what's here
Double-push Phases ip0, ip1, ip3, and ipA replace Phase
0 of the Normal-push sequence of phases.
see also
[ under construction ]
This is a detailed analysis of the sequence of moves for the
"in-push" phases of the "double push" technique of skating
propulsion. These "in-push" phases are only part of the full skating
stroke-cycle. The remaining phases of the double-push technique are
virtually the same as for normal-push skating, so those phases
are on a separate page.
For more context on this analysis, see the
main page for skating Leg motions.
what is it?
For a brief explanation of
double-push
versus
normal-push stroking, see the
Definitions page.
There are (at least) two styles of double-push stroking: "big" and
"lite" -- for an explanation see the
Definitions
page.
equipment differences
In ski-skating the Aim-switch phase
ipA
move can only be executed (reliably and without excessive friction) with
an unweighting of the ski up off the snow. So on skis, double-push
technique is only going to be attempted by very athletic ski-skaters.
Even then it's debatable if there's a net gain in propulsive power, and
in what situations it could be effective on skis.
Perhaps the most likely situation where
double-push could give advantage on skis would be with an icy surface on
flat terrain.
On inline skates there's no problem with the Aim-switch phase, and
double-push technique is widely used by expert speedskaters in various
situations. There's no doubt that when competently performed on inline
skates, double-push technique delivers significant gain in speed. No one
would have a hope of winning an inline 10K or inline marathon race
without using double-push technique.
On ice, the double-push technique is not used much by ice
speedskaters (as of March 2005). My own experience is that double-push
technique is straightforward to perform on ice skates with rockered
blades (such as my hockey skates).
I have not tried ice speedskating, but I've
heard that it can also be done on short-course speedskates, but that
double-push is more difficult on long-course ice speedskates, and only
effective at very high speeds.
ip0 - Set-down phase for in-push
-
Set-down path and Landing configuration are
significantly different from the Normal-push set-down.
-
Timing: Set down the next foot before the
previous leg-push finishes pushing, to minimize any "dead spot" gap
in the stroke-cycle, and to support the push of the other foot.
-
The set-down move can do actual propulsive work in itself
-- not just preparation for work in other phases.
ip1 - Underneath phase for in-push
(Sometimes the in-push is so short that
this phase is almost completely overlapped with phase U3)
-
Hip-adduction move is propulsive already while the
foot is still underneath the hip.
-
Ankle-supination move is effective and propulsive,
if prepared for by setting down in a ankle-pronated configuration.
-
Forward-hip-rotation move can start here.
ip3 - Extension phase for in-push
(No time for a central phase 2 like in
Normal-push, so the hip-extension and other extension moves just get
blended together into a single phase.)
ipA - Aim-switch phase
(Switch between in-push and Main-push.)
Usually the angle to the other (in-push)
side is less than the angle to the same (Main-push) side. Sometimes
the angle to the other side is very small, or perhaps even zero, so the
in-push phases are performed with the ski or skate aimed virtually
straight in the skater's forward direction. In this case the in-push
phases are propulsively generating only reactive side-force energy which
will transmitted to the ground in later phases (and do not help increase
or maintain speed in the current phases).
-
The key point is to get through this phase quickly
and without bad side-effects.
-
Outward-knee-roll move and ankle-supination moves
are not significantly propulsive in this phase A, but can put the
leg in a configuration for greater propulsion work in phase 1 of the
Main-push.
The Set-down phase starts when the knee and
foot have reached their farthest inward position while from their
recovery move in the air. It ends when the foot lands down on the
ground.
If the Recovery move did not move the knee and
foot further inward or backward than the landing point, then the distance and time
of the set-down are very short, nearly zero. But in many situations the
elite racers first move their knee and foot further inward, so the
set-down move has an outward component, and persists through a noticeable
time and distance.
muscle moves
for forward propulsion:
details + hints
Even if the next foot is not visible pushing
yet, just having it on the ground and trying to hold its position
relative to the other foot is already adding force to Phase 3 of the
other foot's push. The force needed to "try to hold" the next foot (net
of some across-the-body transmission losses) is added to the pushing
force through the other foot.
Another way to look at it is that having the
next foot down already gives the other foot something to push against.
If the next foot were not on the ground, more of the work of the other
foot would be going into moving the mass of the upper body faster
sideways, instead of immediately propulsive. The faster sideways motion
can be converted into propulsion is future phase, but there is some
power lost in that conversion.
Another advantage of double-push over
normal-push stroking is that the aim-angles of the two feet
during the period of overlap is closer (because they're both aimed to
the same side), so more force can be transmitted for a longer period
between the two feet, especially at high speeds. If the feet are aimed
further apart while they're both on the ground, then they "split" apart
much quicker for the same amount of force between them.
Think of the position at the end of the
Recovery phase as like just having lifted the second foot after
completing the first step (the main "cross over") of a cross-over
stroke. Then phase ip0 is like the cross-over second foot set-down, and
phases U1 and U3 are like the cross-over second push on a curve toward
the side of the in-pushing leg (toward the outside of the curve,
which is toward the inside of the in-pushing leg). But then instead
of starting the first step of the next cross-over stroke to keep
curving, pivot and push the other way to send the body toward moving
straight ahead forward.
- Foot is started back outward sideways a little just before the
foot lands.
To generate beneficial reactive side-force in
acceleration.
Benefits from this move:
(a) adds range-of-motion to the inward push of
phases U1 and U3.
(b) adds reactive side-force propulsion of
acceleration.
The main muscle move which does this is the
inward-hip-leg-rotation [
see more ].
[ Normal-push is different. ]
Makes it easy to aim the knee inward, with two
main benefits -- see below under aim knee inward.
Some skate teachers say "the knees kiss".
[ Normal-push is different. ]
If land the foot way across the centerline on
the other side, miss out on much of the range-of-motion for the
hip-extension move -- perhaps the biggest propulsive muscle move
available.
Normally inline speedskaters doing double-push
land the foot a bit inside its hip. Not clear to me if this is just an
old tradition from normal-push skating. Seems like could get more
range-of-motion in the in-push if landed the foot directly underneath
its hip, or even a bit outside its hip. But perhaps the biomechanics do
not allow much inward-pushing force to be applied from that
configuration.
To prepare for maximum propulsive
range-of-motion for knee-extension move in phase U3.
[ for the Main-push, the landing could be
more forward, because the ankle-flexion move in Phase 1b will bring the
knee forward and the heel back. But in the shorter in-push stroke
there isn't time for much of that.
Landing configuration is different from the Normal-push
set-down:
Not aiming toward the same side as the pushing
leg is the fundamental hallmark of the in-push.
What is suprising is that the in-push can
also add propulsion if it is landed aiming virtually straight in the
direction of the skater's overall forward motion -- a configuration
often seen in inline marathon races, especially for climbing up a
non-steep hill.
Landing with ankle pronated prepares for
maximum propulsive range-of-motion in ankle-supination move on phase U1.
Delay any ankle-supination move until after landing.
Benefits from pointing the knee inward:
(a) Makes it easier to aim the ski or skate
more inward and more away from straight forward. This aims more of the
in-push force into immediate propulsion through more direct push
backwards, rather than delayed reactive side-force transmitted to future
phases.
(b) Configures the knee and ankle for an
outward-knee-roll move in the in-push.
Sometimes the in-push is so short that this
phase U1 is almost completely overlapped with phase U3.
This phase goes from the landing of the foot
until (roughly) the completion of any ankle-supination move and start of the
knee-extension move.
muscle moves
for forward propulsion:
details + hints
These muscles are not large, but every little
bit helps -- to take load off the obvious big leg muscles.
Or if the other leg is still pushing into the
surface, and there is overlap of the final phase of the previous
leg-push with this initial phase of the next leg-push, then just holding this
hip stable ("isometric") can provide a "fixed point" for the
other leg to push
against -- which adds to the effective force transmitted to the
snow.
This "outward knee roll" move pushes the
foot a
little ways in and back, and the upper body a little further out toward
the other side and forward. So
it adds to forward-propulsion power. Not much, but every little bit
helps -- to take load off the obvious big leg muscles.
"supination" = bending the ankle joint sideways
toward the outside of the knee-heel-toe plane, so the sole of the foot
turns away from more outward and toward facing more inward.
Setting down in phase ip0 with the ankle
already in a somewhat pronated position enables a larger positive-propulsion
range-of-motion for the ankle-supination move.
[ ski: for ski-skating on
snow, landing with ankle already pronated is not usually going to fit with the need to
make the in-push through the outside edge. So usually the best that ski-skaters can work on is trying
minimize the supination at set-down in phase ip0. ]
The problem with supination if the ankle lands
straight is that bending to too large an angle of supination
could result in more negative work than positive -- because it also
shortens the overall leg-length. Simplest to just stop the move when the
ankle comes to a straight configuration (in the knee-heel-toe plane).
?? Possibly could supinate beyond straight in
Phase U1 and then pronate back to straight full extension in Phase U3 --
?? just the opposite of the pronation / supination pairing in Phases 1 and
3 of the Main-push. But this seems pretty tricky to execute given the
shortness of the in-push phase.
This move rotates the hips and pelvis about
the vertical axis -- so the hip joint of the next-pushing leg comes
forward -- and the hips and pelvis turn away from facing toward the
next-pushing side, and turn to face toward the current leg-push side.
This has several interesting helpful results:
- - uses muscles in the abdomen and
lower back (likely including the "obliques") to apply forward-propulsion
work by moving the mass of the next-pushing leg and hip and side of the
torso forward against air resistance (also gravity if going up a hill).
- - advances the next foot forward, but
without "stepping" it forward. The problem with "stepping" the foot
forward is that its hip joint gets left behind, which then requires the
hip-extension muscles to operate in a less favorable segment of their
range-of-motion in the next leg-push. Instead the forward-hip-rotation
move advances the hip and foot together.
This phase goes from (roughly) the start of the knee-extension move. There may be some overlap with
phase U1, and with phase A.
muscle moves
for forward propulsion:
- hip extension - [
see more ]
- knee extension - [
see more ]
- forward hip rotation - [
see more
]
- (only for skis or klap-skates): ankle
extension
details + hints
Actually I have not found any video of any
elite racer who goes to full leg extension on the in-push.
The "magic" of skating is that it's possible
to generate a backward push-force by pushing out toward the side on a
skate or ski that is slicing forward. See discussion and links under
Phase 3 on
Normal-push page.
This phase goes from (roughly) the finish of the
hip-extension and knee-extension (and any ankle-extension) moves of the
in-push, until the skate or ski as in an aim-angle and
edging-weighting-configuration where it can transmit force into the
ground through Main-push.
The key change is that
-
before the Aim-switch move, the skate or ski can
transmit forces into the ground in the direction sideways away from
this pushing leg (and perhaps also transmit force in the backward
direction)
-
after the Aim-switch move, the skate or ski can
transmit forces into the ground in the direction sideways toward
this pushing leg, and definitely also transmit force in the backward
direction.
muscle moves
no propulsive moves.
But this Aim-switch phase can be used to dissipate
counter-productive forces in a configuration where there are less
negative.
details + hints
-
The key point is to get through this phase quickly
and without bad side-effects.
-
Ski-skating: Usually the effective way to make this
substantial change in the angle of the ski is to hop up into the air
-- because the ski is so long and the snow has large resistance and
friction against pivoting moves.
Unless it's icy, in which case pivoting might
work.
-
Inline: The Aim-switch move is straightforward to
make by pivoting or steering the skate.
-
Outward-knee-roll and ankle-supination moves are
not significantly propulsive in this phase ipA, but they can put the
leg in a configuration for greater propulsion work in phase 1 of the
Main-push. See discussion of Normal-push
Set-down phase 0
for more ideas on how this phase can prepare for future phases.
see also
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