what's here

• overview | priorities | phases

• extension push

• out-sweep push

• pelvis + upper body

• "gear" selection

• more . . . aerodynamics | gliding resistance | poling

Unlike some other human propulsion motions, skating has very complicated 3-dimensional physics, and most of its individual moves are un-natural.

Seated bicycling pedaling is comparatively simple, and walking and running are pretty natural.

So there's no "three simple secrets" which once mastered will make the rest of the action easy. Each move has individual aspects which can either enhance power or get in the way.

High Priority

Everybody has their own strengths and weaknesses and their own history of habits. But here's some likely big wins for lots of learning skaters:

• Consciously work on the Out-Sweep move -- and delay the start of the Extension move.

• Consciously work on the Knee-extension move in phase 3 -- and use the ankle+knee flexion "knee drive / heel-drive" move in phases 1+2 to prepare for it. (Practice the curved "C-stroke" of foot relative to hip.)

but once the power of the Knee-extension move is practiced and felt, there's no point in being religious about it -- allow the unconscious neuro-muscular control module decide the best proportion and timing of Knee-extension "carving forward" versus Hip-extension to push more toward the back.

• Get the pushing-side hip lower for the second half of the leg-push (especially for higher speed situations).

but for higher force / lower speed situations, a generally higher hip is often better, because it allows a lower "gear ratio" for the Hip-extension, Knee-extension, and Medial hip-knee rotation moves.

• Stable Hip-abduction muscles to transmit sideways Out-Sweep force + power to upper body mass at the moment of set-down of the foot.

• Do not allow upper body mass to start moving sideways toward the direction of the current leg push.

but it's OK -- often good -- if it's already moving that way at the start of the leg-push.

for "surviving" climbing steep hills

• Use lagging "backward" pelvis/hip rotation to ease power demand for climbing steep hills (turn the "belly button" toward the next pushing foot).

• Keep the hips generally higher, to give the Hip-extension and Knee-extension muscles, also the Medial hip-knee rotation (Out-Sweep) muscles in a configuration of lower "gear ratio" -- better to deliver higher forces.

phases

the "normal" skating leg-push has three main phases: (1) Out-sweep, (2) Between, (3) Extension.

The following descriptions of phases are for pushing with No poling. When poles are used to help push, there are some important changes in the leg-push sequence made to better exploit the pole-push.

phase 1: Out-sweep underneath

This is while the foot is roughly underneath it's hip, with the "leaning" angle of the hip-ground-contact line in the range of roughly -15 to +15 degrees from vertical. This is the range where Out-Sweep moves can make their best contribution to forward propulsive work, because the tangent vector to their rotation has substantial component aligned with pushing direction of the leg. The Extension moves can make almost no contribution in this range. So the key actions are:

• quick strong transmission of sideways motion from previous leg-push on other side.

"quick" so the muscles can move on to other propulsive roles, not wasting precious stroke-cycle time.

• strong execution of Out-sweep moves

for higher speed situations with a lower hip position, the hip-abduction muscles are in a better configuration to deliver a longer range-of-motion at higher speed in the Out-sweep push. for lower speed / higher force situations with a higher hip position, the medial knee-hip rotation muscles are in a better configuration to deliver higher force intensify into the Out-sweep push.

• prepare for future Extension moves (by executing the ankle-flexion / knee-drive / heel-drive move)

• not start any Extension moves.

• finish "leading" pelvis/hip rotation and upper body side-swing moves which had been started in previous leg-push by the other leg.

• start moving the foot backward toward underneath its hip.

Typically this makes the hip rise a little. Once the other leg has finished its Extension push and lifted up, there's no propulsive benefit to having the hip low in late phase 1 and early phase 2. The rising of the hip is good for giving taking some of the isometric strain off the knee-extension muscles and knee joint. They don't have to exert so much force to support the weight of the upper body if the hip is higher; and moving them a little could help stimulate more circulation to remove waste products and bring in more fuel + oxygen. Just have to move the hip down low again later to be ready for phase 3.

To make it easier to raise the hip with less force on the knee-extension muscles, many elite racers simultaneously duck their shoulders down. The hips go up and the shoulders go down, so overall there is little actual lifting of the total weight of the upper body.

[ Double-push ] One possible advantage of the "Double-push" technique is that it enables the knee-extension muscles to add a little direct propulsive-push work at the same time.

[ note the secret inward push trick under Phase 2 ]

phase 2: Between

While the "leaning" angle of the hip-ground-contact line is in the range of roughly +15 to +30 degrees from vertical, neither the Out-Sweep nor the Extension moves are in their best configuration to deliver forward propulsion work -- and the key role of Out-Sweep muscles in transmitting sideways energy from the previous leg-push is already complete. So a key objective is to get through this phase quickly. Key actions are:

• get the pushing-side hip low, so the big extension push in phase 3 will put a higher percentage of its force directly into propulsion, and the horizontal distance of its push will be a little longer. (see more details here + here2)

Typically the hip will have risen a little at the end of phase 1 just after the other leg finishes its Extension push and lifts up. There's no propulsive benefit to having the hip low in late phase 1 and early phase 2. This rising is good for giving taking some of the isometric strain off the knee-extension muscles and knee joint. They don't have to exert so much force to support the weight of the upper body if the hip is higher; and moving them a little could help stimulate more circulation to remove waste products and bring in more fuel + oxygen. But then have to move the hip down low again to be ready for phase 3.

Two key components to this:

(1) Prepare to set down the other non-pushing foot more forward relative to its own hip, with less forward ankle flex (less dorsi-flexion), so it's easier to keep the non-pushing hip lower; and

(2) Move the pushing-side hip down lower than the other hip -- or at least not higher than the non-pushing hip. Likely part of this is to do a knee-flexion move -- increase the bend of the knee during this "Between" phase.

• bring the foot backward, so the ankle moves to roughly underneath its hip.

The reason is simple: You cannot get much work from the extension moves of the knee and ankle joints in phase 3, if you do not first un-extend them in phase 2. Un-extending means flexion.

Some people find it helpful to use a mental image of driving the knee forward and downward. Other people find if helpful to think of driving the heel backward.

Two key components in the biomechanics: (1) ankle-flexion, and (2) knee-flexion. In addition to moving the foot backward, knee-flexion is imporant also to keep the hip from rising.

• aim the foot more outward, so it can "glide" more quickly into the "leaning" angle range for phase 3.

There is a frictional cost to pivoting the foot, so how much to change its aim depends on what kind of equipment being used: The cost is small for inline skates and rockered-blade ice skates, so the pivot can be large. The frictional cost is more for long-blade ice speedskates, so the pivot is smaller. The cost is very large for normal-length skating skis, so there is no noticeable pivot at all.

[ Double-push ] An advantage of Double-push stroking is that it makes it easier to get thru this "Between" phase quicker.

Secret inward push trick: Another way to get through this phase more quickly is to set down the foot aimed straight in the direction of overall motion, and in Phase 1 push toward the inside, to generate momentum in the upper body toward the outside. Then use that momentum to more quickly "glide" out thru the "Between" zone. Sort of like a "secret" double-push, where there's an inward pushing, but no immediate direct forward propulsion work from it, and no visible inward arc of the foot. (see Chad Hedrick on ice in the later laps of the 2006 Olympics 10000-meter speedskating race)

• start upper-body side-swing moves

unless the turnover frequency of total stroke cycle is fairly slow, in which case hold them back until phase 3 and then execute them more explosively.

• perhaps continue some Out-sweep moves from Phase 1 (perhaps hip-abduction?)

especially if the "secret" inward-push trick was used in Phase 1.

• perhaps start some Extension moves ahead of Phase 3 (but not ankle-extension)

phase 3: Extension

The Extension push moves can have a substantial component in the direction of the pushing direction of the leg only if the "leaning" angle of the hip-ground-contract line is more than +30 degrees from vertical -- so this is where the must make their main contribution to forward propulsive work. The problem is that at this angle the hips and upper body are falling down quickly -- so there's not much time for it. This is also a good time for starting side-to-side moves higher off the ground. The Out-Sweep moves can make no contribution in this range. So the key actions are:

• strong quick "explosive" execution of Extension moves

• keep the pushing hip low -- try to move it lower.

• possibly set down the other foot before the current Extension push finishes -- to support the current push for a longer time in a lower hip position.

• start "leading" pelvis/hip rotation and upper body side-swing moves (if not already started in phase 2).

Extension push

The majority of pushing power for skating comes from pushing the foot directly away from its hip. The trickiness of skating is that the direction of push is never straight, and different from every other human propulsion motion -- a "diagonal" combination of three directions: downward, backward, and sideways -- and in most skating situations the pre-dominant direction for adding forward-motion power is sideways.

A key problem with this is that the skater has to be almost falling over sideways in order to aim the extension push mostly sideways.

concepts:

• Tricky conceptual point: The extension push normally cannot start at set-down. It must wait until the foot has moved a ways toward the side, a ways out from underneath its hip. This means that . . .

• The time and distance between set-down and getting out from underneath (Phase 1) can be used to prepare for the extension push. The way to get more out of extension is to first compress -- so that's normally a good thing to do just after set-down, which results in . . .

• Path of the foot relative to the hip might not be straight: Phase 1 of the push (just after set-down): the foot moves backward (compression from the ankle-flexion "forward knee drive" move) as it moves out toward the side. Phase 2 it moves roughly straight toward the side. Phase 3 it might move slightly forward (to emphasize Knee-extension) or somewhat backward (to emphasize Hip-extension).

There is no need to move the foot or aim its push exactly perpendicular to the aiming or gliding direction of the foot. The "magical" physics of the skate-to-ground contact will accept any motion or push applied vaguely perpendicular to the aiming or gliding direction, and convert it into forward propulsion work. So to some extent you can take some freedom in moving and pushing in the direction that's strongest for the different muscles, and let the "magic" of the skate take care of using it the best way.

hip-extension move

This is the biggest move in skating which is shared with the natural motions of walking and running.

common problems:

• trying to push too much straight backwards, to make it like walking and running.

symptom:  looks like trying to walk on skates, from a side view.

why it's a problem:  The skate cannot transmit force directly backward, so it tends to "slip".  More subtle:  Making the stroke too much like stepping, not enough gliding, limits the maximum speed -- because when the speed gets higher, the "stepping" foot cannot match speed with the ground.  Pushing out toward the side is the only way to get around this limiit of matching speed with the ground, to achieve speeds much higher than running.

• starting it too early, while leg is still too vertical and the foot too close underneath its hip.

symptom:  lifting the foot higher off the ground while recovering it inward thru the air. This is often a sign that the skater is trying to get the hip-extension move started immediately at set-down -- or even before set-down -- by "stomping" the foot. The foot is (unconsciously) recovered high in order to stomp it down.

why it's a problem: If extension push starts too early the push is aimed mostly downward, not out toward the side. The downward component only raises the mass of the upper body, instead of contributing directly to propulsive force. Raising the upper body can help propulsion indirectly, but it's slower, so the rate of power isn't as high.

• pushing-side hip doesn't get low enough (especially for higher-speed situations). This is very key for effectively delivering the push directly into effective propulsive work. Difficult to feel it: Need to check it with an (experienced) external observer or video.

• dropping the non-pushing hip low. This feels like it makes it easier for the hip-extension muscles to push out toward the side (good idea). But it prevents the pushing-side hip from getting low enough, and that's more important.

• push is too slow, not explosive enough.

• taking the "pushing straight to the side" concept too literally. It's a helpful mental image for practice, but to use the hip-extension muscles effectively in actual performance, the push must move the foot partly backwards -- it's just how the hip-extension move works. Trying to avoid that backward component reduces speed.

physics + biomechanics: The propulsive component of force in pure skating is the component which is perpendicular to the aiming-gliding direction of the foot. But there's no need for the motion direction of the foot to copy the force direction -- as long as the motion direction has some component in the direction of propulsive force. Nor is there much advantage in avoiding force components which are not in the propulsive direction. The point is to get a larger propulsive component -- if the muscle more which produces a larger propulsive component also includes a significant non-propulsive component, that's usually not a reason to avoid it.

Both the hip-extension and the knee-extension moves can have a component in the propulsive force direction, but they will also have other components: The knee-extension move tends to "slice" the foot forward, while the hip-extension move tends to push the foot backward. But the hip-extension move in skating is much larger, so it wins -- so the foot moves backward (as well as sideways). This is obviously visible in videos with good side views of eliter racers.

concepts + moves:

• practice pushing straight out toward the side -- and discover the magic of skating: that the skate can transform a sideways move into forward motion.

but you do that literally only in practice, to develop your feel for this non-intuitive motion -- so your unconscious neuro-muscular control module develops a strong awareness and competence at controlling the move.

For maximum sustainable speed in actual performance, the most effective push is diagonal -- partly sideways and partly backwards. The optimal blend of sideways and backwards is something you can play with. Then in actual performance it's best to leave the proportion and timing of it's use to the unconscious neuro-muscular control module -- not try to control it by some simplistic rule in your rational conscious mind.

• when recovering the leg inward thru the air, bring it in underneath further than where you will set it down and get it close to the ground in that position -- then make it so the last move before set-down is mostly outward -- like you're starting the Out-sweep move already in the air.

This adds force to the previous leg-push, and tends to make the transmission of side-motion into its own Out-sweep push quicker and more "rigid".

• try holding back on the main Extension push until you've almost fallen over sideways, then make it explosively.

This timing applies a larger percentage of the Extension push while the leg-lean angle is transmitting a larger percentage of its work directly into forward propulsion. But the point here is to allow your unconscious neuro-muscular control module to get the feel of this non-intuitive timing as an available option -- (not to try to force it in actual performance as a simplistic rule by the rational conscious mind).

• it's OK to set down the next foot before the current extension push is finished. So you don't actually need to take a real risk of falling over sideways.

knee-extension move

The knee-extension muscles can be big and powerful. But this move has no use in the main push of walking or running, so people tend to overlook it for skating. Worse yet, it's opposite to one of the main pushing moves of walking: knee-flexion. The main moves of walking push the foot backward, but the knee-extension pushes it slightly forward -- so even when a skater does think about it, they tend to assume that it must be wrong and counter-productive for forward propulsion.

The human propulsive motion which shares the knee-extension move with skating is bicycle-pedaling. Most people can engage knee-extension muscles most strongly when they pedal standing up off the seat.

common problems:

• not doing it at all.

symptom:  foot trails back "naturally" in the final phase of push while still on the ground.

• not preparing for it by making the ankle-flexion "forward knee drive" move.

symptom: knee stays clearly behind the toe throughout the push.

why it's a problem: Range-of-Motion:  You cannot "slice" the foot forward with force against the ground any farther than you first draw it backward behind the knee.

• starting it too early.

symptom:  lifting the foot higher off the ground while recovering it inward thru the air, and starting the ankle-flexion "forward knee drive" move while the foot is still in the air (knee close to vertically over toe while foot is still in the air).  These are often a sign that the skater is trying to get the knee-extension move started immediately at set-down -- or even before set-down -- by "slicing" the foot forward. The foot is (unconsciously) recovered high and backward in order to slice it down foward.

why it's a problem: If the Extension push starts too early the push is aimed mostly downward, not out toward the side. The downward component only raises the mass of the upper body, instead of contributing directly to propulsive force. Raising the upper body can help propulsion indirectly, but it's slower, so the rate of power isn't as high.

concepts:

• practice not just pushing straight out toward the side -- but actually "slicing" or "carving" the foot forward as the push finishes -- and discover yet more radically the magic of skating.

• when recovering the leg inward thru the air, bring it in underneath further than where you will set it down and get it close to the ground in that position -- and slightly forward of the set-down position.  Then make it so the last move before set-down is mostly outward and somewhat backward -- like you're starting the out-sweep move and starting to drive the heel back already while it's still in the air. Image that the initial move of the skate immediately after set-down is outward and backward, not downward or forward.

• try holding back on this "slice" or "carve forward" move, then make it explosively at the finish of the main push.

ankle-extension move

problems:

• trying to push too much backwards, to try to make it like walking and running.

symptom:  looks like trying to walk on skates, from a side view.

• pushing too early and too much backwards.

symptom:  looks like trying to walk on skates, from a side view.

why it's a problem: (a) ankle-extension blocks the preparation and triggering of the more powerful knee-extension move; (b) The heel needs to be down against the ground thru most of the extension push -- to fully transmit the big forces from the big hip-extension and knee-extension muscles. If try to push the ball or toe of the foot, you will tend to unconsciously hold back on the instensity of the other muscles to fit into what the ankle-extension muscles can handle; also . . .

(c1) on rougher pavement, minimizing the time with pressure focused on the front wheel helps roll over bumps easier; (c2) on snow (especially in softer snow) keeping the pressure focused further back on the ski helps the tip of the ski "plow" less deeply into the snow; (c3) on a non-klap ice skate, pressure unevenly distributed toward the front of the blade increases friction and decreases control.

• not believing that ankle-extension can possibly add power to inline skating

• not believing that ankle-extension is ever appropriate for inline skating

concepts:

• Allow the unconscious neuro-muscular control module to determine the appropriate amount of "toe-push".  Most skaters should not think consciously about making an ankle-extension move -- any conscious attention should be on pushing thru the heel.

• inline skates: It is possible to add propulsive power by making an ankle-extension move with an inline skate: by pushing with only the front-wheel rolling on the ground. This is visible in single-frame-advance or slow-motion analysis of videos of world-champion inline speedskaters.

• timing: the ankle-extension move should be only a final "flick" as the foot lifts off the ground -- like the second half of Phase 3.

ankle-flexion move

"forward knee drive" or "backward heel drive" are other images for this move.

Not an extension move -- actually it's compression. But a critical preparation for extension which is not intuitive.

Benefits:

• increases range-of-motion for knee-extension move.

• increases range-of-motion for ankle-extension move.

• maintains forward balance if hip is lowered to increase range-of-motion further for hip-extension and knee-extension moves.

• can reduce air resistance by moving the chest and shoulders more down and forward (without increasing isometric strain on back-extension muscles)

feels like driving the knee down and forward toward the toe -- or like driving the heel back behind.

visual checkpoint: knee moves to vertically over the toe. This move is unusual so it should be easy to notice in side-view video -- or by an experienced observer without video.

Some skaters try to see it for themselves by checking if their knee comes between their eye and their toe. The problem with this is that it depends on head position and on how much back is bent to bring the shoulders and head forward -- so it might be unconsciously tempting to do something unusual or unhelpful with the back or the head in order to make the eye - knee - toe observation come out "right".

timing: this move is normally executed during Phase 2 or the later part of Phase 1 after the other leg has finished its main Extension push.

There might be special cases requiring very high force (e.g. steep hill or starting sprint) where Phase 1 must be shortened to virtual non-existence, so most the ankle-flexion move must instead by executed before set-down while the foot is recovering thru the air. But doing it earlier than necessary puts more isometric strain on the (typically smaller + weaker) ankle-flexion muscles, and tends to raise the hip of the other leg which is still finishing its push (which makes that previous push deliver less direct propulsive work).

training development: the ankle-flexion muscles aren't used strongly in most human tasks -- and normally not at this extreme "forward" segment of their range-of-motion. So they need to develop lots more strength and endurance and flexibility to handle the demands of a critical role in supporting the main skating push.

Many people feel soreness in their shin muscles (on the front of the lower leg) when they start working seriously on skating more strongly. Don't overdo it in the first sessions -- give them a few weeks of progressively increasing usage duration. Be nice to those little ankle-flexion muscles and they'll unleash new power from your big muscles.

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Out-Sweep push

The out-sweep push moves are not used by most other human propulsive motions, but they can make a substantial contribution to skating power.

[ In-Sweep push of Double-push stroking: mostly similar problems and concepts, but in the opposite direction and with opposite muscle moves: ankle supination, lateral hip rotation, and hip adduction. But the optimal proportions of timing and force and range-of-motion between the muscle moves might be different from Out-Sweep. ]

problems:

• Setting down with the leg in a configuration where very little out-sweep range-of-motion is possible: e.g. foot far outside from underneath its hip, or ankle already pronated.

[ In-Sweep push of Double-push stroking: Problem is setting down foot too far inside underneath it's hip. ]

• Inconsistent execution: Major positive out-sweep in one muscle move together with substantial negative out-sweep from another (typically positive medial hip-knee rotation together with negative hip abduction) -- instead of smaller positive out-sweep from both, or positive out-sweep in one and static transmission in the other.

• No awareness that the Out-Sweep move uses force + power from specific muscles -- rather thinking that it's only a kind of "falling" -- so no specific training is offered to those muscles.

[ In-Sweep push of Double-push stroking: Problem is thinking that it's about making an S-curve, instead of how to get additional force + power from different specific muscles. ]

• Terminology that refers to the phase just after set-down as the "Glide" phase, with the "Push" phase coming only after the foot is tilted onto inside edge and moved out from underneath its hip.

• some athletic skaters tend to over-estimate their side-to-side motion -- it feels like a lot, even though it is much smaller than elite racers.

Elite racers in videos tend to look so smooth that it's difficult to imagine how much larger their side-to-side motion is.

For some athletic skaters, adding more sideways motion can feel very "aggressive" and radical and not smooth -- thus not like the look they perceive in elite racer videos.

So they assume their current sideways motion must be about right, and they go looking for points of unstable transmission, or do training to add quickness.

ankle pronation move

problems:

• setting down with the ankle already pronated.

• believing that all ankle-pronation is bad.

• not training the ankle-pronation muscles for propulsive motion.

concepts:

• setting down with ankle not already pronated feels un-natural.

Need to visually check that the ankle is vertically above the ground-contact line under the foot. Do specific drills to practice this repeating lots.

Consider practicing setting down with ankle in a supinated position.

• stable transmission comes before active propulsive motion.

If do lots of skating with time for specific drills, sufficient strength can usually be attained for the ankle-pronation muscles to be able to hold stable to transmit force + power from other Out-Sweep moves.

If not time for enough specific drills, need to use a boot with a higher stiffer cuff over the ankle, so the boot can provide additional support to enable the ankle-pronation muscles to hold stable. A side-effect of such a boot is that ankle-pronation muscles will be less able to contribute active propulsive work.

• ankle-pronation move can actively contribute propulsive work.

Many videos of the fastest ice and inline speedskaters show them doing this, especially in non-high-force situations. With specific training of the muscles, lots of other skaters can do it too.

But in high-force situations, the ankle-pronation muscles are usually not strong enough to contribute much active work, and take more of a static transmission role. Due to the slower surface and hillier terrain of cross-country ski races, elite ski racers typically use little or no range-of-motion for ankle-pronation (instead more emphasis on active medial hip-knee rotation move), and skate boots for cross-country skiing typically have higher stiffer ankle cuffs.

• ankle-supination position at set-down can add range-of-motion to the active ankle-pronation move.

There's nothing in the physics that makes setting down with ankle straight and skate blade or wheels exactly vertical. (But in some snow conditions the transition from outside thru flat to the inside edge of the ski base does not work so well, and generally elite ski racers do not set down with supination.)

Ankle-supination position at set-down (blade on outside edge) is often seen by elite ice speedskaters on straightaways.

Tricky point: Even if the ankle at set-down is straight (neither supinated nor pronated), the skate blade or wheel-frame could still be tilted onto outside or inside edge. Because other Out-Sweep muscles might be tilting it (medial-hip-knee-rotation or hip-abduction).

medial hip-knee rotation move

Typically the largest active range-of-motion distance of the three Out-Sweep moves.

problems:

• setting down with partial medial-hip-knee-rotation already (knee pointing inward from the aiming of the foot)

[ In-Sweep push of Double-push stroking: Problem is setting down with knee pointed too far outward toward aiming of foot. ]

• believing that medial-hip-knee-rotation is bad -- that the "proper" way to skate is with the hip, knee, and ankle to always be in straight alignment.

• not transmitting the good work of medial-hip-knee-rotation move by keeping the hip-abduction muscles stable.

concepts:

• medial-hip-knee-rotation surely contributes positive propulsive work. The move is plainly visible in videos of elite speedskaters, and especially elite cross-country ski racers.

• setting down with knee pointed outward adds range-of-motion distance to this move. The old tip is to align the aim of the knee with the aim of the toe (at set-down).

• climbing a steep hill: combining a generally higher hip position with aiming knee out over toe enables medial-knee-hip-rotation muscles to operate at a lower "gear ratio" (shorter sideways push distance for the same rotation angle), so they can sustain higher force intensity.

Well-trained skaters can usually generate significant positive work from this move when climbing up a hill.

But the higher hip position tends to unfavorable to the hip-abduction move, so it's usually better to de-emphasize that in higher force situations, use if more just for stable transmission.

• development:  the medial hip-knee rotation muscles are very well trained on a slideboard.

With clever adjustments of the settings, it might be possible to train these muscles with the "rotary hip" weight machine in some gyms or fitness centers.

Seems like for most skaters stable transmission is usually not a problem with this move -- and if it were a problem it could be easily solved by position the knee somewhat more inward at set-down. So the training focus can be on active positive work from this move.

transverse hip abduction move

The hip-abduction move is too far from the foot to add much propulsive power to the Out-sweep push (for many skaters in many situations other than high speed / low force) -- the long "radius" means that the torque is too large (especially for high-force situations, e.g. climbing a steep hill) -- typically well outside the favorable segment of the torque/power curve for this muscle move.

In low force situations, e.g. ice skating on a straightaway, perhaps the hip-abduction move can also actively add significant power of its own, if it's been developed to be very strong.

Elite racers have different torque/power curves from the rest of us, so they might effectively use a positive hip abduction move in lots more situations than the rest of us.

Using a lower hip position at set-down tends to reduce the "gear ratio" of this move (enables a shorter sideways pushing distance for the same joint-rotation angle), which might make it more likely to be able to use this move to add some positive work in the second half of phase 1 or in phase 2.

The higher hip position typically used for higher force situations is unfavorable for the hip-abduction move, but more favorable for the medial hip-knee rotation move -- so in those situations its usually better to emphasize the action of the medial hip-knee rotation move, and use hip-abduction more just for stable transmission.

So the critical role of hip-abduction move is solid transmission of power (a) from sideways motion of upper body weight from the previous leg-push into the ground; and (b) between the lower out-sweep moves (ankle pronation + medial hip-knee rotation) and the mass of the skater's upper body.

problem:

• allowing the hip to move outward while the knee moves inward

symptom: hip is vertically above knee at set-down, but after Phase 1 the knee has moved inward relative to the foot, but the hip is still out toward vertically over the foot -- no longer vertically over the knee.

In a front-view video, after Phase 1, the knee-ankle line is normally tilted substantially toward the other leg (good), but the problem is if the hip-knee line is tilted noticeably away from the other leg -- so the ankle-knee-hip makes a substantial zig-zag. Variation: Hip lags outside knee just after set-down, but quickly "catches up" to the knee before the end of Phase 1.

Self-check: No need to wait for a video session: The skater can simply look down at the pushing and see what's happening. During phase 1, the foot should move obviously out toward the side, while the knee should be roughly underneath the eye. The problem is if the hip is somewhat out toward the side, instead of directly above the knee. With practice in visual self-checking, can improve the perception of what solid hip-knee transmission should feel like. Sometimes start the visual monitoring immediately on set-down to check for an initial failure of the hip to track the knee, then learn the neuro-muscular coordination to get the hip-knee transmission "solid" from the start.

The sign of good transmission is if after phase 1, the knee-ankle line is tilted substantially toward the other leg, and the hip-knee line is vertical -- so there's a noticeable bend in the ankle-knee-hip line, but not a zig-zag. The point is that the hip should "track with" the knee during phase 1: the knee moves down and in, and the hip moves down and in with it. (If the hip-knee line is tilted slightly toward the other leg after phase 1, that's even better -- but likely not worth trying to achieve in high-force situations).

why it's a problem: If the hip is opposite to the knee, then good work of pushing the foot out away to the side is being "absorbed" in the hip-knee relationship -- instead of fully transmitted into the mass of the upper body.

Even if the hip soon "catches up" with the knee before the end of Phase 1, the initial move just after set-down is the most effective propulsive configuration for the Out-sweep push, so failing to transmit fully at that short time is when it most hinders transmission of effective power.

concepts:

• the hip must keep moving away from the foot at least as far as the knee, in order to achieve full transmission of propulsive side-push force.

Especially at the moment of set-down it's important to initiate strong force in the hip-abduction muscles to withstand the initial (appropriately) strong push by the ankle-pronation and medial-hip-rotation muscles.

• obvious "trick" to keep the hip-knee relationship from moving the wrong way just after set-down is to start if moving the right way before set-down.

In the recovery of the leg, bring the knee further inward than it will be at set-down. Then just before set-down start moving the knee outward relative to its hip. Then when the foot "collides" sideways with the ground at set-down, the knee's motion will be slowed and changed from outward to stopped (which is good enough) -- instead of from stopped to inward (which is not so good).

• visual self-check -- by looking down at the hip and knee -- is helpful for learning the feel and the "un-natural" neuro-muscular coordination.

development of muscles:

These hip-abduction muscles are not used so intensely in other human activities -- except racket sports (e.g. tennis). Other than lots of skating with set-down underneath the pushing hip -- or even inside the two hips, here's some other ways to train these muscles:

• slide-board -- used much by ice speedskaters -- note how many of them develop noticeable muscle thickness on the side of their legs.

• weight machine for seated hip abduction is found in many strength-training gyms and health clubs. The key use of these muscles in skating is transmission: comparatively high forces at low speed (or zero speed: isometric). So training with a weight machine is more likely to be helpful for improving speed for this than for most other skating motions.

• keep in mind that for the hip-abduction muscles, for most skaters in most situations it's more important just to train them to be able to hold stable (against an inward push) than it is for them to push positively outward. So if there are exercises that focus more on stability, those might be the ones to prefer.

Pelvis-Hip rotation

The pelvis/hip rotation move is partly shared with walking and running -- quad-skating and cross-country ski Classic striding -- but it works for a slightly different reason in skating.

Pelvis/hip rotation is also a critical move for providing a "low gear" mode to handle a very steep hill without "burning out" the muscles for the rest of the day -- see gear selection. For that mode, the rotation goes in the lagging "backward" direction.

problems:

• believing that all pelvis-hip rotation is bad: either wasteful or counter-productive.

• believing that pelvis-hip rotation always ought to be used, and always in the leading ("forward") direction.

• believing that the torso and shoulders must (or ought to) follow the same rotational direction and magnitude as pelvis/hip rotation.

Perhaps strong skaters might think that leading pelvis/hip rotation must prevent effective torso side-swing. (Not a problem for most of us merely "athletic" skaters when climbing up a long steep hill, since lagging pelvis rotation aligns nicely with effective shoulder swing.)

• starting and finishing the forward move too early, so that it is synchronized with the start and finish of the leg-push.

concepts:

• Leading ("forward") pelvis/hip rotation adds propulsive work to the leg-push in the same simple way as several other moves, by accelerating mass away from the direction of the current push (reactive force, Newton's Third Law) -- and by decelerating mass already moving toward the current leg-push (reactive force, Newton's Third Law).

This implies that the positive effective propulsive work is largest at the start of the move, when the non-pushing hip is further back and closer to the gliding line of the pushing foot -- because there the "tangent vector" of its rotation path is aimed more perpendicular to the aim of the foot.

• Tricky timing:

What's tricky is that the path of the non-pushing hip sweeps such a large rotational angle, that the "tangent vector" soon aims more parallel to the aim of the pushing foot, which which reduces the component of its velocity directed away from the leg-push direction, which implies that the propulsive force soon goes negative (by Newton's Third Law). Bad thing: therefore it's important to time the leading rotation move so that this transition from positive to negative work comes around the time body weight is being transferred from one foot to the other.

So the timing of the leading pelvis/hip rotation move should tend to more synchonize with the timing of the torso-shouder side-swing move (and less with the start and finish of the main leg-push). (Likely most skaters will work out this timing more accurately by "feel" with their unconscious neuro-muscular control module, than by direct attention by the conscious mind.)

• Learn to "counter-rotate" the pelvis versus the shoulders. Often the correct direction for the pelvis/hip rotation move to contribute propulsive power is opposite to the correct direction for the torso-shoulder swing move. (Though the best timing is often similar).

• Use pelvis/hip rotation in two ways:  leading "forward" to add power to high-speed skating -- or lagging "backward" pelvis/hip rotation to ease power demand for climbing steep hills (turn the "belly button" toward the next pushing foot) (see "Gear" selection).

• Timing is very different for the lagging (or "backward") pelvis/hip rotation move sometimes used at very slow speeds: synchronize with main leg-push to avoid reducing the delivery of propulsive power -- see option (d) under "Gear" selection.

Upper body

Walking and running and seated bicycle pedaling -- also quad-skating and cross-country ski Classic striding -- have very little room for much positive contribution of moves above the hips to contribute to leg-push force. But because skating is truly 3-Dimensional, it is straightforward to use sideways upper body motions to contribute to propulsive forward-motion work.

problems:

• belief that upper body motion is mostly a waste of energy.

• focus on motion other than side-to-side: typical alternatives are rotation about vertical axis or forward-backward. Not recognizing that the component of motion other than side-to-side is typically self-cancelling over the whole stroke-cycle, so side-to-side is the simplest one to control for an overall net positive contribution to forward-motion power.

Sometimes people find it easier to "feel" the positive benefit from starting + accelerating some part of their body, but fail to "feel" the negative impact of decelerating + stopping that same part moving in the same direction. So they don't recognize that the overall impact on propulsive power is small or zero -- unless the move is carefully chosen and accurately timed.

Cross-country ski skating coaches sometimes get tangled in arguments over correct upper body rotation -- while what matters in the physics is the sideways "linear" component of the move.

• focus on the distance of the motion instead of the quickness (and frequency). Which often leads to focus on upper body moves reducing turnover frequency.

Distance is the easiest thing for coaches to observe, and the easiest thing to measure in video analysis -- so it's tempting to think that it must be the key factor of the move.

• timing is wrong: synchronizing with the leg-push normally makes the upper body work self-cancelling. Really bad timing can even subtract propulsive work from the leg-push -- and feel good while doing it.

Therefore if in doubt, do less with the upper body. Changing its moves with the rational conscious mind is more likely to make it worse than better for delivering propulsive power.

concepts:

• Torso-shoulder side-swing (when well-timed) adds propulsive work to the leg-push in the same simple way as several other moves, by accelerating mass away from the direction of the current push (reactive force, Newton's Third Law) -- and by decelerating mass already moving toward the current leg-push (reactive force, Newton's Third Law).

• The amount of propulsive Work added from a side-to-side move of the upper body is proportional to the maximum sideways speed at the moment of weight transfer from one foot to the other.

The total sideways distance moved is sort of related, but not the key thing. If the range-of-motion is cut short on each side, but the sideways acceleration is quicker, the Work from each move could be just as large, or larger.

At lower turnover frequencies [and perhaps for Double-push stroking], might get more propulsive Work by holding back on the start of the side-swing move, then making it quickly. Deliberately making it "jerky" instead of smooth might increase Work + Power.

• The amount of propulsive Power (in Watts) added from a side-to-side move of the upper body is proportional to the maximum sideways speed and the turnover frequency.

Trying consciously to increase the distance of side-swing range-of-motion tends to be counter-productive for turnover frequency, which often results in reducing Power.

"Gear" selection

Motor vehicles and bicycles make it convenient to manage key aspects of propulsion to meet different demands of different terrain and performance situations -- by selecting a "gear". The gear determines a ratio between the distance moved by an actuator (or key transmission point) and the distance of overall forward motion of the vehicle.

Once the gear is selected, the "driver" has a further choice of (a) how much force or torque to apply, or (b) what frequency of pushes (RPM) -- normally the performance limits on these two quantities are closely inter-related.  So there's a maximum force or torque that can be sustained at a given frequency of strokes per minute. And a maximum "cadence" or turnover frequency (RPM) that can be sustained at a given torque or force. The total Power (in Watts) is determined by the product of torque times RPM.

But skating is much more complicated, so it's not just a single numerical ratio that determines the relationship of force / torque versus turnover frequency RPM. There's other kinds of factors:

• range-of-motion distance per stroke of the actuator or key transmission point.

Often in skating it's simple to think of the transmission point as roughly the ball of the foot. And simple to think of the pushing distance as measured from the hip joint -- or perhaps more helpful to measure from the opposite hip joint -- or perhaps more theoretically accurate to measure from the "virtual" Center of Mass of the skater's body.

• distance "stepping" through the air versus distance "gliding" on the ground.

• passive gliding time in each stroke, before starting the active push.

• varying the geometry of angles and positions between different bones + joints which the different muscles must push along and through -- changing the proportions of range-of-motion and force among different muscles -- or which segment of the range-of-motion is used.

• varying the timing and intensity of different phases of different kinds of pushing.

e.g. start the main Extension push earlier while the foot is not far from the hip and make it longer -- versus hold back the main push until the foot is out farther from the hip and make it more explosive.

Here's some of the "gear selectors" available for skating:

• "aiming angle" of the foot -- the angle between the overall direction of forward motion and the direction the foot glides on the ground.

Small aiming angle means a larger ratio of overall forward motion distance per stroke to pushing distance (movement of foot relative to opposite hip) per stroke -- suitable for higher speeds. Large aiming angle is better for slower speeds.

This angle is the closest thing in skating to the "gear ratio" of bicycling and wheeled motor vehicles. The ability to use a small aiming angle to enable the leg muscles to keep applying propulsive force at higher speeds is the main thing that makes inline skating faster than quad skating (and of course faster than running). And the main thing in cross-country ski racing that makes "freestyle" Skating on skis faster than Classic striding on flat + gentle terrain on groomed snow.

But this angle is usually more a result of other "gear selection" choices, rather than a "governor" of gear selection.

• forward-backward position of the hip of the next pushing leg at its set-down.

This is controlled mainly by pelvis/hip rotation about vertical axis: whether the non-pushing-side ("next pushing") hip moves forward ("leading") or backward ("lagging") relative to the currently-pushing hip during the current leg-push stroke.

Moving the non-pushing hip forward increases the air resistance and hill-climbing rate, but has little effect on gliding resistance. At high speed the percentage increase in air resistance or hill-climbing rate is pretty small -- because the forward gliding distance per stroke is so many times larger than the distance of relative hip motion. But at very low speed up a steep hill the percentage difference in hill-climbing rate can be large, because the forward glide up the hill per stroke is so small.

Tricky side effect: There's a side-effect to this "gearing" choice -- and it gets tricky with the different timing synchronization options. Moving the non-pushing hip forward or backward also changes the amount of propulsive work thru the current pushing leg -- the amount and sign of the change depends on the timing: If the rotation is synchronized with the main leg-push, then there is little impact on propulsive work, because the relative side-side and relative forward-backard motion is roughly zero at the time of transfer of weight from one foot to the other, so there is no net change in kinetic energy of upper body mass during the leg-push, so the positive and negative changes in force during the stroke roughly cancel each other out. Pelvis/hip rotation only adds or subtracts propulsive work if it is de-synchronized from leg-push. Which gives us four options:

(a) Leading pelvis/hip rotation synchronized with leg-push: Slight increase in overall forward speed, with no added work to sustainably support the increase speed, therefore other muscle moves must work harder -- which they could do anyway even without the rotation, so this option does not help.

(b) Leading pelvis/hip rotation de-synchronized with leg-push: Forward-backward position of non-pushing hip is roughly even with pushing hip, since weight transfer from foot to foot takes place at the mid-point of the move, so no direct effect on overall forward speed. But there is added net positive propulsive work from the rotational move, which indirectly increases sustainable forward speed -- looks like win.

(c) Lagging pelvis/hip rotation de-synchronized with leg-push: Forward-backward position of non-pushing hip is roughly even with pushing hip, since weight transfer from foot to foot takes place at the mid-point of the move, so no direct effect on hill-climbing rate, so required power is just as high. But the lagging rotation subtracts propulsive work. So this option is a loser.

(d) Lagging pelvis/hip rotation synchronized with leg-push: At low speeds there is a substantial percentage decrease in forward speed and hill-climbing rate, so the power required to sustain motion drops, easing the load on skater's cardio-vascular and muscles. But the negative and positive impacts on propulsive work in each leg-stroke roughly cancel out, so there is no significant loss in power supplied. Reduced power demand with the same power supply -- that's how to make it easier for lots of us non-elite skaters to handle climbing hills.

• sideways position of the hip relative to its foot at set-down.

Foot set-down more inside gives more range-of-motion distance to the Out-Sweep muscles: good for more range-of-motion pushing distance to match higher forward speed. Not good for high-force situations which need to emphasize the stronger Extension muscles.

Seated bicycle pedaling does not permit changing the range-of-motion distance between the hip joint and the ball of the foot, because the ball of the foot must follow a fixed path dictated by the pedal and crank.

• angle of knee-flexion at Set-down

The more knee-bend, the larger effective range-of-motion distance for the medial hip-knee rotation move (good for higher speeds). The less knee-bend the smaller effective range-of-motion distance for the medial hip-knee rotation -- good for higher-force situations, like climbing up a steep hill.

• height of pushing hip above ground at end of Phase 1.

the lower the hip, the more range-of-motion distance in the Extension push.

Unlike seated bicycling, standing bicycle pedaling does permit some change of the range-of-motion distance -- by allowing (or forcing) the hip to rise or small during the leg-push.

• passive glide time versus active push time (? versus overlapping active pushes ?)

Passive glide -- with little or no pushing motion outward thru the foot -- gives more time to rest between pushes (perhaps in a configuration where it's easier to support the weight of the upper body). Or it can allow time to prepare ("wind up"?) for a more explosive push needed for a performance situation.

Stopping the foot motion is possible while pedaling a bicycle, but obviously inefficient, since it then requires extra work to re-start the motion of the masses of the foot + lower + upper leg -- normally not needed for bicycle pedaling. But in skating the mass of the foot + lower + upper leg most be stopped and reversed between strokes no matter what -- so it's just a question of how long to stop and how quickly to re-start.

Another possibility in skating is to have a negative gap between pushes. It's fairly normal for ice and inline speedskaters to set down the next foot before the finish of the previous leg-push. The question is whether to try also to start the Out-Sweep push of the next leg during the final phase of the Extension push of the previous leg. (In bicycle pedaling it's fairly normal and obviously effective to overlap active pushing of the two legs.)

• other factors: e.g. changes in angle or position or proportions of range-of-motion between different muscles, or different proportions times spent in different phases, or maximum sideways speed of torso-shoulder side-swing.

In bicycle pedaling, switching positions from seated to standing tends to shift the emphasis from hip-extension muscles to knee-extension muscles. There are also other substantial shifts in proportion and timing possible within standing bicycling, but the constraints of seated pedaling permit only small variations in proportion, and it's not clear if it helps sustainable power much. Nevertheless in most performance situations seated pedaling delivers higher sustained power output than any variation or mix of variations of standing bicycle pedaling.

How these gear selectors can be used to handle some different performance situations:

• higher speed on flat smooth terrain:  smaller aiming angle, leading (or "forward" pelvis/hip rotation, foot set down more inside its hip, low hip position.

• climb steep hill: large aiming angle, lagging (or "backward") pelvis/hip rotation, foot set down more outside its hip.

• slow surface (rough or soft): large aiming angle, leading (or "forward") pelvis/hip rotation.

more . . .

?? [ to be added ]

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