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 ] 

 


Intro

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.

Summary of phases

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.

ip2 -  Blend / 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.)

  • Not necessarily push all the way out to full extension to a straight leg.

  • Engaging the big knee-extension muscles requires pushing the skate or ski forward relative to the pushing knee.

ipA - Aim-switch phase

(Switch between in-push and Main-push.)

  • The goal of this phase is to change to aim-angle of the ski or skate relative to the skater's overall direction of forward motion: from aiming toward the other side of the forward direction, to aiming toward the same side as the pushing leg.

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.

Details of each phase

ip0 - Set-down phase for in-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

  • 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.

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.

  • Another way to think of the set-down for in-push is that it's like the second "step" of a cross-over stroke along a curve toward the side of the next leg-push.

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.

  • Foot swings way outside, away from the other foot.

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. ]

  • Knee comes close next to the other knee.

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. ]

  • Foot lands close underneath its hip, on its outside edge.

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.

  • Knee and ankle flexed to bring knee and hip low, with foot landing with heel perhaps behind the hip -- definitely not much in front of the the hip.

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:

  • skate or ski aimed toward the other side (or possibly straight in overall direction of forward motion) -- not at all aimed toward its own side.

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.

  • ankle pronated at landing (or optionally straight in plane of knee-heel-toe).

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.

  • The knee is pointed inward at landing (or optionally might be straight in the hip-heel-foot plane) -- but the knee is definitely not pointed outward.

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.

  • ?? pelvis and hip configuration at at landing ??

  • ?? shoulder configuration at landing ??

  • Ski-skating: Land the ski the minimum edging needed to transmit force to the snow without the ski edge slipping. (see discussion under set-down phase 0 of normal-push.

ip1 - Underneath phase for 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

  • Push out toward the side with the hip adductor muscles.

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.

  • Begin outward-knee-roll move -- (only if knee was previously rolled inward during set-down phase ip0.

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.

  • Ankle-supination move -- (probably best to try this only if ankle was earlier pronated in set-down phase ip0).

"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.

  • Forward-pelvis-rotation move -- opposite hip goes forward.

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.

ip2 - Blend / Extension phase for in-push

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

  • Not push all the way out to full extension to a straight leg.

Actually I have not found any video of any elite racer who goes to full leg extension on the in-push.

  • Engaging the big knee-extension muscles requires pushing the skate or ski forward relative to the pushing knee.

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.

  • ice + ski: presumably if skis or klap-skates are used, there would be an ankle-extension / toe-push move at the end of those phase.

ipA - Aim-switch phase

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.

more . . .

see also

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