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ski-skating alternatives

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intro

This is one phase in a detailed analysis of the sequence of moves for Leg-push motions of "normal  push" method of skating. For more context and an overview of all the phases of the sequence, see the summary of normal-push phases.

There is an alternate set of moves for this phase, often used by ski-skaters -- see below.

key points

  • Theme: Catch side-weight-shift energy from previous phases and transmit it into current push-force through the foot. Start pushing already with Side-of-leg-Out moves. Find a trick to get through low-power phase 1b quicker.

  • Maximum transmission of side-weight-shift energy into the foot: No absorption or collapse.

Effective transmission uses the same Side-of-leg-Out muscles (and Forward-abdomen-rotation and Torso-swing muscles), but in "eccentric" and/or "isometric" modes.

One absorption "trap" is to allow the hip to go outward relative to the knee, instead of stabilizing the hip-knee configuration with the lateral-hip-abduction muscles.

  • The time just after the foot lands does not have to be "passive glide". The leg can already start doing actual propulsive work by using Side-of-leg-Out moves.

  • Ankle-flexion move (if not already complete in Set-down phase 0) prepares for Extension moves in future phases -- by moving the ankle joint way back behind the knee, which "aims" the knee-extension push so it can help the Extension push out toward the side. It also adds range-of-motion to the ankle-extension push.

  • Hold back on leg Extension moves.

In this phase they are "aimed" mainly to raise the hip upward (and this vertical potential energy is inefficiently converted into later propulsion except for a skier using a pole-push). The Extension moves will be more effectively "aimed" for propulsion starting in phase 2 and more so in phase 3, when the leg-lean angle is larger. (Then the hip will get raised up plenty.)

  • Phase 1b is the low-power segment of the stroke-cycle. To increase overall average power, find a way to get through phase 1b quicker.

[ inline + ice-rocker-blade ] Skaters can get to a phase 2 leg-configuration quicker by aiming the skate out further to the side during phase 1b, then pivoting it during phase 2 to aim move forward during phase 3.

definition of this phase

??

This phase goes from the landing of the foot on the ground until (roughly) the completion of the "non-extension" side-push moves (tranverse-hip-abduction, inward-hip-leg-rotation, ankle-pronation) and (roughly) the start of the hip-extension move. But there is likely significant overlap between phase 1 and phase 2, so perhaps it's more a shift in focus between the two, rather than some well-defined "trigger".

The themes of this phase are:

  • Transmit the sideways-directed kinetic energy from the previous leg-push.

  • Initiate pushing sideways (and partly backward) from underneath (or almost underneath) the hip of the pushing leg (which starts roughly vertical). This push is "contractive" in that three out of four of the moves have the effect of shortening the distance between the foot and the hip. (This is the opposite of phase 3, where the main goal is the lengthening of the distance between foot and hip.)

  • Put the leg joints into a more effective configuration for phase 3 (and perhaps for phase 2).

drivers of propulsion

?? [ to be added ]

[ physics and biomechanics parameters that drive the amount of added propulsion work -- and the additional time it takes to perform that work. ]

 

muscle moves

??

for forward propulsion:

??

and perhaps initiation of

  • forward-pelvis-rotation - [ see more ]

for transmission:

  • hip-abduction -- valuable for "isometric" static transmission of sideways kinetic energy from previous leg-push, even if not yet used for active propulsion work:

details + hints

static transmission + support

  • Transmit the side-weight-shift kinetic energy from the sideways component of the leg-push and upper-body moves of previous phases (including phases associated with the other leg).

  • Maximum transmission -- no absorption -- no collapse.

No absorption by allowing the pushing hip to go outward. The hip abductor muscles must "stabilize" the hip -- fight the momentum of the pelvis and butt toward the next pushing side. (Though the torso and shoulders can continue moving sideways a little longer -- their timing is different, because they do not have a transmission stability role.)

  • Support the Phase 3 push of the other foot by at least trying to hold position relative to it, even if there is no push-motion visible yet from this new 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.

early non-extension push

  • Push out toward the side with the transverse hip-abduction move.

These hip-abduction muscles are not large, but every little bit helps -- to take load off the obvious big leg muscles.

Even if they do not have the strength to actively push the hips thru any visible range of motion, at least the hip abductors should be developed enough to "isometrically" stabilize the side-weight-shift of the hips at the right time, and fight to prevent the hips - pelvis - butt from moving any further toward the next pushing side. They can try to hold the hip stable for transmitting the side-weight-shift force.

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 holding this hip stable can provide a "fixed point" for the previous leg to push against -- which adds to the effective force transmitted to the snow.

The endurance and strength of the hip-abduction muscles can be developed with specific training exercises. Typically human muscles can apply more force when holding stable ("isometric") than when making an active push motion. And more force when actively pushing slowly than when pushing faster. So even a small muscle thought to be weak can play a key role in the chain of transmission of big force and power, even if it shows no discernable motion.

  • Ankle-pronation move -- bending the ankle inward and the foot outward some in phase 1 can also add to propulsion.

"pronating" = bending the ankle joint sideways toward the inside of the knee-heel line.

But pronating adds work to propulsion only if it is performed by active pulling by the ankle-pronator muscles -- not just allowing the ankle joint to collapse downward.

[ inline: In "double push" technique, supinating the ankle can add propulsion to the first (inward) push of the stroke. ]

(If there is a leg-passive glide phase to focus on pole-push, the start of this move might be delayed to Phase 1b.)

Bending to too large an angle of pronation results in more negative work than positive -- because pronation also shortens the overall leg-length. So need to stay within an angle small enough so that the side-and-back push component is larger and the impact of the component from shortening is smaller. Starting the pronation move at an earlier Phase when the overall leg is more vertical helps keep the negative component from shortening smaller. Then in later phases supinate the ankle to get the benefit of full leg extension.

Though often criticized by instructors, pronation is not all bad. It is bad as a position in Phase 0 (over-edging) and in Phase 3 (lazy collapse) -- which is what instructors see reducing leg extension and power in many skaters. But an ankle-pronation move is beneficial for power in Phase 1 and perhaps Phase 2, provided the skater uses actual muscle-power to do it (instead of lazy collapse) and remembers to re-straighten using the ankle-supinator muscle for full extension in Phase 3.

(Setting down with the ankle in a somewhat supinated position would enable a larger positive-propulsion range-of-motion for the ankle-pronator muscles -- but for ski-skating on snow that's not usually going to fit with the need to push through the inside edge. So usually the best that ski-skaters can work on is trying minimize the pronation at set-down.)

[ inline: In normal-push stroking, there can be benefit to setting down with the ankle in a supinated position -- if you have very well-trained ankle-pronator muscles to exploit it. With "double push" technique, could set down with ankle vertically straight in line or pronated slightly, then the ankle-supinator muscles can help add propulsive work to the first (inward) push, so then the ankle joint is already in a supinated position at the start of the second (outward) push, and the ankle-pronator muscles have more range-of-motion available to add propulsive work to the outward push. ]

Note: This is remarkable, that both the original move (ankle-pronation in Phase 1) and its reversal (ankle-supination in Phase 3) can add positive propulsive work to the same overall leg-push on the same side. The explanation is that each is timed correctly with the vertical-angle position of the overall pushing leg. At set-down the leg is roughly vertical, so shortening in the line of the leg has only a small component of negative impact on forward-push or side-push, mostly just reduces the compression of snow underneath the ski base -- while the sideways component of the ankle-pronation move has full impact on side-push across the ground surface. At later phases of the leg-push the foot has moved out toward the side and back, so the overall leg is aimed out the side and back, so lengthening of the leg by the ankle-supination move then has a major component of impact on side-push and forward-push -- while the sideways component of that move is aimed only for a small negative impact, much of it just helps drive the edge of the ski more down into the snow.

  • 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-extensor muscles to operate in a less favorable segment of their range-of-motion in the next leg-push. Instead the forward-pelvis-rotation move advances the hip and foot together.

 - - might help remind the hip abductor muscles to do their pushing.

If there is a leg-passive glide phase to focus on pole-push, the start of this move might be delayed to Phase 1b.

exercises

to sensitize to feeling how to push with the three non-extension side-push moves:

  • two-leg parallel non-extension forward slalom:  Feet shoulder-width apart, big knee bend so hips are low like at set-down. Keep feet parallel at times, push first with both legs aimed diagonanally toward the left side (left foot on inside edge, right foot on outside edge), then push with both legs aimed diagonanally toward the right side (left foot on outside edge, right foot on inside edge), and repeat several times. Keep feet parallel to each other at all times, same width apart at all times (no "sculling" of one toward or away from the other).

Focus on using only transverse-hip-abduction, inward-hip-leg-rotation, and ankle-pronation to push outward with the foot on inside edge. At the same time "mirror" those moves with the other leg on its outside edge so it stays parallel -- so it will be doing the opposites to the three inside-edge moves: transverse-hip-adduction, outward-hip-leg-rotation, and ankle-supination. The main role of the outside-edge foot is to make the balance easy, but training these three outside-edge moves will also help propulsion if ever use double-push technique.

No vertical motion of the hips. No "carving" or slicing forward with the knee-extension muscles. Try to keep upper body quiet and facing forward, no arm-swing.

For each of the three moves: (a) try to feel range-of-motion, play with maximum starting position, play with maximum finishing position; (b) feel the force and push transmitted into and through the foot by the move, more than "going through the motion", try to actively push at the start, and actively push through the finish; (c) feel the timing of which segments of the leg-stroke are most effective for pushing, and which are better left as a quiet transition to or from the other side; (d) feel the "mirroring", notice how the maximum finish toward one side puts the knee and ankle into position already for maximum start toward the other side.

  • test of propulsion: climb up a gentle hill using only two-leg parallel forward slalom.

  • single-leg non-extension slalom (with toe-ride-balancer on inlines). Same moves as two-leg parallel non-extension slalom, but with only one leg doing all the pushes toward both sides. With inline skates, the other leg trails behind only for balance, with only its toe-wheel down. Hip and upper body stays quiet, no hip-extension permitted, and try to avoid knee-extension forward-slice.

At first, can get moving forward using normal skating, and just "go through the motions" of this exercise without worrying about pushing -- just to get comfortable with the balance of changing the aim and tilt directions while gliding on a single leg. Once comfortable with the balance, again get moving forward using normal skating, then use the moves of this exercise to try to maintain forward speed, or at least see how far can keep going before come to a stop or lose balance.

The next level of difficulty is to take away the support of the trailing toe-wheel skate.

This exercise is also excellent training for extracting maximum propulsion from the in-push phase ip1 of double-push technique.

Final exam: single-leg non-extension slalom up a gentle hill.

ski-skating alternatives

?? intro

alternate sequence

??

Phase Ski 1a = land w isometric hip-abduction and isometric inward-hip-leg-rotation, to transmit side force from previous phase.

Phase Ski 1b = (optional) passive glide

Phase Ski 1c = inward-knee-roll and initiate ankle-pronation

Phase Ski 1d = ankle-flexion -- not in phase 2 because it's a contractive move.

includes

  • ankle-pronation move.

  • forward-pelvis-rotation move.

  • lateral-hip-abduction move. 

 

drivers of propulsion

??

muscle moves

??

see below under knee-drive move.

passive glide option

??

Sometimes it's desirable to have a phase with virtually no leg-push work. If so, this is a good place in the sequence for it.

Reasons for a leg-passive glide phase:

  • It makes a good time to focus on a big double-pole push -- notably in V2 and Open Field Skate / V2A on skis.

  • Sometimes it's just fun to enjoy passive glide -- notably in Open Field Skate on skis.

details + hints

  • [ ski: ] This is the time to apply the old advice to "glide on a flat ski".

Edge the ski a little during ski phase 1(a), then fully flatten it for this leg-passive-glide phase, then back on some edge for ski phase 1(c) or Phase 2 and beyond.

  • Warning: Sometimes the elite ski racers look like they are doing a leg-passive glide phase in their V1 skate up a hill, but really it's Phase 1a: Transmission and Hip-Abductor push.

It's very hard to tell the difference between Phase 1a and leg-passive glide just from analyzing a video -- instead for reliable detection would likely need to put force sensors into the skate or the ski binding.

knee-drive move

??

This move is used mainly by ski-skaters, not expert ice or inline speedskaters.  Question: Why the difference?

?? perhaps this move is better done in set-down phase 0, so the leg is already in position for effective knee-extension before the leg-push starts.

muscle moves

for forward propulsion:

prerequisite configuration:

  • inward-knee-roll = inward-hip-leg-rotation combined with tranverse-hip-adduction (or at least combined with lack of hip-abduction support).

details + hints

  • Ankle flexes forward deeply -- which moves the hip joint forward so it is in front of the ankle joint.

?? but maybe this is better done on set-down phase 0

The knee joint might extend slightly, but the key thing is just to not let it collapse and absorb at all -- for full transmission of other forces.

And delay most of the main leg-extension push thru the knee joint (by the quadriceps muscles) and hip joint (by the gluteus maximus muscles) until after the knee and ankle joints are in best biomechanical geometry relative to the hip joint.

This an ankle-flexing move, not just a flexed-ankle position. Having the ankle flexed foreward is generally a good position for skating. But the point now is to flex the ankle foreward even more -- more flex than could be sustained generally through most of the leg-push. Maximum ankle-flex at the moment of the big payoff -- just in time for the main leg-push.

This move requires using muscle power -- the shin muscle (on the front of the lower leg). Lots of skaters do not have much endurance and strength in their shin muscles.

?? but maybe this move can take place in set-down phase 0 -- why can't you maintain the position easily, since there's body-weight over the knee.

[ ski + klap-skate: Keep the heel down. It's easier to drive the knee down if the heel is allowed to come up off the ski, but it's too early for that in this phase. The heel needs to stay down in the ski now -- to be in position for maximum transmission of the main leg-extension force in Phase 2. ]

For some reason me and lots of people find that thinking directly about ankle flex doesn't engage the specific muscles enough. I find it's valuable to think of it as a "knee-drive" move: driving the knee down and forward toward the ground -- see more below.

If the ankle is flexed straight in the direction of the aim-angle of the skate or ski, then the shin muscle is only helping achieve a helpful biomechanical alignment for Phase 2. But there's also a way to use the shin muscle to apply forward-propulsion work -- see below.

  • ?? Inward-knee-roll move -- Rotate or "roll" the knee inward using muscles on the side of the pelvis.

This "inward knee roll" move pushes the foot a little ways out and back, and the upper body a little in 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.

(If there is a leg-passive glide phase to focus on pole-push, the start of this move might be delayed to Phase 1b.)

The trap is that the "natural" way to do this move is to allow the pushing hip to move outward at same time the knee moves inward -- in which case the side-force benefit of the inward knee move is mostly lost. The inward-knee-rotator muscles must work together simultaneous with support of the hip-abductor muscles.

Video checkpoint: In front view, the pushing hip should be vertically above the knee at set-down. The hip should remain vertically above the knee during Phase 1. In elite-racer skating, the shoulder normally moves outside the knee and hip during Phase 1, but the hip does not move outside the knee.

This move also configures the leg for propulsive moves in later Phases by other muscles:

(a) if the knee is inside the hip+heel+toe plane, then the forward-ankle-flex / knee-drive-heel-drive move in Phase 1b has propulsive benefit. If the knee were in the plane of hip+heel+toe, then flexing the ankle would exert force only in the line of the ski or skate, which cannot have any significant propulsion benefit (unless the glide wax on the ski base is not working or the bearings on the skate wheels are bad).

(b) The leg is bent sideways in the middle and thus slightly shortened by rolling the knee inward. So in a later phase the knee can be rolled outward and the leg straightened and thus lengthened. This is propulsive work added by the knee-rotator muscles on the opposite side, operating to reverse the earlier Phase 1 move by this side's knee-rotator muscles.

?? This move could instead be performed in set-down Phase 0.

Drive the knee down and forward. Drive the heel down and back.

This is not a "forward step".

It is rather a "scissoring" of the legs. The recovering foot goes forward, but the pushing foot goes backward. The "going back" part is the heel-drive move -- driving the heel back, so the ankle joint moves behind.

[ ski + klap-skate: ] Driving the heel down and back also helps to make sure the heel stays down on the ski for the start of Phase 2 -- to be in position for maximum transmission of the main leg-extension force.

For me it helps to try out both mental images: Driving the knee of the pushing leg down and forward; and Driving the heel of the pushing leg down and back.

  • There's usually also some bending of the knee.

This prepares for a larger range-of-motion by the knee-extensor muscles in full extension push of Phase 3.

Some coaches think that this knee-drive move is a knee-flex move, and neglect the ankle-flex aspect. I think the knee-flex interpretation is a confusion of a move with a position. For the ice and inline speedskating, a position with strong knee-bend is important for (a) aerodynamics at higher speeds; (b) the knee-extensor muscles can push effectively through a larger range-of-motion in the lower-force, lower-gliding-friction context of ice or wheels on flat or gentle courses; (c) how much and how long a strong knee-bend position can be sustained is a key bottleneck in ice and inline race performance; (d) for non-klap ice and inline equipment, it is not so obvious how the ankle-flex move also prepares for later additional propulsion.

My response to the knee-flex interpretation of the knee-drive move is: (a) ankle-flex delivers additional propulsive work immediately in Phase 1b, provided that the inward-knee-roll move was started in Phase 1a; (b) the ankle-flex move shifts the hip forward ahead of the ankle, so that the later knee-extension move in Phase 3 has more of an outward-sideways component and less of a slicing-forward component, and is thus more effective for propulsion; (c) for klap-skate equipment, including ski-skating, the ankle-flex now increases the range-of-motion of the toe-push extension in Phase 3b, which adds propulsion work.

?? Note that (b) is really key, and for that purpose the ankle-flex move could be performed in set-down phase 0.

Note: I find it remarkable that this knee-flexion move means that there is a definite shortening of the effective leg extension length during part of the leg-push. Which contradicts the obvious idea that the leg-push should be a continuous lengthening of extension. This shortening can work because it comes at an early phase when the leg is nearly vertical, so the backward and sideways push components of its leg-pus vector are small, to the loss of propulsion is small. The main effect of the shortening in this phase is a "lightening" of the vertical weighing down, which does not significantly affect propulsive work (unless it makes the foot lose grip to push outward across the ground). Later in Phase 3 when the corresponding lengthening occurs, the skate or ski is angled vertically relative to the ground, so the proportion of the backward and sideways components of the leg-push vector are larger. So there is a substantial net gain in propulsion work.

?? but this shortening could be avoided if the knee-flexion where performed during set down Phase 0.

  • How much angle of forward flex of the ankle?  More.

The more angle, the better positioned are the hip and knee joints for the Phase 3 extension push -- and the more propulsion work arleady in this phase. It's pretty amazing how sharply the elite ski-skate racers angle their ankles forward in Phase 1 of their leg-push.

If the knee is angled inward relative to the aim-angle of the pushing skate or ski -- by using the inward-knee-roll move in Phase 1a -- then the knee-drive move will be aimed partly forward in the direction of the skater's overall motion.

So the action of the shin muscle in flexing the ankle will also be doing some direct forward-propulsion work, by moving the skater's hips and upper body forward against air resistance (or against gravity, if going uphill). Perhaps it also helps the leg muscles push more out toward the side.

? A possible downside is that moving the knee inward takes it slightly out of the straight line of force transmission. But perhaps enabling the direct propulsion work by the shin muscle is worth it. The biomechanics and physics of this get rather complicated. Actually there are several other cases where the joint-configuration geometry used by winning elite athletes does not follow the obvious planar alignment that would be guessed from simplistic biomechanical analysis. Anyway this concern can be addressed by . . .

Don't forget later in Phase 3 to reverse roll the knee out into straight alignment in the toe-heel-hip plane.

Key point: Even if allow the knee to angle inward slightly, do not fall into the tempting corollary of allowing the hip to swing outward. Because that's a larger deviation from the straight-line for side-force transmission, a major absorption -- and without any compensating benefit.

more . . .

see also

[go/motion/z_text_line.htm][go/motion/z_text_line.htm]

concept words: skating skate skates skater skaters push glide inline inlines ski skiing snow roberts

skating: skate skates skater skaters push glide

inline inlines ice speed speedskate speedskating speedskater speedskaters roller

technique: techniques technical theory theories theoretical physics physical biomechanics biomechanical mechanics mechanical model models concept concepts idea ideas