, not into pushing the skater forward (or even sideways). The
skate or ski can be tilted toward the inside after roll-over as long as
anybody desires and can manage the balance, but Phase 2 cannot begin
effectively until the foot gets further out to the side. Roll-over is
not sufficient.
[ ice: ] The ice skate blade is not as effective
for transmitting propulsive force while running flat on the ice, and
perhaps there is some control risk during the moment of roll-over. But
the ice skate blade can transmit substantial propulsive force through
the outside edge of the blade, so there is no benefit to wait until
after roll-over to start applying force through it (perhaps think of
"pulling" on the blade toward the outside).
So on ice it could be valuable to get through the "running flat"
configuration more quickly -- one trick is to use an ankle-pronation
move. And of course learn to feel how to best apply how much force
through the blade in each configuration before, during, and after the
roll-over point. Otherwise the physics is much like for inlines.
[ double-push: ] The physics of the Aim-switch in
double-push is a bit different from roll-over in normal-push. See
analysis of the Aim-switch
phase A.
[ no questions yet ]
Q: How come elite racers don't make all the moves available for maximum
extension of the leg?
Especially glaring is that they often end their normal leg-push with the
ankle in a pronated position (bent downward and inward from the
hip-heel-toe plane). If they made an ankle-supination move in Phase 3,
they could properly straighten their leg, so it would push their heel
farther out from their hip, and also push their foot out along the
surface of the ground.
Another possibility is that they could get more difference in
hip-to-heel distance if they made a combined inward-hip-leg-rotation +
ankle-flex move in Phase 1, and then a out-ward-hip-leg-rotation move in
Phase 3.
A: There's more to propulsion than going through a "range of motion". I
also have to push effectively through the motion. (physical Work
= Force * Distance). Adding to my range-of-motion in some direction is
only helpful if I have some muscle in a configuration to apply a
significant force through that extra range.
If my ankle is pronated after Phases 1 and 2, then an ankle-supination
move in Phase 3 will move my heel further from my hip. Unfortunately the
force through my foot to the ground from that ankle-supination move is
inward and downward. But the propulsive force direction for the
Main-push in normal skating is outward, not inward. (Same problem with the
outward-hip-leg-rotation move).
How about if we combine the ankle-supination move with a hip-abduction
move -- since a hip abduction move in a Phase 3 configuration has an
outward and upward component. But hip-abduction has little effective
power out that far, and the bad upward component keeps getting worse the
further it goes out: it reduces the downforce needed to make the ski or
skate grip against the ground, instead of skidding out to the side.
Q: The skater's body naturally tends to fall downward in phase 3 of the
push. Does this help propulsion? Is it a "free lunch" from gravity?
A: Quick response: Actually it's slowing the fall and stopping it
which can help propulsion -- and starting the (eventually-required) rise
upward again. But starting the fall (and stopping the rise upward)
actually reduces the effectiveness of other pushing and exactly cancels
the benefit of slowing the "natural" fall, for an overall net zero
impact on propulsion.
Any benefit from this "natural" fall is not a "free lunch", since
slowing and stopping the fall takes real muscular work, mostly down with
the obvious big leg muscles.
It's also possible to have an "un-natural" fall (and eventually-required
rise) of mass of only the upper torso and head, by using the
back-extension muscles to handle the required rise. This still require
accurate timing coordination to achieve any overall non-self-cancelling
propulsion benefit.
Playing with the feeling of sideways fall and managing the balance of
delaying the set-down move can be very helpful as mental image and
control sensitivity. But overall gain in propulsion comes only if the
imagery and balance result in the skater actively pushing more.
[ more to be added ]
back to Top | Leg
motion | more Motion techniques
| FAQ
| Resources | more
Skate
|
