Ken Roberts - - Skating

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speed of Double-push versus Normal-push

date: 07may30

Several time over the last three years I have asked, "Why is Double-push faster than classic single push?" -- and I've come up with reasons. But now I'm thinking that actually

Normal-push can attain higher speed than Double-push: for a very short time.

My reasoning is that looking at inline skate races, the finish sprints are done using Normal-push (class single push). If Double-push were faster then the winners would be doing it. In the 200-meter time trial in the 2004 World Championships, on a roughly 200-meter oval flat course, both the man and the woman did Normal-push on the straight section into the finish. They did not switch to Double-push.

Why is Normal-push faster?

  • N-p does not have the extra friction of the D-p Aim-switch pivot. The friction is larger at higher speeds and higher turnover frequency rates.

  • N-p does not have the gap in pushing of the D-p Aim-switch. The time of the gap is proportionally larger at higher speeds and higher turnover rates.

  • N-p uses the big leg-extension muscles through a longer range-of-motion distance.

  • Since it is easier for N-p to have a higher turnover frequency, N-p gets a higher frequency rate (more repetitions per minute) of the propulsive motions of torso side-swing, arm side-swing, and side-swing of the recovering leg in the air.

Why is Double-push better at reducing strain on muscles, for longer-time performances?

  • D-p spreads the work-load over more muscles: Early in the inward push it can use the "Sweep Inward" muscles (especially hip-adduction + ankle-supination) on the inside of the leg, which push the foot directly sideways inward.

  • D-p uses big leg muscles (especially hip-extension) through a shorter range-of-motion distance, so it can avoid the range-of-motion segments of a muscle which put more strain on it.

Why does Double-push waste less energy?

  • Some of the muscular work in recovering the leg through the air is wasted. Since D-p uses lower turnover frequency rate, it wastes this work at a slower rate.

  • Unless there is very precise timing, some of the muscular work in sideways swinging of the arms and torso are wasted.  Since D-p uses lower turnover frequency rate, it wastes this work at a slower rate.

  • Some work is wasted in "catching" the downward fall of the weight of upper body near the end of each outward leg-push.   Since D-p uses lower turnover frequency rate, it wastes this work at a slower rate.

"reactive force" moves (esp. forward-backward)

I'm coming to think that forward-backward reactive has no significant role which is overall positive for increasing propulsive Work + Power for forward skating speed. (Perhaps it has a positive role for going around curves?)

what do I mean by a "reactive force" move?

"Reactive force" moves (for me) are about how to use muscles and body parts which are farther from the ground-contact point (near the foot) to add propulsive work through the ground-contact point -- additional work which is net positive over the whole stroke-cycle.

Actually all propulsive forces in skating are "reactive" forces, first in the sense that any mechanical force must follow Newton's laws of inertia and action/reaction. Second in the sense that because the moves of skating are so unconstrained (especially compared with seated bicycling), that it's always important to manage the "inertial" forces dealing with acceleration and deceleration of the masses of different body parts that move, and to manage both "ends" of each pushing move, both action and reaction.

A "reactive force" move (for me) is one that requires a third level of concern about inertia and action/reaction -- namely that a relative move of two body parts which adds positive propulsive work in one phase of the skating stroke cycle can have that work later cancelled by negative propulsive work in a different phase -- through operations of Newton's laws of inertia and action/reaction which result in straightforward predictable ways from the initial move -- when the body parts are returned to their original configuration so that they can repeat the same propulsive move.

Most moves of body parts which are farther away from the ground-contact point are "self-cancelling" in their propulsive work -- unless great cleverness and care in timing of the move is used. Most propulsive moves of body parts closer to ground-contact deliver net positive propulsive work over the whole stroke cycle, even if the moves of some body parts are not exactly coordinated with it -- as long as the other moving body parts are not badly mis-coordinated, and not actively coordinated against the move.

Moves of body parts close to ground-contact have a smaller percentage of the body's total mass between those body parts and ground contact, and substantially larger percentage of body's total mass not between those parts and ground-contact. Most skating push moves work by pushing two neighboring body parts apart from each other: one roughly toward ground-contact and the other roughly away from ground-contact. The portion that is moving away from ground-contact is also moving partly forward, since the force thru ground-contact is aimed partly sideways and partly backward. So this pushing move is accelerating a larger percentage of body mass in a forward direction. But the other smaller percentage of body mass does not go in a backward direction -- and not very far in a sideways direction -- because the edge grip or wheel-sideways grip friction opposes that direction.

After this move the parts must be moved back to their original configuration -- in order to be able to repeat the move. Often the moves to "recover" the body parts to their original configuration are negative for propulsive Work (because they are partly backward and/or partly toward the current leg-push direction). But if the total mass of these parts being recovered is a smaller percentage total body mass, then it is unlikely that the negative from the "recovery" moves will be large enough to outweigh the positive propulsive work from the original propulsive moves. These are the moves which I think of as "close enough" to ground-contact so that I feel confident that their recovery will not cancel their original positive work, so I think of them as . . .

"direct push" moves:

  • ankle relative to the ground-contact or ball or toe of its foot.

  • knee relative to its ankle.

  • hip relative to its knee.

There's another pair of body parts which is "far enough" from ground-contact so it's not obviously in the "direct push" category, yet I do not put into the "reactive force" category:

  • one hip relative to the other.

This pair is not "obviously" labeled as a "reactive force" move, because there are at least two dimensions with moves which when done in the most obvious way are not self-cancelling. Partly because in skating some of the key moves of one hip relative to the other are not only symmetrical in recovery, but "self-recovering" -- the propulsive move in one direction is in itself the recovery for the propulsive move in the opposite direction.

The problem with moves even farther away from ground-contact is that a substantially smaller percentage of body mass is being accelerated away from ground-contact than is being held more stable by side-grip friction or edging at ground-contact. So it is very possible -- even likely -- that recovering these parts back to their original configuration will have a large enough mass and speed so that its negative Work nearly equals (or even exceeds) the positive Work from the original propulsive move -- so the move is approximately self-cancelling.

available "reactive force" moves and dimensions

There are the major moves which are "farther" from ground-contact than the two hip joints -- and thus available to deliver net positive work as

"reactive force" moves:

  • the other leg moving in "recovery" while it's up in the air (since while its foot is in the air, the only effective ground-contact is thru the other foot, so force from motions of the leg in the air can be transmitted to ground-contact only if they go thru the two hip joints.

  • torso-shoulder moves relative to the hips.

  • arm-swing moves relative to the shoulder.

There are other smaller "reactive force" moves which are also available, but which will not be considered separately: e.g. head relative to shoulders, hand relative to elbow.

There are three major dimensions for moving these parts:

  • side-to-side

  • upward-downward

  • forward-backward

Side-to-side is usually the easiest dimension to manage for positive propulsive Work, because the main skating pushes by the two legs are pointed toward opposite sides, so there are lots of timing strategies for making a sideways acceleration or deceleration of a body part coincide positively with leg-push propulsion in the appropriate direction.

Upward-downward has lots of timing strategies, but pure vertical is fundamentally not a dimension that contributes directly to propusive Work.

trying to exploit foreward-backward

Foreward-backward motion remains important for the three obvious "direct push" body parts, and can have a positive role with the "debatably direct" hip-to-hip moves.

I suspect the fundamental problem with trying to exploit the foreward-backward moves of "reactive force" body parts is that it is the foreward-backward dimension that makes the most direct contribution to propulsive work. Therefore it's a significant component to all the "direct push" moves. The usual strategy for making a "reactive force" move is not cancelled by its own recovery move is to find one phase in the stroke-cycle where its push along its main dimension is transmitted to the ground, and to another phase where its push along that dimension is not transmitted to the ground.

But a key strategy for the "direct push" moved is to both generate positive work and transmit it to the ground, through a very large percentage of the stoke-cycle. Therefore the forward-backward dimension is effectively transmitted to the ground through most of the stroke-cycle, so it is difficult to find an "open" time segment when the negative aspect of a foreward-backward recovery move will not be transmitted. Even more difficult to find an "open" time segment which coordinates with other constraints on the forward-backward move and its recovery.

The truth is in the details . . .

  • Recovering leg:  The results in the note about set-down timing subtleties show that foreward-backward does not work for the reactive-force moves by the recovering leg up in the air.

  • Torso + Shoulders relative to Hips:  These moves have a significant foreward-backward component only when the torso and back are fairly erect -- which is bad for aerodynamics.  Also these moves require significant engagement of the back-extension muscles -- but these muscles are already under stress from holding the upper body in a somewhat aerodynamic position.

  • Arm + Hands relative to Shoulders:  There just isn't much mass in the arms and hands. And if you do the easy obvious thing of swinging one arm foreward and the other one backward, you get a net foreward-backward motion of mass equal to zero. Swinging both hands forward in unison tends to be disruptive of balance and rhythm of other motions, so it's likely to have more of a side-to-side than forward-backward. Which leaves swinging only one arm forward + backward, but that's even less mass to use to generate reactive force.

Which leads me to: If the only likely net positive work from foreward-backward is so small (from two Arms + Hands making a small foreward-backward motion, or a larger motion by only one Arm) . . .

So it cannot be worth including it in my repetoire of moves -- since I have sideways arm-swing as an alternative. Even if sideways armswing does not deliver quite as much work in certain high speed situations, I just can't justify the mental coordination practice needed to integrate it in my overall motion -- since sideways arm-swing is so much easier to integrate, because it shares similar timing with my other moves.

Oddly I see that some of the fastest ice speedskaters do use side-side motion for torso and recovering leg, but arm-swing is forward-backward with single arm. (Perhaps because it works well with crossovers?)

To me that seems too complicated: learning separate timing for different reactive force parts. And front-back only works if there's a phase where the foot is aiming straight forward -- which does not work for me climbing up steep hills, or using D-p up moderate hills. So perhaps front-back arm-swing is OK for gentle-terrain specialists, but not for "all terrain" skaters like me. Also not for me because I also like snow-skating on long cross-country skis in winter, where setting down straight and then pivoting outward doesn't work.

set-down timing subtleties 3 points

07may28

There are three points of timing around the setting down of the foot which can occur in different ordering depending on the style of skating:

  • Set-down of the foot of the next pushing leg.

  • Aiming the foot just set down to aiming diagonallly significantly away from straight in the direction of the skater's overall forward motion.

  • Lift-up into the air of the foot of the previous pushing leg.

Here's some orderings which can be effective in different skating situations:

  • (a) Simultaneous Set-down with already Aiming-diagonally, then Lift-up of other foot.

  • (b) Set-down, then Lift-up of other foot, then Aiming-diagonally.

  • (c) Set-down, then Aiming-diagonally, then Lift-up of other foot.

  • (d) Lift-up of other foot, then simultaneous Set-down with already Aiming-diagonally.

Analysis of these different orderings:

(a) Simultaneous Set-down with already Aiming-diagonally, then Lift-up.

Simple Normal-push for high-force situations where there isn't time to pivot the aim of the foot, or for skaters who don't want the complexity of pivoting aim.

(b) Set-down, then Lift-up of other foot, then Aiming-diagonally.

Pivot-aim single-push with ordering designed to gain some propulsive Work from the sideways component of the leg Recovery move thru the air. By lifting up the previous pushing foot while the foot just set down is still aiming straight, the sideways component of reactive side-force from starting the mass of the recovering leg moving inward is not transmitted to the ground thru the foot of the newly set-down leg. If the foot were already aiming outward, this force would be negative for propulsion. Then the sideways inward motion of the recovery leg decelerates and stops after the next foot is aiming outward diagonally, the sideways component of reactive force is transmitted to the ground. So there is a net gain in propulsive work from the sideways component of the leg Recovery move -- a gain which could not if the next foot had been set down already aiming diagonally outward.

Note that even more propulsive work would be gained if the foot were aimed diagonally inward, with ordering of this Aiming before Lift-up -- as in (c) for Double-push.

There might also be a way to gain a little propulsive Work from the backward-to-forward component of the move for setting down the foot -- provided that the foot is set down behind and then still after Lift-up of the other previously pushing leg, it retains some forward motion (relative to the hip of the previous pushing leg). Actually there's no need for all (or any) of the acceleration of this forward motion to occur while the foot is up in the air.

But there are some major negative drawbacks with this strategy: (a) The forward motion of the foot just set down must decelerate and stop before the foot is pivoted to aim diagonally toward the outside, which delays the start of its push and adds stroke-cycle time; (b) the farther the foot moves forward before aiming diagonally outward, the less range-of-motion is available for the forward "slice" or "carve" of the big knee-extension muscles; and (c) If most of the forward acceleration is made while the leg is in the air, then the previous pushing foot must be lifted up pretty quickly, so it does not get to spend as much time in the low hip configuration applies a higher proportion of its main Extension force directly into propulsive Work. (Seems clear to me that it's not worth trying.)

Note that even apart from the major drawbacks, there's little point (based on the physics) in exaggerating the backward position of the Recovering leg in the air, or in exaggerating the quickness or speed in bringing the leg forward into set-down, because all that matters is how much forward speed is still retained after the other foot lifts up -- so actually the relevant forward motion can be started (or re-started after stopping) after Set-down. Also giving attention to the backward component of leg recovery tends to contradict the important focus in the final phase of the Extension move on "slicing" or "carving" the foot forward.

(c) Set-down, then Aiming-diagonally, then Lift-up of other foot.

(or Aiming-diagonally could be simultaneous already at Set-down. It makes no difference to the sideways reactive-force Work)

Double-push stroking can obtain maximum exploitation of sideways reactive force from the leg Recovery move -- provided that Lift-up comes after the foot is aiming diagonally to the inside -- and that the stopping of the sideways inward component of the leg's Recovery move thru the air occurs before the start of the other foot's Aim-switch move. In this case the reactive force from starting and acceleration of the sideways component of the Recovery move adds positive propulsive Work to the other leg's In-push, and the deceleration and stopping of the sideways component of the Recovery move adds positive Work to the other leg's main outward push.

Setting down with the foot aiming straight forward before Lift-up makes no contribution to the amount of reactive-force work from the sideways component of leg Recovery. It does allow the pushing hip to spend more time at a lower height from the ground, which increases the proportion of Extension force which goes directly into propulsive Work. And it having it down there already makes it easier to precisely control the angular configuration of the other foot in its outward main push, and to precisely select the timing of pivoting of this foot's aim and the lifting up of the other foot.

Backward-forward reactive-force from leg recovery or setting down in Double-push? The strategy of exploiting backward-forward Recovery for propulsion does not make much sense for Double-push, because it requires some time for the foot to decelerate and stop while neither foot is aiming diagonally toward the side. But the main theme of Double-push is continuity of effective pushing, and effective pushing requires that at least one foot be aimed diagonally.

The only time when neither foot is on the ground aiming diagonally is very briefly during Aim-switch. So the recovering foot would have to start and stop its forward motion in set down very early.

There are major drawbacks to this: (a) The sideway speed of the leg's Recovery move through the air must be slow enough so that the leg can be stopped early so it can be started forward early (without colliding with the other leg) -- but this implies a big reduction in propulsive Work from the sideways of a simply-timed Recovery move in order to obtain a small gain in Work from a tricky-timed set down move; and (b) The work from the backward-forward move is determined by the maximum forward speed, but attaining higher speed requires more time and more distance of forward motion before the foot pivots to aim diagonally -- but the longer time is not there in Double-push because the Aim-switch move is dynamic, and longer forward distance would take range-of-motion away from the forward "slice" or "carve" by the big knee-extension muscles. (Seems clear to me that it's not worth trying.)

(d) Lift-up of other foot, then simultaneous Set-down with already Aiming-diagonally.

Air-borne -- both legs into the air simultaneously. A result of quick explosive Extension pushes in very high-force situations, such as sprinting from a standing start, or sprinting up a short steep hill.

To obtain a high frequency of pushes emphasizing the big strong hip-extension and knee-extension muscles (and de-emphasize the smaller weaker "sweep out directly sideways" muscles), the Extension push must start earlier while the foot is still closer to underneath its hip than it would be in a lower-force situation. So its Extension force is aimed more vertically than in most situations, and its magnitude is much larger than most situations, so the result is different from most situations:  Launching up into the air.

(or the Aiming-diagonally could occur after Set-down -- but normally that wouldn't make sense because this ordering is used mainly in high-force situations where there isn't any extra time or energy available for an extra pivoting move.)

low hip position

07may26

A vertically lower position of the pushing hip in the later phase of its push tends to increase propulsive work, because:

The lower the pushing hip, the farther the hip to ground-contact line is tilted away from vertical, so the more the main leg-extension push-force is directed sideways (directly propulsive) instead of downward (not directly propulsive).

Therefore it's advantageous to get the hip low earlier in its push and then keep it there longer. So it's good to

  • train + develop the muscles and supporting structures to sustain a low position.

  • learn + refine motion patterns to get the hip low quicker.

How low is too low?

  • It's too low if the pushing foot loses grip.

There needs to be enough downward force thru the foot to hold enough friction to transmit the (directly propulsive) sideways force without slipping. The more hip to ground-contact line is tilted away from vertical, the higher the sideways component of force, so the more friction is needed to transmit it. Much of the downward force is from gravity -- the weight of the skater's legs and upper body -- but this is less if the other foot has been set down in a supporting role. The rest is from the force of the push itself.

So when grip friction is lower (like on wet asphalt) the pushing hip cannot go as low, and the other leg cannot provide as much support.

  • It's too low if the leg muscles + tendons cannot handle it sustainably.

Lower is more strenuous on the leg muscles and tendons -- especially those related to knee-extension. Believing in the importance of getting low is easy. What matters is the hard part: to develop the bodily structures to sustain it. At the time of the final sprint, it does not need to be sustained for so long, so racers tend to get their hips lower then.

Configuration for low pushing hip:

These are the aspects of bodily configuration that get the pushing hip lower:

  • other leg is more flexed in its knee joint.

This is usually the most strenuous aspect. So if you do not want the pushing hip so low, the easiest way is to keep the other leg more extended at the knee joint. Keep the leg straighter.

  • other leg is less flexed in its ankle joint (less dorsi-flexion). [ added 07nov2 ]

Flexing the ankle more forward tends to bring the hip forward and upward. Usually it's easier to flex the ankle joint less if set down the foot further forward relative to its hip.

  • other leg's hip-to-ground-contact line is tilted more away from vertical.

Of course this has major implications for the propulsive strategy for the other leg, especially the "set down" position of the next leg. The closer the foot is set down to directly underneath its hip, the higher the hips (other things being equal). The more the next foot is set down either inside or outside from its hip, the more the hip-to-ground-contact line is tilted, so the lower the hips (other things being equal. Here's three cases:

In Double-push, the other foot is often set down a somewhat inside its hip (as opposed to directly underneath), which is easy and allows the current leg's main push to be lower -- but decreases the range-of-motion of the other leg's inward push.

In classic Normal-push in a high-speed situation (e.g. ice speedskating), the other foot is often set down significantly inside its hip, which increases the range-of-motion of the other leg's main outward push. It also puts some strain on the "sweep out sideways" muscles (e.g. hip-abduction) to "catch" the falling weight of the upper body. Which helps explain why elite ice speedskaters tend to have visibly large muscles on the side of their leg.

In Normal-push in a high-force situation (e.g. climbing a steep hill on snow), the other foot is often set down significantly outside its hip, which is easier and demands much less force from the less-strong "sweep out sideways" muscles (e.g. hip-abduction) -- and decreases the range-of-motion of the other leg's main outward push (usually not a bad thing in high-force situations).

  • pelvis is tilted sideways less away from the pushing hip toward the other side -- i.e. the other hip is higher (or at least less low) relative to the pushing hip.

There's a big trade-off on this one, because the hip-extension muscles of the leg finishing its main push can more effectivly push out sideways if the pelvis is tilted sideways more away from it toward the other side -- because that enables more use of the big "gluteus maximus" muscle which is used for hip-extension in the obvious straight forward direction in bicycling and running. Perhaps elite speedskating specialists could somehow radically re-focus their muscular development on other hip-extension muscles that push more sideways, but general athletes are going to favor a configuration which allows them to exploit the big muscles they're already got (and intend to keep).

The trade-off is that if keep the pelvis + hips level the hip-extension force is lower, but a higher proportion of it is directly propulsive because the pushing hip is a little lower. But if tilt the pelvis away so the other hip is lower, the total pushing force is higher from better engaging the gluteus maximus, but a lower proportion of it is directly propulsive because the pushing hip is a little higher (though some portion of the work from the higher force can be exploited for propulsion indirectly later in the other leg's push).

For Double-push the sideways tilting of the pelvis away from the push has a larger benefit, because the next push (inward push by the other leg) also gets more hip-extension force from the tilt. A drawback is that this pelvis tilt tends to encourage starting the torso-shoulder side-swing move too early -- or puts more "isometric" load on some of the back and abdominal muscles to hold back the torso-swing move.

For classic Normal-push the sideways pelvis tilt does not add any benefit to leg-extension by the other leg, rather in high-force situations it might even hinder the early phase of the next leg-push (but more important is the later phase). But it does add force to the torso-shoulder side-swing move, and the timing for that is good if the pelvis + hip tilt slightly "leads" the sideways move of the torso.

Continuing to hold the pushing hip lower for some duration of time is straightforward: Keep supporting it with the other leg as described above. The other approach for more time low is to get there earlier . . . .

Moving the hip low quicker

There's several methods to get the pushing hip low earlier.

  • start in a lower position at Set-down

This fits well with the role of the supporting non-pushing leg as described in the section above -- especially the first method above -- and also fits with one side of the "big trade-off" of the third.

  • do not push it as much higher

A normal (unavoidable?) effect of the leg's Extension push is to move the upper body higher -- because there's always a vertical component of that force. If the Extension push is not started until later in the stroke, then the pushing hip and the mass of the upper body will not be moved as high earlier, and will not need to wait so long before the pushing hip gets lower again.

  • angle its support away when it's higher

The foot and leg best support the hip and the weight of the upper body when the foot is directly underneath its hip. In classic Normal-push, if the foot is set down outside from underneath its hip, the hip will rise less and drop quicker. Even if the foot is first set-down underneath the hip or even inside it, the earlier and more strongly the leg pushes actively sideways (using the "sweep out from underneath" muscles such as hip-abduction and ankle-pronation), the quicker the support will be removed, and weight of the upper body will rise less far and drop down sooner.

Another advantage of Double-push is that the Aim-switch makes it possible to move through the "foot directly underneath its hip" configuration more quickly -- get the foot out to the side so the hip can drop down.

  • pull it lower when there's little negative effect on propulsion.

The phases when there's little impact on propulsion are when the pushing foot is roughly underneath its hip. So that's the moment to relax the knee-extension and ankle-extension muscles and allow gravity do its work. The weight of the upper body compresses the leg, so the pushing hip must drop. To make this even quicker, could use the knee-flexion and ankle-flexion muscles to active assist in pulling the upper body down.

Double-switch Aim-switch phase is an obvious time for this move. The leg is extended during the In-push and raised its hip, so "undo" that extension and raising before the main outward push -- while there's no effect on propulsive work, during the Aim-switch.

For high-speed Normal-push (like ice speedskating), if the foot is set-down inside its hip, then the initial pushing phase uses the "sweep out sideways" (e.g. hip-abduction, ankle-pronation) muscles. As the foot passes underneath its hip (and tends to change from outside edge to inside edge) the hip and knee can drop lower in preparation for the main outward push.

  • ? push it lower when there's little negative effect on propulsion

If the shoulders are dropping while going into a phase where there's little Extension effect on propulsion, if the dropping is stopped this will help push the hip lower (by Newton's Third Law).

But perhaps it's more advantageous to save this move and its effect for some other phase of the stroke. Since the knee-flexion muscles can accomplish the same result, and they have little else to contribute to skating.

how much upper body falling down helps or hurts?

07may25

As the leg-push progresses into its later phases, the pushing foot moves farther out toward the side, away from underneath the upper body -- so the mass of the upper body drops, with increasing speed. The sideways component of its motion can have a clearly propulsive result, but what about the downward component? Is that just wasted energy? How do different skating motion techniques extract propulsive work from it?

How low the pushing hip drops is important for determining the amount of propulsive Work from the leg-push because:

  • the lower it drops, the farther the hip to ground-contact line is tilted away from vertical, so the more the main leg-extension push-force is directed sideways (directly propulsive) instead of downward (not directly propulsive).

  • the lower it drops, the more gravitational potential energy can be converted into the sideways kinetic energy of propulsion.

The problem with allowing the hip to drop lower is that:

  • the lower it drops, the more kinetic energy it gains in the downward direction -- which must be counteracted by real work from the leg-extension muscles of the other leg (to keep the mass of the upper body from falling down onto the ground) -- and much of that work is not propulsive.

?? one advantage of Double-push stroking is that it normally has less negative effect to choose to position the other leg at its Set-down to convert some of this downward kinetic energy into propulsive work.

?? The way it adds propulsive Work is kinda tricky: by giving the muscles of the other leg which just did its Set-down more force to push against -- and what the muscles are pushing against does not move away as quickly. So the muscles operate at higher force but lower speed. If using the "use the big leg-extension muscles more frequently" strategy of double-push, those muscles are good at handling high forces, and they are aimed in a direction for propulsion, so there is some increase in the sustainable rate of propulsive Power.

Based on the strength of the muscles, there is some optimal rate of falling (and height off the ground) which maximized the increase in Power: not enough fall speed and there's not enough to push against, too much speed to too low a height puts too much strain on the muscles to be sustainable.

Double-push has two advantages: (1) the muscles engaged to "catch" the fall are the main leg-extension muscles, big and strong; (2) not as much need to allow the upper body to fall so far, because the theme of Double-push is to increase turnover frequency.

Normal-push has three options for catching the fall of the upper body, and each has a major problem:

(a) setting down the foot significantly inside toward the other side can engage the "Sweep sideways" muscles (e.g. hip-abduction and ankle-pronation muscles) to "catch" the fall, but these muscles are not as strong as the big leg-extension muscles -- and if the leg-extension muscles do try to help in this configuration, they are "aimed" for negative propulsion; or

(b) setting down with the foot roughly underneath the hip engages the strong leg-extension muscles to catch the fall, but they are not aimed in any propulsive direction, so their work is wasted; or

(c) setting down the foot significantly outside from underneath the hip does engage the strong leg-extension muscles, and in a configuration where they are "aimed" for positive propulsion. But this outside Set-down position substantially reduces the range-of-motion distance of the main leg-push. Which might be OK for some high-force high turnover frequency situations, but would result in a reduction in propulsive Work + Power if used in higher-speed situations.

This problem of reducing range-of-motion also occurs in Double-push when using the inward push just after Set-down to "catch" the fall of the upper body. But the inward push is already expected to have a shorter range-of-motion distance -- because the theme of Double-push power is turnover frequency, not range-of-motion.

Second fall in Double-push:

But then in Double-push, at the finish of the inward push, the hip is again dropping low, and this time the same leg must "catch" the fall of the mass of the upper body. But the upper body is not falling as fast, because the inward-push was shorter so it didn't have time to get falling fast. Also the task of "catching" of the fall gets the aid of a short-term "reprieve" by allowing the mass of the head + shoulders to continue to drop a little further while the falling of the mass lower around the hip is getting stopped by the leg-extension muscles -- so the "impact load" of the drop is spread over a larger period of time.

?? another advantage of Double-push is that there's less need to exploit more gravitational potential energy by allowing the leg and hip to start from a lower vertical when raising the mass of the upper body in the first phase of next leg-push to increase the range-of-motion of leg-extension in the vertical direction -- because the theme of Double-push power is turnover frequency, not range-of-motion.

So there's less of that "negative" vertical kinetic energy that needs to be managed -- either by counteracting it or by altering Set-down position to convert some of it into sideways kinetic energy.


speed boots versus fitness boots

SkateLog Forum -- Speedskating forum
Thread: Speed Skates vs Fitness Skates
Subject:  why speed boots are faster
Date: 07may19

[ my analysis on the differences between the two kinds of boots: ]

I think that fitness skate can provide good stability, but it comes with a cost. First the boot must be well-designed for stability, and with the size and model carefully selected to provide a good fit to the skater's foot, especially in terms of heel pocket and related stuff. I've felt that putting a better footbed into my Salomon V Pro2 boots gives me better support for controlling "edging" in my pushing.

Also the high cuff of a (properly fitting) fitness skate could be able to offer more stability than a speedskate boot, if the high buckle or strap is pulled tight. But most of the time I choose to skate with the cuff-strap undone. The drawback of the passive support from a tight high cuff is that it hinders the ability to use some of those "stability" muscles that work the ankle joint to actively push through the wheels sideways.

So one advantage of a speedskate is that it offers the option of using those muscles for stability when needed, or for active pushing when it's effective. Then its stiffness gives better transmission of this sideways pushing force when a skater chooses to use it.

Interesting that two active moves that actually exploit this freedom are: (1) pushing thru the ball of the foot thru the toe-wheel at the finish of the stroke; and (2) ankle-pronation on the main outward push, which exploits the enhanced sideways transmission. Not surprisingly these moves can be observed in videos of winning speedskaters.

I can think of two other advantages of a speed boot:

  • Lighter weight: This should enable higher turnover frequency, which is a strong determiner of higher power output. Provided that the skater works on exploiting the lighter weight by making quicker leg-recovery moves.

  • Stiffer sole: This could offer better transmission of propulsive Work (in Joules) in the obvious main leg-extension push from big leg muscles. On the other hand the softer sole of a fitness boot is elastic, and the main leg-push goes on long enough and stable enough so that there should be a way to get back a large portion of the energy of compressing the sole -- when softer material "rebounds" in the finish of the push - (since that's what "elastic" means in physics).

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Subject: comparing times same day with different skates
Date: 07may23

I tried some informal time trials this evening with my Bont Redback speedskates and two Salomon fitness skates: Pilot V Pro2 and TR Mag Elite. Here's the times I got, in the order it happened:

  • Pilot 2:52

  • Bont 2:49

  • Pilot 2:47

  • Bont 2:50

  • Mag Elite 2:51

Not sure what to make of those results. My Salomon Pilots have 100-84-100-100 wheels and Bont Redbacks have 5x84mm wheels, so one idea is that 100mm wheels are worth more than a stiff boot. (I was rather surprised with my last result on my Mag Elites with 4x80mm wheels.) Another plausible explanation is that I have not yet developed the neuro-muscular coordination to better exploit the advantage of speedskate boots.

why bicycling is faster than skating

SkateLog Forum -- Speedskating forum
Thread: chasing bikes
Subject:  why bicycling is faster
Date: 07may19

Chasing bicycles (I don't race them) is a no-lose proposition: If I can stay with them (or pass them) it's because I'm great. If I can't it's because they're on a bicycle. Strangest thing was doing double-push on a country road somewhere between Padova and Venezia and having an Italian cyclist in his racing suit draft behind me for 15 minutes. The injustice of this did not strike him. Then he said something friendly in a language I don't understand and sped on his way.

I think bicycling is faster because:

(a) big-diameter smooth wheels (not knobby mountain bike tires) have much lower rolling resistance on real-world asphalt. (Skaters could compete better on ultra-smooth hard concrete.)

(b) Bicycling can effectively use muscles at a higher turnover frequency: 80 rpm is easily sustainable by any well-trained cyclist, and sprinters do 120 rpm or more. Skaters cruise more around 40-50 rpm. Double-push uses some leg muscles at double the frequency, which gets them to the higher turnover rates of cycling, but ...

(c) A skillful cyclist engages the knee-flexion (e.g. hamstring) and hip-flexion muscles for propulsive work, which are major muscles often used in other human tasks (e.g. running), but which make very little contribution to skating power. So cycling can engage lots more muscle mass at 80 rpm than skating.

Skating can engage lots of other muscles not usable for cycling propulsion, but most of those are not well-developed from other human activities, and their role in skating does not get its frequency "doubled" by advanced techniques. Double-push doubles the frequency only of the hip-extension (e.g. gluteus) and knee-extension (e.g. quadriceps) muscles -- also used big-time by cycling and at high frequency.

(d) Very little waste of muscular effort in cycling. Almost all the power output of the four main leg muscles used in pedaling goes into propulsion, with little skill required of the cyclist -- unlike skating where some of the work goes into recovery moves, and effectively using many of the muscles for propulsion requires highly developed coordination and balance. And while skating uses muscular effort just to hold the upper body in position, in cycling much of body weight normally rests on the seat and handlebars.

? gearing ? - Skating does offer effective "gearing" options (except for a very low "gear" for handling a steep hill with high rolling resistance).

A mountain bike with a 46-tooth chainring and a 13-tooth cog pedaled at 90 rpm can go 38 km per hour (23 mph). The main reasons for mountain bikes getting passed by non-elite skaters is not gearing, but knobby tires, and that most riders who take a mountain bike on a skatable trail are not very serious mountain bikers.

Ken 

heel-brake with speedskates

SkateLog Forum -- Speedskating forum
thread: Is it me or is it way harder to brake with speed skates?
subject: analysis + several strategies
date: 07apr13

[quote from another SkateLog poster]
I'm getting into more road skating and I need to stop better so I've been working on my braking. I don't know if it's just me or is it much harder to stop with speed skates than with other types

The normal speedskate design is fundamentally much more difficult for heel-brake stopping. There's a couple of reasons, but the biggest problem is the lack of an high (and reasonably stiff) back on the boot that rises well above the ankle joint. There's lots of analysis of the problems on this page: www.roberts-1.com/skate/istop/hb/analysis

Perhaps the most straightforward solution is get really good at some of the non-heel-brake methods of stopping. My opinion is that the normal T-stop is not a strong enough stop for road-skating -- because unexpected things do pop out in front of you sometimes. I think road-skaters need to have a stronger stop available -- like the "forward" T stop -- and there's some other kinds. Learning that kind of stop is going to grind down a set of wheels. I accepted that price. But then I thought if I wanted to be able to execute a strong no-heel-brake stop in an unexpected situation, I needed to practice it regularly. Which means more wheel-grinding on a regular basis. And because I love skating on rolling hills, the cost and hassle of dealing with wheels wearing down soon led me back to ...

Heel-brakes. Which speedskates are not normally designed for. I think the best workaround to adapt them for heel-braking would be an after-market high extension for the back of the boot -- so the back of my lower leg would have something to press back against which would press the heel-brake against the ground. But I haven't seen it and don't know how to make it, so ...

Gatorleash -- www.gatorbackskate.com : I've found this to be a very robust help for my heel-brake, especially on big + steep hills. I definitely recommend it for most people who want to use a heel-brake with speedskates. Funny thing is that I did only a "quickie" installation of my Gatorleash, didn't do all the steps given in the instructions -- planned to "do it right" later if I decided I liked it -- but then my "quickie" setup worked so well that two years later I still haven't gotten around to "doing it right". That's how robust it's been for me.

My only reservation about it is for quick unexpected stopping situations -- because I have to get into a special position before I start using it -- and I found once I didn't have the nerve to do that in an unexpected situation at higher speed.

There's a couple of other tricks with using heel-brakes -- but the good news is that they're much cheaper and quicker to replace than 100mm wheels.

Ken

ankle pronation

SkateLog Forum
Thread: First time skating on 100mm wheels
Subject:  simple paradigm of edging versus ...
Date: 07may3

[quote from another SkateLog poster]
Think of your leg as a lever and your skate/wheels as the pivot point ... weight transfer causes your wheels to transition from side-to-side. Your ankle needs to remain locked to maximize the transfer of power during this transition.

That's one paradigm for the skating leg-push -- and it has the attraction of simplicity. That paradigm would be the whole story if it were really true that "your leg is a lever".

But actually the human leg is pretty complicated. The knee joint might fit the "simple lever" paradigm, but both the ankle and hip joints have multiple degrees of freedom -- fully 3-dimensional, with several different muscle groups that can apply different kinds of torques thru them.

Maybe it's true that your "ankle needs to remain locked" for simplicity of learning, but there's a whole lot of complicated mechanical-engineering analysis that would need to be done to prove it to be the optimal strategy "to maximize the transfer of power".

[quote] Concentrate on a neutral setdown - not inside, not outside - and allow body weight transfer to create the transition from edge to edge.

That's one paradigm: wait for body-weight transfer. Another strategy to make the edge transition more quickly and powerfully is to also use little-appreciated muscles on the side of the leg. Seems to me that some winning ice speedskaters viewed from the front have "thick" legs -- maybe some muscles on the outside of each leg are getting used a lot in their skating.

[quote] No one actually skates like that ...

When I analyzed some videos of elite ice speedskaters (e.g. medal-winners at the Torino 2006 Olympics), it looked to me like some of the medal-winners were making some edging moves with their ankle-pronation and ankle-supination muscles, did not make a "neutral" set-down. (? maybe they've been working on a more complicated paradigm ?)

Ken

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Subject:  why is "collapsed" ankle bad?
Date: 07may7

[quote] the major point being made is that the ankle should not be collapsing either inward or outward ... ... Inline has grip without an edge, but ice blades do not. Regardless, once again the major point is that a skater does not want to achieve edges at the expense of a collapsed ankle.

OK, so here's a photo of some pretty good inline speedskaters with "collapsed" ankles: www.swiss-inline-cup.ch -- the issue here is not grip versus non-grip, or edging versus not edging, it's about the amount of edging (so there's no qualitative distinction between inline and ice on this question).

The "collapsing" of the ankle joint inward from a "straight" position into a pronated position adds propulsive Work in a straightforward way: It converts gravitational potential energy into sideways-backward kinetic energy. Because as the ankle moves inward relative to the wheel-ground contact line, it also moves downward. So all of the skater's body weight above that ankle joint can also move downward. The physical Work released by this downward move is the weight of the skater multiplied by the distance of the drop.

Suppose that the effective distance of the ankle joint from ground contact with 110mm wheels is 20cm. Suppose that the ankle of tilt away from vertical thru the finish of the push is 40 degrees if the ankle is kept "straight" thru the entire leg-push, but 50 degrees if the ankle is first set down straight but is allowed to collapse during the leg-push. Height of ankle off ground is proportional to the cosine of tilt angle: 20 cos 40 versus 20 cos 50, or 15.3cm versus 12.9cm, a drop of 2.4cm. For a 70kg skater, that's 17 Joules of work. With a stroke-cycle turnover frequency of 50 rpm with two ankle "collapses" (one on each side) per stroke, that yields additional propulsive Power of +28 Watts (less some inefficiency).

That's the choice as I'm seeing it: Force your ankle to follow the simplistic old coaching lore versus gain an extra 28 Watts to propel you forward faster.

btw - These extra Watts are not a "free lunch", because the weight of the body must be lifted up again 2.4cm higher before the start of the next push with the other leg.

I think the really key point (in the physics) for most skaters in most situations is not to set down the foot with the ankle already in a pronated position -- because you cannot get any propulsive work from the collapse of the ankle unless it starts out not collapsed.

Ken

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Subject:  ankle-pronation benefit big wheels
From: Ken Roberts Date: 07may10

Another benefit of larger wheels is that they deliver more propulsive Work per stroke from the inward "collapse" of the ankle joint. Since the ankle is 2cm farther from the ground with 100mm wheels versus 80mm, it has more vertical Distance available in which to release gravitational potential energy into kinetic energy.

Also there's more Work that could be added if active sideways pushing by the ankle-pronation muscles is engaged. It's possible that skaters with very strong ankles could deliver more sideways-push Power if the radius of their "lever" were longer. But this gets tricky because it depends on the Torque versus Angular-Speed curve of the ankle-pronation muscles, and trickier because this interacts with the supplemental force of gravity which varies non-linearly over the range-of-motion angle.

Indoor skating: This might help explain why bigger wheels are successful for speedskating indoors. Seems to me that the decrease in rolling resistance on a smooth wooden floor from bigger wheels is not large (compared with how they help roll over the visible irregularities of asphalt outdoors). Maybe the increased power from ankle-pronation is a significant percentage of the indoor advantage of big wheels.

Might also explain why some special lower-to-the-ground boot-frame designs did not demonstrate obviously faster speeds (e.g. Miller?). Should be interesting how some recent low-to-the-ground designs will fare: No doubt lower gives more control, but does it yield more speed?

Quote from another poster:

For maximum power transfer, a skater wants the axis of their ankle to be in a straight line with the axis down the length of their leg at any given time of their push (more or less). I'm sure some skaters skate otherwise. When they start hogging the podium, we will all get busy dissecting their form, and buying DVDs of their winning technique.

I think the winning speedskaters on both ice blades and inline wheels have already been using ankle-pronation to add power for lotsa years. I could start posting photos of well-known winning inline + ice speedskaters showing pronated ankles, but it doesn't seem important, because . . .

It's just what most athletic skaters' neuro-muscular super-computer in their unconscious brain figures out how to do. Does not require intervention from the conscious mind, or coaching suggestions from a rational analytic model over-simplified enough to be understood by the (small) rational conscious part of our brain. The conscious mind believes what is "politically correct", the unconscious muscle-control module does what really works.

What gaining this Power does require is not setting down the foot with the ankle joint already in a pronated configuration. Which is what most coaches teach and focus attention on watching -- and what physics supports (since you cannot gain Work from pronating the ankle during the stroke if it's already pronated before the start).

Ken 

toe push

SkateLog Forum -- Speedskating forum
Thread: Mixing wheels explained
Subject: secret reality of toe-push
Date: 07apr4

[quote from another SkateLog poster]
For most outdoor skaters, the front wheels wear very fast, due in large part to toeing off and to the t-stop

It's nice to see people acknowledging the objective reality of toe-push.

[quote] if you are going to A2A OR The NYC Skate Marathon & NY 100K then you can't help toe a little bit in those hills

Yes, and there's lots of videos of top racers finishing their leg-push with only their toe-wheel pushing against the ground.

Also, what's the reason that lotsa winning ice speedskaters use klap-skates?

My current thinking about heel and toe push is that there's three major options:

  1. "natural" toe-pushing that most uncoached skaters do because it's like running and walking, using the ankle-extension (a.k.a. plantar-flextion) muscles (e.g. calf) to add propulsive work.

  2. "carving forward" with focus on the heel to achieve propulsive work from maximum range-of-motion by the big knee-extension muscles (e.g. quadriceps)

  3. both carving-forward and toe-pushing: first carving with the big knee-extension muscles, than a final "flick" with the ankle-extension muscles.

Seems to me that option 2 is more important than 1 because the knee-extension muscles are bigger. And it's helpful to spend lots of time consciously practicing option 2 (and blocking option 1) -- to overcome the "natural" tendency to fall back into focus on 1. But when you're skating to win a race (rather than a beauty contest), option 3 is often going to be faster than 2 -- because it engages more muscle mass for direct propulsive work.

Ken

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Subject: mental imagery versus objective time + video
Date: 07apr7

[quote] the only way for you to know is to time yourself doing it

Yes I agree with using timing as a way to find out what really works in technique. I remember several times when I was sure some new technique idea was helping me a lot, but there was no significant difference in timing results. (One reservation is that I think sometimes a new technique which works might require a month or more of practice to train specific muscles to work effectively in new ways).

With toe-push there's a special trickiness, because I think it's often performed unconsciously -- so a skater could still be making a final push thru the ball of the foot, even though they're consciously focusing on pushing thru the heel. (I assume that's why some coaches propose removing the toe wheel, to force perception of this unconscious toe-flick move.)

So my point is that the unless a skater is videod from the side during their time-trial, they cannot be sure if they truly eliminated the toe-flick move. So without side-video, their improvement in time by focusing on heel-push only shows that the conscious mental image of heel-push works.

My view is that consciously focusing on pushing thru the ball or toe of the foot is usually a bad idea. I guess the move is too quick and the required coordination of timing is too precise for our conscious mind to handle -- so it should be left to the faster more powerful neuro-muscular control super-computer in our unconscious brain.

Wheel-wear on the toe-wheel is objective physics. Pushing thru the heel is good mental imagery, but not correct physics.

It it's really true in objective physics that blocking out the unconscious final push thru the ball of the foot is faster, then let's have a time trial of:

(a) inline skate with toe-wheel removed versus inline skate with second or middle wheel removed.

(b) ice speedskate with klap-frame versus ice speedskate with non-klap-frame.

Ken

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Thread: Inline speedskating video from 1991!
From: Ken Roberts Date: 07jun1

Thanks for finding such a different kind of video:

Jan Eise Kromkamp 1991 video

Quote from another poster:

Is it my imagination or are they toe-flicking like crazy? guess nobody knew better back then...

I think the pushing thru the toe-wheel is pretty clear in that video. Actually I think lots of speedskaters "knew better" back then and lots of coaches taught against toe-pushing back then -- because toe-pushing is obviously negative for speed on (pre-klap) ice speedskates.

But already back then -- as now -- the unconscious muscle-control module of each fast skater quickly discovered that toe-flick just works on inline skates. It could be that the conscious mind of the racer suppressed that it was happening.

For modern toe-flick, try the two side-view segments in the Pascal Briand perfect double push video. The first segment at video time 0:37 shows toe-flick in his crossovers, the second at time 2:02 shows it in the main outward push of Double-push.

How about the 2002 Central Park (NYC) marathon video -- What do you think about the race leader's style starting around video time 1:30?

My view is that it's still good for most of us to think about pushing thru the heel in our conscious minds, and keep doing heel-push drills to practice the "forward carve".

Ken 

skate Italy

Subject: Torino in Italy
SkateLog forum thread: Which city is most skater friendly?
Date: 07may10

Of the major cities in Italy I've tried so far, Torino / Turin is the one where it was easiest for me to find streets and sidewalks with both a decent rolling surface and interesting environment + views. The problem with lots of famous Italian cities is cobblestones ("sanpietrini" ?). Torino has something different on many of its plazas and sidewalks: really large stones (like 0.5m x 1m, almost 2ft x 4ft) that are fairly smooth. Plus lots of streets with decent asphalt. And interesting structures (some built for the 2006 Olympics?) + parks + shopping districts. And the Po River, I skated over three bridges.

I used the StraTorino 2003 route as a starting concept (linked from this page of Italy skating events), also bought a city street map and used that to add other interesting places to try skating to.

I'd be glad to hear about other ideas for skating in the cities of Italy. (Or outside the cities -- looked like some interesting single-lane asphalt roads in the farm country say 25km north from Torino.)

Milano has lots of well-paved streets, but they tend not to be in the places that I most wanted to see (e.g. central tourist sites + shopping districts). Also I like skating by water, the the canals ("navigli") of Milan didn't compare with the rivers of other great cities. I would bring skates to Roma / Rome again, but cobblestones are a big factor there. The stones of Venezia / Venice might be large enough to be sorta skatable, but didn't look like fun, and lots of pedestrian traffic in narrow places. The obvious city I have not yet seriously considered for skating is Firenze / Florence.

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subject: skate Milan Italy report
date reported: 07feb25

I had a fun time skating on the streets of the city of Milano on a Sunday off-season. I saw two other skaters out rolling in the middle of the day, and lots of mellow bicyclists enjoying just a Sunday ride around the city. I found lots of decently wide streets with fairly smooth asphalt, and lots of smooth sidewalks too, especially away from the city center toward the north.

But near the city center it was difficult for me to avoid the need to skate on some streets + sidewalks with wide stones instead of asphalt -- flat stones around 30cm (12 inch) wide. Fortunately I rolled into only a few places with the smaller cobblestones (“sanpietrini” ?) around 8-12cm (3-4 inch) wide, which are found in Rome and some other cities of Italy (also on a few of the major streets in Paris). I find the larger stones easier to skate on (one reason I bring my 100mm wheels to Europe) -- but still not actually fun.

My impression is that the city of Milano has the largest collection of wider smoother streets I’ve found so far in Italy. Sorta like Paris but without the hills and the river and the Friday Night Skate -- and trickier to get near to the famous tourist sites without getting onto stones. Handling vehicle traffic seemed similar to lots of other western European cities I’ve skated and bicycled in.

Special treat was to skate (slowly) on the smooth marble inside Galleria Vittorio Emanuele II -- and Piazza Il Duomo nearby was also very skatable (but I wouldn’t want to try it in main tourist season). Some streets I especially enjoyed were Corso Europa and Corso Venezia (both near “S. Babila”, a Metro station and a key stop for the bus from Linate airport) -- and away from the center I found lots of other streets that were fun for me.

What are some other places to try skating in Italy?

Some reports of my other explorations so far are linked from this page:

http://www.roberts-1.com/skate/v/more/05a

Ken

"gear-shift" with skates

SkateLog Forum
Subject: other kinds of "gear shift" on skates Date: 07jan31

[quote from another SkateLog poster]
Cadence is your transmission. Plain and simple. You are operating on a fixed gear conveyance and the only way to change gears is to change cadences.

I think there's other ways to change the kind and rate of force + work on skates:

  • Change the angle of the aim of the wheelframe versus the overall direction of forward motion: Larger angle is like lower gear.

  • Change how far inside or outside the foot is set down on the ground -- which changes the "range of motion" length of leg-extension. Setting down more outside tends to make it easier to apply higher average pushing force -- sorta like lower gear.

  • Change how much the torso side-shift opposes the leg-push. More opposition means higher force thru the leg, while side-shift toward the leg-push actually reduces the force thru the leg.

Likely there's some other changes that are sort of like changing the "gear" of the transmission. Seated bicycle pedaling does not have much freedom like those (though pedaling standing has some interesting options).

I suspect there's some interesting ways to play around with combining some of those other changes with different cadence frequencies.

Ken

skate with poles

see also: poles to help push in skating 2006

posted to rec.sport.skating.inline 07jan4:

subject:  skate with ski poles videos

As I keep skating lots with poles, I keep learning more about it.

Out on a windy day, I find out that it's easier to feel good about skating for a distance into a headwind when I've got poles. I don't know if using poles makes me go any faster into a headwind than ducking down low -- but with poling it doesn't feel to be working as hard, and not so demoralizing.

Poling tends not to add much at high speeds on the flat, so then I just tuck the poles under my armpits. But they're a great help in moderate speeds, like climbing hills -- so poling with the arms makes a good complement to skating with the legs.

I've gotten pretty good now at waving at drivers and walkers while holding my pole. A key step for me, since a big part of my road-skating fun is building positive energy with the people around me.

Photo Op: Last week when I was skating from New Jersey into Manhattan, a couple of people asked to have their picture taken with me, and they did. I think they felt like I was some sort of exotic adventurer, skiing throught their homeland. (Never happened to me before I tried skating with poles.)

Ken

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posted to rec.sport.skating.inline 07jan2:

subject:  skate with ski poles videos

I've been continuing to have lots of fun using special cross-country skiing poles while I'm skating out on the streets. It gets me lots of positive attention from onlookers (and some negative) -- more attention and more positive than skating without poles. Using poles to help push feels real fast and strong up hills, and in short sprints into and out from intersections. Burns calories at a higher rate, and makes it easier for me keep skating for a longer time.

I'm coming to think that the only times I'll be skating without my poles are in (some) group skates and on completely flat tours.

Some of the combinations of the pole-pushes and the leg-skate pushes have a fun feel, as well as being fast. I can't send the feeling over the Net, but here's some video clips of what it looks like:
http://roberts-1.com/t/806/wp
The first two videos show the motion technique I'm enjoying most now: Double Double Double -- push with both poles simultaneously, twice per complete stroke cycle of both legs, and with the legs doing Double-push. The third clip shows how it's possible to move pretty well just pushing with the ski poles, with no skating pushes at all.

Below are some notes about poles.

Ken

Rollerski Poles: I don't use normal ski poles designed for snow, because I and lots of asphalt-skiers have found that the tips tend to break off when they get banged into the street surface. Rollerski poles are designed for the repeated hard impact, and they have carbide steel tips which can get a grip on many (but not all) street surfaces. Rubber-tip poles usually don't grip as well on asphalt -- except they work better on smooth concrete (but my legs don't need any help from my poles on smooth concrete). I think about the only thing which can sharpen those carbide steel tips is a diamond file, so that's what I use on them about once for every 2-4 hours of skating with them.

For really serious pushing with the poles, the connection between hands and pole-handle is critical. In serious pushing, much of the force thru the hand goes into the pole-strap, not directly to the pole-handle. So it's important to have good straps that work for your hand shape + size and pushing style (I like the Swix SR94), and to wear gloves or tape critical spots on the hand, or both -- to help prevent blisters or other repetitive-stress injuries. Even with hand-protection, it's still good to start with short sessions of poling for the first few weeks, until the hands develop some calluses for protection -- also gives arm + wrist joints and muscles some time to build up to handle the repeated shock of pole-against-street impacts.

I use the Swix AluLite CT6 aluminum-shaft rollerski poles (? Are they still available ?). They're heavier than most cross-country ski poles for snow, but I haven't had any of the pole-shafts break yet. A couple of times over many days of use, I've broken a tip (because I did something strange with it), but that's a separate replacement part (embedded in a "ferrule"). There are other manufacturers and models of rollerski poles -- I use these Swix poles mainly because my hands work well with the straps they came with. I usually purchase my poles from cross-country ski stores on the Web (since I don't live anywhere near a shop).

Sounds complicated (though not compared with getting a good fit in skate boots) -- but I think the extra power and fun with poles is worth it.

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more . . .

see also

 

concept words: ski skiing snow roberts report reports learn learning

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