what's here

   Set-down for inward leg-push

   Max-In-Push (Front view)

   Finish of In-push (Side view)

   Crossing from inside to outside (Front view)

more . . .

 

  

[ under construction ] 

 


Set-down for inward leg-push

 

see the Double-push sections on the Set-down observations page

also the Double-push section in the topic of overall Timing sychronization.

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front view at Max In-push

checkpoint:  "Max In-push" = The frame in Front view that shows maximum inside reach by the foot in inward leg-push.

see more on Definitions

This is the frame where the foot is aiming straight in the skater's overall direction of forward motion -- which should be straight into the camera, if this is truly a Front view.

The tricky question is, "How much of the inside move from Set-down to Max In-push was just steering the foot into an arc and gliding passively -- versus active pushing to the inside -- with transmission of the push to the mass of the upper body?".  See more below.

ground contact to hip relationship

priority: B  

standard-form perceptual check

Foot crossed over to the inside to vertically underneath the other hip (which just finished it's main outward push).

Pushing hip should be at least as high off the ground as it was at Set-down.

Extension In-push

Foot should be crossed over to the inside to at least as far as vertically underneath the other hip.

Sometimes very strong skaters lean over even further to the outside, so the foot is farther inside than the other hip.

Pushing hip should be higher off the ground than it was at Set-down.

Sweep sideways focus

Foot should be significantly crossed over to the inside from underneath its own hip -- at least half-way across to vertically underneath the other hip. How far depends on the strength of the skater's In-Sweep muscles (hip-adduction, etc.) and on the skating situation (usually crossing less when going up a hill or into a headwind).

Straight only in-push

Foot should be somewhat crossed over to the inside from underneath its own hip. 

knee - ankle - ground relationship

priority:  B-

"neutral" = ankle joint in line between ground-contact and knee joint.

It adds some propulsive work if the ankle is somewhat "supinated" (ankle joint outside the line from ground-contact to knee joint).

This is good provided that: (a) the ankle was not already supinated at Set-down; and (b) the force is transmitted through the knee (see ankle-knee-hip) and hip into the mass of the upper body (see relative sideways stability); and (c) other muscles have not reduced their (unconsciously?) their sideways force or range-of-motion in order to allow ankle-supination to have enough force remaining to show some positive motion.

If an ankle-supination move is to be made, a higher proportion of its force goes into propulsion if it is performed earlier after Set-down than later.

Bad at this checkpoint is if the ankle is pronated (ankle joint outside the line from ground-contact to knee joint) -- since that is a failure to transmit propulsive force from leg muscles and upper body to the ground.

The ankle is a critical point for transmitting In-Sweep forces from the upper leg and upper body to the ground. Doing a good job in this "stable transmission" role is more important than having the ankle try to add work from its own motion -- so it does not help if other muscles reduce (unconsciously?) their sideways force or range-of-motion in order to allow ankle-supination to show some positive motion.

Skilled inline speedskaters usually show a "neutral" configuration, but some of the fastest show some ankle-supination.

ankle - knee - hip relationship (front)

priority: C 

"neutral" = knee joint in line between ankle joint and hip joint.

It adds some propulsive work if there has been some "lateral knee-hip rotation" (knee joint outside the line from ankle joint to hip joint).

"medial" hip rotation moves the kneecap toward the inside toward the other leg.

"lateral" hip rotation moves the kneecap toward the outside away from the other leg.

This is good provided that: (a) the leg was not already in a "lateral knee-hip rotation" configuration at Set-down; and (b) the force is transmitted through the hip into the mass of the upper body (see relative sideways stability); and (c) other muscles have not reduced their (unconsciously?) their sideways force or range-of-motion in order to allow the muscles for this move to have enough force remaining to show some positive motion.

Lateral knee-hip rotation is not compatible with full extension of the leg -- and the usually the  leg is not fully extended in the inward push -- so it could make sense to use lateral knee-hip rotation to add propulsive Work to the inward push of Double-push. But I've never seen it in a video.

If a "lateral knee-hip rotation" move is to be made, a higher proportion of its force goes into propulsion if it is performed earlier after Set-down than later.

If a "lateral knee-hip rotation" configuration is observed, it is important to check carefully for stability in hip-adduction and the upper body -- for details see relative sideways stability.

I have not yet observed lateral knee-hip rotation in any video of a speedskater.

Even  though it seems like it makes sense from the physics, and that it is compatible with the knee being in a flexion configuration.

It would make sense for lateral knee-hip rotation to be used especially with the "sweep sideways focus" and "straight only in-push" styles of Double-push, because those are emphasizing more the In-Sweep moves, and getting less help from Extension moves.

relative sideways motions + stability

Priority:  A

No "wiggly" in the motion between Set-down and Max In-push:  Every joint and body part moves at least as far sideways outward as the joint immediately below it.

This is one of the critical differences between just tracing "S curve" arcs and really making a new effective kind of push.

Basically this is same observation as in the

relative sideways motions + stability on the Midway page

but in the opposite direction. So see that discussion, but

  • une "inward" in place of "outward" (and vice versa)

  • use hip-adduction in place of hip-abduction

  • use "lateral knee-hip rotation" in place of "medial knee-hip rotation"

  • use ankle-supination in place of ankle-pronation

pelvis hips side-tilt

priority: B

See discussion of different approaches to this move on Finish page.

Pelvis should be tilted sideways away from the leg-push (or level). Since this In-push is pushing toward the inside, the pelvis should tilt toward the outside.  Hip of the pushing leg should be lower than the other hip being set down.

Or for those who believe in keeping hips level at all times, OK then keep them level.

But the pushing hip at its Finish should definitely not be higher than the other hip as the In-push is finishing.

hip - torso-shoulder relationship

priority: B  (or A)

This is a priority B if the question is between gaining power from a torso-shoulder side-swing move or not gaining. It's priority A if the skater is actually losing power due to mis-timing of torso-shoulder motion.

Typical problem in Double-push is starting the torso side-swing move too early, and failing to gain power from it -- but not actually losing power.

Position of shoulders should be roughly centered over hips (or perhaps somewhat toward the outside) -- and moving quickly (relative to the hips) across to the side of the main push outward, moving from outside toward inside.

Except for those believing in the "quiet upper body" style.

Typical problem seen with Double-push is that the shoulders have already reached a position over on the inside.

hand - arm - shoulder relationship

priority: C

This is priority C if the question is between gaining power from an arm-swing move or not gaining. It's priority B if the skater is actually losing power due to mis-timing of arm-swing motion.

view:  best observed in front view, not foot-aim view. 

If arm-swing is not being used to add propulsive Power, then this observation can be whatever fits with or helps other aspects of the skater's motion -- e.g. balance or rhythm.

If swinging the arms and hands from side to side is being used to add propulsive Power, then the observations should be like for the position and motion of torso + shoulders under hips - torso-shoulder relationship -- e.g. for simple Normal-push, arms roughly in front of body, perhaps a little to one side -- but not way off to one side or the other, and moving definitely toward the set-down side.

If swinging the arms and hands forward and backward is being used to add propulsive Power, then the observations should be different from that.

recovering leg

priority:  C-

You'd have to work at it to get this observation wrong at this checkpoint.

In front view, the foot of the recovering leg in the air should still be further inside than the foot on the ground -- but definitely moving away from the inside and toward the outside.

The way to get this move wrong would be to hold the recovering leg toward the inside while up in the air, and not to let it start moving toward the outside until the foot is pointed straight forward.

Or to get it really wrong:  Not let it start moving toward the outside until after the other foot is angled toward the outside. But that is difficult.

A way to get it a little wrong would be to exaggerate the backward aspect of leg-recovery and neglect the sideways aspect just after lifting the foot off the ground.

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side view at Finish of In-push

checkpoint:  The finish of the inward push. The frame in Side view when the foot is farthest forward relative to its hip.

see more on Definitions

Key differences between the inward push and the outward push:

  • the hip is usually falling at the end of the outward push -- not at end of inward push.

  • heel often comes up at the end of outward push -- not at end of inward push.

toe - ankle - knee relationship

priority:  A

standard-form perceptual check

toe - ball and heel all at down at the same distance from the ground -- no lifting of the heel.

knee-to-ankle line perpendicular to the ground surface.

Extension In-push

toe - ball and heel all at down at the same distance from the ground -- no lifting of the heel.

knee-to-ankle line perpendicular to the ground surface.

Sweep sideways focus

toe - ball and heel all at down at the same distance from the ground -- no lifting of the heel.

toe-ankle-knee angle is not very important for this strategy -- likely less than 90 degrees is good.

Straight only in-push

toe - ball and heel all at down at the same distance from the ground -- no lifting of the heel.

toe-ankle-knee angle is not very important for this strategy -- likely less than 90 degrees is good.

ankle - knee - hip relationship (side)

priority:  A

The knee joint does not go to full extension at finish of the inward push. (unlike the outward main-push). So the knee joint should not be real close to the line between the hip and the ankle.

standard-form perceptual check

The line from hip to knee should be about 25 degrees away from vertical.

The knee joint should definitely be in front of the line between the hip and the ankle.

Extension In-push

The line from hip to knee should be about 20-25 degrees away from vertical.

The knee joint should definitely be in front of the line between the hip and the ankle.

Distance between hip and ankle should have definitely increased since Set-down.

Sweep sideways focus

The ankle - knee - hip angle is not that important for this approach. If using a "lateral knee-hip rotation" move for Sweep-in force, then having the knee more bent is helpful.

Straight only in-push

The ankle - knee - hip angle is not that important for this approach. If using a "lateral knee-hip rotation" move for Sweep-in force, then having the knee more bent is helpful.

pelvis hip rotation

priority: C

Rotation of the pelvis about the axis of the spine is one determiner of the "gearing" of skating.  See discussion on Set-down page.

Having the pushing hip somewhat behind the other hip (or the recovering leg) at this point is good for adding power in lower-force / higher-speed situations -- which often holds for double-push. But for doing Double-push up a moderate (or steep) hill, having the hips even could be good. 

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front view of Crossing

checkpoint:  Crossing = The frame in Front view when the foot passes vertically under its pushing hip.

see more on Definitions

The tricky question is, "When does active pushing outward start?" -- versus just steering the foot and gliding passively.  See discussion on the Midway page.

 

Foot aiming angle.

Timing of Torso-Swing and Arm-Swing

 

hip is definitely higher than it would be at Set-down in this position for Normal-push stroking.

 

?? [ more to be added ]

 

The knee and ankle joints flex during this time.

the pushing hip drops continually lower to the ground.

But I do not think the knee and ankle get as flexed as they do in Normal-push stroking.

 

foot aiming angle

If this observation is off, it would be a sign that something else is really off.

Extension In-push

Foot should be aimed strongly toward the outside, already at the angle of its main Extension push in the outward direction.

Sweep sideways focus

Foot should be aimed strongly toward the outside, already at the angle of its main Extension push in the outward direction.

Straight only in-push

the Crossing checkpoint is not relevant to this strategy, because it's pretty much the same as the Set-down and Max In-push checkpoints.

hip - torso-shoulder relationship

priority: B  (or A)

This is a priority B if the question is between gaining power from a torso-shoulder side-swing move or not gaining. It's priority A if the skater is actually losing power due to mis-timing of torso-shoulder motion.

Position of shoulders should be over toward the outside -- and perhaps still moving somewhat toward the outside.

Except for those believing in the "quiet upper body" style.

Typical problem seen with Double-push is that the shoulders have already started moving toward the inside.

hand - arm - shoulder relationship

priority: C

This is priority C if the question is between gaining power from an arm-swing move or not gaining. It's priority B if the skater is actually losing power due to mis-timing of arm-swing motion.

view:  best observed in front view, not foot-aim view. 

If arm-swing is not being used to add propulsive Power, then this observation can be whatever fits with or helps other aspects of the skater's motion -- e.g. balance or rhythm.

If swinging the arms and hands from side to side is being used to add propulsive Power, then the observations should be like for the position and motion of torso + shoulders under hips - torso-shoulder relationship -- e.g. for simple Normal-push, arms roughly in front of body, perhaps a little to one side -- but not way off to one side or the other, and moving definitely toward the set-down side.

If swinging the arms and hands forward and backward is being used to add propulsive Power, then the observations should be different from that.

recovering leg

priority:  B-

In front view, the foot of the recovering leg in the air be roughly at its farthest distance inward from it hip -- or perhaps still moving inward.

If the foot reached its farthest inward distance in the air significantly before this Crossing checkpoint, then likely part of the opportunity for propulsive Work was lost.

It requires a quick sharp acceleration sideways after lift-up to give the foot and leg enough momentum so that it's still moving inward at the time of the other foot's Crossing checkpoint.

The key determiner in the physics of added propulsive Work from the leg-recovery move is the sideways speed the recovering foot is still carrying when the foot on the ground starts aiming substantially toward the outside. How far a distance the recovering  foot moves sideways is not directly relevant -- except as visible evidence of the sideways momentum.

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more . . .

active push versus passive glide

How much of the inside move from Set-down to Max In-push is just steering the foot into an arc and gliding passively -- versus active pushing to the inside -- with transmission of the push to the mass of the upper body?.  How observe that accurately in video?  Basically this is same question as in the

active push versus passive glide discussion on the Midway page

but in the opposite direction. So see that discussion, but

  • une "inward" in place of "outward" (and vice versa)

  • use hip-adduction in place of hip-abduction

  • use lateral knee-hip rotation in place of medial knee-hip rotation

  • use ankle-supination in place of ankle-pronation