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Ken Roberts - - Cross Country Skiing what's heresee also: more ideas + reports on Skating | public discussion | more on Ski Skating rotation: NKT align or less or otherposted to rec.skiing.nordic 07jan30: subject: NKT versus QUB "new skate" [quote from another r.s.n poster] : Perhaps we're talking about a different DVD. The xczone.tv DVD in the "science" series which I saw talked about measurements of the upper body rotation of elite racers, that in some situations on gentle terrain they did more like Quiet Upper Body, but in other situations like steep hills they used substantial upper body rotation, and the women elite racers tended to use more than the men. [quote] ... generally most people twist too much But I heard or saw no mention on the DVD of any measurements of what "most people" do when they skate on skis. My personal observations about "beginners" skating around me is that not many are using KNT (a.k.a "NKT": Nose - Knee - Toe) alignment to "get around and shift weight". Rather it looks to me like most of them are not shifting their weight much by any means. If it were true that most beginners instinctively shift their weight by using Nose - Knee - Toe alignment, then why was it ever thought necessary by some instructors to force them to do special drills with it? [quote] ... generally most people twist too much Since there was no scientific quantifiable model presented (or even mentioned in the DVD) of how upper body motions contributes to force and power in skating propulsion, what reasonable basis could there be for making any assessment of how much rotation is "too much" for any particular skier in any particular situation. If there was no attempt at a model, then how could anyone know that merely normally athletic skaters ought to be using exactly the same amount and same kind of upper body motion as elite super-athletes? For me the big problem with Nose - Knees - Toes alignment is that it completely ignores hips. And the big problem with the "quiet upper body" approach of the old original "new" skate (circa 2000) was that it gave mental energy to paying attention to the upper body (and also ignored the possible active contribution of the hips). Ken __________________________________________ posted to rec.skiing.nordic 07jan31: Subject: Re: NKT versus QUB "new skate" [quote from another r.s.n poster] : But there is another lower speed situation important for racers: climbing up a steep hill. The measurements showed that elite racers use substantial sideways motion of upper body in that situation. The World Cup winners are doing this not because they're "getting away" with some technique flaw which they haven't fixed yet. They do it because it helps add critical propulsive power in that situation -- the physics of how it helps is straightforward. One problem with the lack of knowing and using the positive model of this physics is that the measurement results mentioned in the DVD miss the key driver. The physics says that what determines how much sideways motion of the upper body helps propulsive power is not its magnitude, whether in rotational angle or magnitude of sideways distance. What really matters in the physics of skating propulsion is the quickness of the sideways motion -- the maximum sideways speed of the upper body as it moves from one side to the other. (the rotational angle or magnitude of distance is only a side effect). So the elite racers might be gaining more power from sideways motion of upper body than "average" skaters, even though the slower skaters show a larger magnitude of rotation -- if the elite racers use their better-trained abdominal and spinal muscles to accelerate the mass of their torso quicker. It's also possible that elite racers in situations using higher turnover frequencies might be gaining more power from sideways upper body motion than at lower turnover frequencies, even if the magnitude of the motion were smaller in higher turnover. I say "might" because the DVD did not report any measurements of maximum sideways speed. Instead they just tried to settle some old coaching lore controversy. I don't know if the scientific paper measured speed or quickness. Does anyone have a link to it? [quote] I think the hard part is at intermediate stage when one is contemplating racing and where one has been brought up on a diet of KNT full rotation Is there really anyone left alive who is now starting into racing who was seriously taught that Nose - Knees - Toes alignment was the right way to ski? [quote] then being told by a coach that you have being skiing all wrong. ? I guess that's what makes coaching fun ? Ken __________________________________________ posted to rec.skiing.nordic 07feb9: Subject: Hip or Pelvis rotation: which way? [quote from another r.s.n poster] : The nomenclature of rotating hips + pelvis can be kinda tricky, so I'm not completely sure what's meant here. In response to my previous videos posted a couple of years ago, some smart people suggested that while I'm pushing with my Left leg, I should be advancing my Right hip forward. Some people call this "forward hip rotation" -- though (since hip rotation has another meaning in formal kinesiology) I sometimes prefer to call it "pelvis rotation": like rotating pelvis the about a roughly vertical axis, or about the axis of the spine. The physics of this seems very clear to me: Moving the Right hip forward also moves it further away from the Left ski, which by Newton's Third Law adds Force to my current pushing thru my Left ski. It also sets up my hips and pelvis into position for a maximum "pelvis rotation" or "forward hip rotation" move to add force to my next leg push on the opposite side. So it is simultaneously a direct propulsive move and a recovery move. The physics and biomechanics do not much better than that: a self-recovering move. It also works to add propulsive power for Classic striding on skis and to dryland running and walking. But to me it seems like this move of my Right hip forward while my Left leg is still pushing is tending to turn my hips in the "old" direction, away from the next push, which feels sorta unnatural for skating. But it's the way to take advantage of the physics -- so I've practiced it pretty faithfully for two years. What feels more "natural" for skating is to move the Right hip backward while the Left leg is pushing. That's the natural way to move the hips when practicing KNT / NKT / Nose - Knees - Toes alignment while preparing for and starting the next push thru the Right leg. Assuming that the shoulders are supposed to rotate "naturally" with the Nose, this backward rotational move sorta makes the pelvis align with least tension relative to the Knee and relative to the shoulders and Nose. This "natural" pelvis or hip rotation backwards is the worst thing about using the mental image of KNT / NKT / Nose - Knees - Toes alignment. That's my analysis of the physics: this "natural" backward pelvis (or hip) rotation _absorbs_ propulsive force + work, because it accelerates mass toward the direction of the intended push. Newton's Third Law says that when you do that, you reduce the desired leg-push force. My view is that the rejection of this "natural" rotation of the pelvis was one of the big things the New Skate (original 2000 version) got right. [quote] some people will set up for the next skate by first turning their hips in the new direction. OK, "some people" do that. But I don't think any successful World Cup racers do it. In all the controversy between Borowski and Vordenberg about shoulder rotation and whether the head of an elite racer made a "big loop" or a "little loop", I don't remember anybody claiming they ever found an instance of an elite racer making a "natural" backward rotation of their hips or pelvis. Ken my race report Lake Placid January 27posted to rec.skiing.nordic 07jan28: Bob "highpeaksnordic" wrote: We are hosting the annual NYSEF races this weekend - a 7.5 K skate on Saturday ... When Bob promised I'd race head-to-head against the big names, I didn't guess he was going to deliver on it so personally. In Saturday's Freestyle race we were trading positions for the last lap and more. Then with 300 meters to go I went ahead and thought I had him, but the NY state Criterium Champion can still do it in the last 100 meters, and I had to watch his skis cross the line just in front of mine. Early that morning as Sharon and I were driving up, I was thinking that I didn't want to race ... that I'm not a real racer ... and my real goal for the weekend was to just do a personal time trial of one lap of the Lake Placid Loppet course on Sunday. But I'd had this public conversation with Bob, so now I was kinda stuck doing it. Sharon didn't like the cold cloudy weather, wasn't sure how much she wanted to ski. Fortunately it was a good course at the 1980 Olympic venue, 3 laps of 2.5 km with several steep hills on each lap. But I didn't know much about starting, so I was at the back of my line. I spent the first lap (enjoyably) passing some people in my wave, and then climbing past thrashed junior guys in the previous wave (who perhaps never skied up hills that steep). Likely it was a good thing I started from behind so I hadn't taken the first couple of hills too fast myself. Then I hung on with Bob, and Paul Kuznia from down south encouraged me from the sidelines, but Bob still beat me at the line. After the finish I got talking with a guy in a red suit, and it was Doug Diehl, who a couple of years ago on the r.s.n group had offered a nice tip about double-poling which I practiced lots of times since. When I saw the results I was thrilled to find that my time was only 11% more than Doug's. Also less than a minute behind Joe Korzenecki, who gave me a helpful observation on r.s.n a few years ago about a video of my rollerskiing, along with some face-to-face comments about rollerskis versus inline skatinng that changed my approach. I kinda doubt I'm ever going to finish much better than that against the "North country" racers - (so I guess I better not race any more?) Sharon called and said she'd finished skiing, which turned out to include the whole Porter Mt + Ladies 5K loop. I skied over and met her at the main lodge. I was thinking that since she'd already done her big Mt Van Hoevenberg adventure today, she might want to ski somewhere else on Sunday -- and there was still time in this afternoon for my Loppet lap time trial. So I headed out to Cascade, and it was obvious from the soft cold new snow and the feeling in my legs that I wasn't going to set any personal best. But once I was out there my love of skiing the ups and downs and curves of Porter Mt and the Russian Hill and Ladies 5K took over, and after an hour I found myself skiing into the stadium with a credible V2. Then I missed a turn halfway thru the biathlon side and lost the Loppet course. It struck me I should take this as an opportunity, so I found an easier route back to the lodge and Sharon and finished the day suitably thrashed. (and so on Sunday morning we're driving to Garnet Hill). Ken __________________________________________ posted to rec.skiing.nordic 07jan30: in reply to a question from Andrey: There were three waves, and I finished 19th out of 41 starters in the Seniors / Masters wave, and 3rd out of 6 in my age group. You could say I was "above average" -- How much better does it get than that? And that's "above average" in a pretty serious crew on a serious course. We had some other Mid-Hudson skiers finish well in their waves: like Andrea Palen 7th in the J1/OJ Women and then 6th in the Classic race on Sunday - (Was she in the rollerski group I joined on Butterville Rd back in December?). Nick Mancuso finished 4th in the Classic race J1/OJ Men wave, and looks like he was the fastest J1 that day. head motion in V1 skateposted to rec.skiing.nordic 07jan20: Subject: suggestions for my technique on video [quote from another r.s.n poster] : I worked on doing that for lots of time in my V1 skate up many hills yesterday -- i.e. looking in the direction of my overall direction of forward motion, instead of my current leg-push or pole-push. I found it a bit tricky to move my head differently from my torso + shoulders. As I kept working on it I got much better at it on moderate hills, though I tended to lose it on steep hills. My neck felt a little tired sometimes. This morning I looked at some videos of World Cup racers doing V1 skate up a hill, and here's what I saw: (1) before the pole push, they duck their head down and look toward the side of the pole push. (2) during the second half of the pole push and thru its finish, they raise their head and return it to look straight in the overall direction of forward motion. I think it's a better idea in V1 ("offset") skate to deliberately aim my pole-push diagonally toward the side, in the direction the ski is aimed -- not in the direction of overall forward motion. Looks to me like the elite racers help get that diagonal-sideways aim of their pole push in V1 by also turning their head to the side so it's looking in the same direction they are trying to aim their pole-push. So maybe cross-country skiing is different from bicycling and downhill skiing, and sometimes it's better to look where you're poling instead of looking where you're going? Ken __________________________________________ posted to rec.skiing.nordic 07jan29: [quote from another r.s.n poster] : I think the concept of initiating motion from the hips and lower abdomen while delaying the other parts does not apply to most head motions. I agree that it's advantageous for propulsive power to initiate pushing moves from the core and activate muscles roughly sequentially (with lots of overlap) outward to the hands for poling, or sequentially down to the feet for leg-push. This is because the muscles further out have two roles: (a) adding propulsive work motion of their own; and (b) transmitting propulsive work from other muscles which are not directly connected to the pole or the ski. Since the muscles further out are usually smaller, they cannot
effectively perform both roles simultaneously, so instead they perform them in
sequence: first (b) holding stable and transmitting work from the (usually
bigger) muscles closer to the core, then second after those bigger muscles are
mostly finished with their work motion, comes role (a) adding some work motion
of their own. Ken __________________________________________ [ not posted to any Group ] 07jan22 subject: head motion in V1 skate (and other double-poling) Ducking the head before planting the poles, then raising the head in the midst of the pole-push, adds reactive down-force to the pole-push -- which will normally add a little bit to the overall propulsive power of the stroke-cycle. This point about head motion also applies to most other double-poling situations, including pure double poling and V2 skate. Allowing the head to turn to the side and move together with the shoulders and torso on the poling-side of V1 skate (instead of keeping the head aimed in the direction of overall forward motion) -- will normally add a very little bit to the overall propulsive power of the stroke-cycle. climbing hills: V1 versus herringbone skateposted to rec.skiing.nordic 07jan14: Subject: Hills [quote from another r.s.n poster] : When I look at videos of the World Cup racers climbing up a steep hill, I am struck by how much wider they set down their feet, compared with how they ski on gentler terrain. My explanation is that the muscles from "side-sweeping" out from close underneath (which tend to be on the outside of the leg) are not as strong as the muscles for extending the leg like a piston. Since climbing a steep hill, requires high force, they shift the proportion of their leg-stroke more toward the piston-like leg-extension. Exploiting leg-extension for forward propulsion from skating require that the foot be somewhat out toward the side. If the racers set down close underneath, they'd have to wait until the foot got far enough out so they could gain the high force from leg-extension. But going up a hill, waiting means losing momentum, so instead they just set down the foot further outside. [quote] I end up doing kind of a herringbone/glide, which gets me up the hill ok. Herringbone skate with a single-pole push on each side is an effective way to climb steep hills. I've seen lots of experienced citizen racers use it on steep uphill sections in famous regional and national marathons. You have to make up your mind which is more important: to get to the top of the hill using a simple effective technique that leaves your muscles with energy to enjoy the next hour of skating, or to (hopefully) impress somebody watching for a moment, but then you're left so thrashed at the top that the rest of your skiing is just a struggle. [quote] Same hill with better skaters seem to not faze them at all. There are large variations in power capacity among skiers. There's no point in kidding yourself about where you stand in that range. Perhaps with a well-designed program of training and technique drills you could get to the point where on lots of steep hills you could use V1 instead of herringbone skate. But just pretending that it's true doesn't get you there. Ken __________________________________________ posted to rec.skiing.nordic 07jan16: I like the challenge of trying to make it up tough hills using V1 skate. Like recently I climbed up a very long hill without any pauses to rest (Mill Creek Canyon in Utah, about 445m / 1460 ft vertical of climbing at steepness averaging around 6% grade) (btw I expect I will be able to do that again when I'm 55 years old). I'm convinced that long climb would have been easier if I had used herringbone skate on some of the steeper sections (especially because sometimes the snow was so cold it was like skating on styrofoam). But that wasn't the challenge I took on. Similarly I've usually made it my goal to skate the whole (hilly) 50km Lake Placid Loppet course without using any herringbone skate -- that's just my personal challenge. But I've been beaten by several minutes by other racers who did use herringbone skate up some of the hills. So there's no guarantee that using V1 makes you faster than herringbone skate. I think really effective V1 skate is one of the most complicated methods of human-muscle-powered land propulsion. (I insert "land" only because I'm not sure about the complexity of some swimming strokes). Herringbone skate is much simpler. So my claim is that you ought to have some good reason for taking on the complexity. For me it's "because mastering that complexity is in itself an interesting challenge". Doing V1 up a steep hill to impress other people is a bit tricky. Some observers will think, "Pretty strong to get up that hill using V1 (but kinda slow compared the racers)". Other observers will think, "He's going to his limit on V1 -- too bad he's not smart enough to just switch to herringbone skate". Ken |
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toe-push: push thru ball versus push thru heelposted to xcskiforum 07jan2: forum thread: Pushing off with which part of the foot? Posted: Mon Jan 08, 2007 . . . it's complicated . . . There's at least four different perspectives on this question: (a) mental concept, versus (b) objective physical reality. (c) which phase of the leg-push? (d) a stage in learning technique, versus the finished technique of a World Cup racer. Here's some thoughts about each: (a) There's lots bigger contributors to forward-propulsion work than the possible move of pushing off the ball or toe of the foot. Pushing off the ball feels natural from running, and some of the other more important moves are un-natural. So it's tempting to devote mental attention to pushing off the ball and then miss out on some of those other moves. Thinking about pushing thru the heel seems to help some people to engage some of those other moves -- and often the unconscious neuro-muscular controllers in our brain then activate the appropriate amount of ball-pash move contribution anyway -- even though they were consciously thinking about some different move. (Except that a few people do not unconsciously add a ball-push move.) (b) In every video clip of a World Cup racer I've seen doing V1 skate up a hill, the heel of the foot comes up off the ski before the ski comes up off the snow. Those are videos later than the late 1980s, later than 1995, later than 2000. So whatever their coaches might be telling them, and whatever the racers might be consciously thinking, on video lots of times the World Cup racers look just like they're pushing off the ball of their foot. (c) Thru the roughly the first 70% of the leg-push, it makes sense to have the heel down on the ski, because that's the easiest configuration for transmitting the big forces from the big muscles in the upper leg (hip-extension "glutes", knee-extension "quads", etc.). If using the ankle-extension (a.k.a plantar-flexion) muscles at all, save them for the last part of the leg-push, after most of the big forces have been transmitted. (d) It might well be that many skiers will benefit from going through a long phase in learning technique where they truly eliminate the push-thru-the-ball move, and truly only push thru the heel. Maybe that's a stage that many World Cup racers went through on their way up. But now that they're at the top level, it's not a rule they follow most of the time. (e) Ice speedskating: For decade after decade it was claimed by ice speedskaters that pushing thru the ball would never work. Then in the early 1990s a skate was built that made it possible to do an effective push thru the ball of the foot on ice speedskates. Soon after a whole bunch of world records fell, and then lots of coaches demanded that the new skates be banned, because it was an unfair advantage. The ice speedskaters who won the 5000m and 10000m races in the 2006 Olympics were using skates that enabled effective toe-push. Ken _________________________________________ Posted: Mon Jan 08, 2007 ChrisM wrote: What I see many of us "weekend warriors" doing at local trails is sitting too far back. I find focusing on the ball of the foot results in more dynamic and aggressive technique. Two and three years ago, people would look at videos of my skiing up a hill, and notice that my "butt was down in the bucket" (and they were right). At the same time I compared my videos with elite race videos, and I was shocked to find out that my heel was staying down on the ski the whole time before I lifted the ski off the ground -- but the World Cup racers had their heel obviously coming up off the ski before lift off. My coach then was saying "Don't start thinking about toe-push", but of course I had to wonder, "Seems like the World Cup winners know something I don't." I guess for most people the appropriate toe-push for each situation "comes naturally" from experience running -- but for me it plainly was not happening. So for two years I worked on almost nothing but Legs -- I never imagined I could ski so strongly with no poles. But then two weeks ago I got a video of my V1 skate on rollerskis -- and again I my heel was staying down. But instead of saying, "I've got to remember to do some toe-push at the end of each leg-stroke", I said "What are some larger motion patterns which might be blocking my natural toe or ball-push?" Once I fixed those, an appropriate-looking degree of "toe-off" re-emerged without me needing to consciously think about it. inline skates with poling: nordic inline skatingposted to rec.skiing.nordic 07jan4: Subject: nordic inline skating websites I've just gotten into using my rollerski poles with inline skates (instead of rollerskis), and it's great fun. In a season when for lots of us it's seeming like the future of nordic skiing is going to be more and more off-snow, seemed like it would be good to look at another alternative which focuses less on snow-simulation and more on year-round fun. Seems like lots of people are calling it "nordic blading" (though perhaps that's the name that's getting promoted by the Exel company). Germany: Turns out there's growing interest in this style of off-snow skiing, especially in Germany. I like some of the photos of "nordic skaters" who look better than me: http://www.xc-ski.de/56-Ausrstung-,dataentry_7.htm http://www.xc-ski.de/355-Aktuelles_News_NordicSports-,e_12275,r_2306.htm http://www.pro-nordicwalking.de/nordicblading.html http://www.nordic-bayern.de/links.htm http://www.nordic-plus.de/a/nordicblading.html Netherlands: - with a video: http://www.snow4rest.com/actief/nblading/index.html UK: Here's the most serious native-English-language website I've found so far: http://www.nordic-fitness.co.uk/nordic_blading.html (interesting that they show more locations in the U.K. for "nordic inline skating" than for "rollerskiing") Here's one that reads like a translation from ? Finland or Germany http://www.nordicblading.com/portal/nordic_blading/english/technique/ with some different terms for familiar XC ski skating techniques. Look forward to finding new leads on this. Ken _________________________________________ Date: Friday, January 5 14:42 Thanks for those links -- most helpful to me soon is those K2 ILQ 7 Nordic bearings to make the skate slower -- which are sold separately from the Nordic Trainer skates. I doubt I'd use them for most of the year, but I like the idea of having more resistance around November, so it's not so much of a surprise making the transition from faster asphalt to slower snow. And the slower speed puts more emphasis on poling. . (Right now I'm using 80mm rubber K2 Continental wheels, but I don't think they're manufactured any more, and I just wore out some, and I'd rather have the option of using 100mm wheels -- so putting the resistance in the bearings sounds good). senorfantastico wrote Powerslide has a whole line devoted to it: http://nordic.powerslide.de but described in English, unlike most other German "nordic blading" websites I've seen. I can see how they'd go for the big rubber tires, because in my experienec a significant percentage of the (enormous) network of bicycle trails in Germany (and Switzerland and Austria) are not paved. And rubber tires not being as fast as normal skate wheels provides more opportunities for poling to be useful. (My reaction: Doesn't like like I could do Double-push V2 on those skates.) Another sign of the convergence of XC skiing and inline skating is this claim that K2 was working together with Madshus on boot design for Bjorndalen: www.inlineplanet.com/2006-07/18/radpro.html and that the result is a new and similar cuff design for one of their inline skates. I note that the Madshus website makes the reciprocal claim to have gotten their new XC ski boot design from working with "K2 Skates USA": www.madshus.com/mhtemplates/ProductListBoots.aspx?id=203 W skate on snow videoposted to rec.skiing.nordic 07jan18: subject : W skate on snow video I got Double-push leg stroking working on snow, and Sharon took
a video of it: The poling could use lots of improvement. It was my first time trying it on snow, and I was mainly trying to avoid tripping over the poles with the long skis. _________________________________________ posted to rec.skiing.nordic 07jan18: John Forrest Tomlinson wrote: My wife, who has never read Einar Svensson, said "It's snow dancing." That someone would see something I did on skis as like dancing is a wonderful thing for me. Thanks for sharing it. I always assumed that Einar Swensor sorta borrowed the ski-skating technique titles in his book -- "single dance", "paddle dance", "double dance" -- from Norwegian terminology. I like those terms so much better than most of the others I've heard, but I don't know if they're really Norwegian. I guess W-skate could be called "double double dance". Going airborne with skis and poles is fun. And easier than I expected. Ken _________________________________________ posted to rec.skiing.nordic 07jan18: Jan Gerrit Klok wrote What role will W play in your snow skating, if any? I think I want to work more on the "dancing" aspects. Maybe try to find some new "snow dance" moves that have no utility for propulsion. Anybody got some suggestions? [quote] Will it be a welcome option for selected "open field skate" situations? Or rather for tougher conditions like slow snow and slight uphills? I suspect its advantage (if any) is mainly for acceleration. Unlike skating with poles out on the streets, so far I haven't felt many natural opportunities where acceleration is valuable for me on snow. With other people on snow I'm usually trying to ski together, not get away from them. What are some possible (non-racing) "show off acceleration" opportunities? In situations where I do want acceleration or speed, here's some things I'd consider working on:
The last point is based on the theory that the major benefit of the inward push is to increase sideways weight-shift energy, more than the direct push into the snow. Actually I was surprised that aiming the inward-push ski toward the other side actually worked so easily on snow. Ken _________________________________________ posted to rec.skiing.nordic 07jan18: Camilo wrote: Are you thinking that this is actually a better way to ski? If by "better" you mean faster, I don't know. But I sorta doubt it. It would have to be some very special situation -- likely in a sprint performance. If by "better" you mean something else: like fun to play with; or burns more calories in 10 seconds; or makes people watching wonder what the heck you're doing -- then could be a "better way to ski" sometimes. _________________________________________ posted to rec.skiing.nordic 07jan20: [quote from another r.s.n poster] : Well you're right that "W skate" is not about gliding on a flat ski. And there is some additional frictional loss from edging the ski. The question is whether the additional power from pushing that way is more than the additional frictional loss. In "V1 skate" up a hill there is little or no gliding on a flat ski, and yet elite racers still use V1, so I guess sometimes the additional power is worth it. As for the body moving away from the gliding the ski, that's what Newton's Third Law says is required to happen if you're applying effective pushing force thru the ski. [quote] As you leap off of the ground you are essentially throwing your body in the opposite direction of your ski. The main point of double-push is to increase that opposition of forces in the sideways direction between the body mass and the ski gliding on the snow surface. That "sideways opposition" component is a key difference between W-skate (or "half W") and other jump-skate techniques. [quote] I think when you are watching the races you are seeing the male skiers throwing their body's forward over their skis Not knowing which video segment you're referring to, I'll say that when a ski skating technique includes double pole push, then it definitely helps to get the shoulders forward just before the poles are planted, because then the upper adominal muscles are better "aimed" for pushing partly backwards on the poles. (If the shoulders were more vertically above the hips at the moment of the pole-plant, the upper abdominal muscles would tend to push the poles forward, which hurts rather than helps propulsive work.) Jumping up and landing on the poles also helps add propulsive work to the pole-push. Like in the second half of the third video on this page: http://roberts-1.com/t/806/wp But that's all for poling. For legs in skating, it's definitely advantageous to move the opposite hip forward. But I think it's pretty tricky to derive overall net positive advantage for the skating leg push by moving other body parts forward -- because pretty soon you just have to move them back again to get in position for the next stroke. The physics of skating makes it simpler to gain some net advantage in propulsive power by moving body weight sideways, sorta like "throwing" it from one side and "catching" it on the other, then throwing it back again. And that's the big theme of W-skate. W-skate : hopped Double-push legsposted to rec.skiing.nordic 07jan2: subject: W-skate videos - - Double-push I got Double-push leg stroking working on rollerskis, and Sharon took some
videos of it: "Double-push" leg stroking means that each leg pushes first toward the inside (toward the other leg), and then toward the outside (the usual main skate-push). I like to think that each foot is tracing its own "V" with these two different pushes, so my two legs are doing V + V = W. My approach to making two pushes with the same leg is to make a hop with my foot up in between those two pushes, and switch the aim of the ski while it's (partly?) up in the air. The hop adds some power of its own, but that's not it's main purpose for W-skate. . (On inline skates it's usually not hard to switch the aim by "steering" or pivoting the skate while it stays on the ground -- which is a very effective technique to maintain higher speed in many situations. The W-skate page above has links to video clips of the inline-skate version (no hop) of Double-push -- a technique which has won many inline marathon races.) I'm sure other skiers have done W-skate on snow before -- I'm just supplying a video and an invitation to talk about it. When analyzing the video of the 2006 Olympic Men's Individual Sprint Finals, I saw Bjorn Lind doing a "half W" in the later part of the start zone (on his way to winning the Gold medal). Or at least if he wasn't doing a true "W" then, it was obvious that he's fully capable of doing the W-skate any time he chooses. . (The Gold medal performance of 10000-meter ice speedskating in the 2006 Olympics included some Double-push stroking on ice on the straightaways in the later laps -- Torino was a good place for the showing the extension of Double-push beyond inline skating.) What's this W-skate good for? For me on rollerskis and snow it's just another interesting move to play with. I guess the "half W" might be good for acceleration -- not sure if full W-skate has any advantage for either acceleration or maintaining high speed in any situation on snow. But on wide smooth asphalt with inline skates and rollerski poles, I'm finding Double-push legs combined with V2 poling is awesomely fun and fast -- and the spectators like it too. Ken _________________________________________ Subject: Re: W-skate videos -- Double-push ADK Skier wrote What I noticed from the video is you are really expending a significant amount of energy. Yes, that's how it felt to me doing it. Two reasons: One is that (unlike Double-push on inline or ice skates, and unlike Open Field Skate on skis), I doubt there is any "relaxing" way to do W-skate on snow. Second is that for the video I wanted to show how the two different kinds of pushes could actually help propulsion -- not just prove that it was possible to hop the ski from one edge to the other. Making two serious pushes takes serious energy. But the look on my face might not be from the energy, but from fear. I'm not so comfortable hopping rollerskis that way that I'm not afraid I'm going to land the wrong way or tangle a ski with a pole, and leave some skin and blood on the asphalt. I'm much more comfortable on inline skates, but I'm still new to using them with poles, so even on inlines I'm still afraid of tangling a skate with a pole and going down. Maybe when I try W-skate on snow the fear factor will drop. [quote] elite WC racers still hammer out an explosive V2 in skating generally at the finish. One guess is that's because Bjorn Lind and others like him experimented with W-skate and measured the results -- then concluded that V2 was faster for (nearly?) all of their racing situations. And maybe they concluded that in some race acceleration situations "half W" was better than V2 -- and also better than "full W". On inlines with poles, I really enjoy doing "half W" to accelerate away from a street intersection, with my "fans" at the corner watching. _________________________________________ Subject: Re: W-skate videos -- Double-push It was mostly J Klok's writing about Double-push here on r.s.n that got me to focus on really working on it in the last month -- so thanks a lot to J. Over a year ago I sorta tried it once, and posted to r.s.n a theory of how it should work on snow -- then did nothing to follow up. Turned out the theory was wrong: I guessed that the force of pushing on the poles would make it easier to hop the ski. Actually it's that hopping the ski helps add force to the pole-push. Jan Gerrit Klok wrote hopping seems to be costing more energy that it gives back, even from the extra push. Yes there's surely some inefficiency in building sideways kinetic energy in the in-sweep push, then releasing later into the main outward push. And some greater inefficienty in building greater vertical potential energy and then releasing it with more sudden impact into the pole-push -- inefficiency from the pole basket digging a little deeper in the snow, and from the joints and connective tissue and muscles in the arms absorbing some of the energy. But my suspicion is that the key disadvantage of "hopped" W-skate versus V2 skate is not inefficiency, but something else, or some combination of other things, like (a) it's hard to use significant muscle mass to add more propulsive work while both feet are up in the air, so it inserts a low-power phase in the stroke-cycle; or (b) high peak force required for hopping puts a special "plyometric" stress on some muscles; or (c) aerodynamic drag of higher extended upper body position at higher speeds of a finishing sprint. And I doubt there's one simple reason, efficiency or otherwise, to explain why Bjorn Lind might have used "half W" instead of "full W" in the 2006 Olympics. It's just disciplined experimentation and careful measuring. [quote] When will you be ready to compare a 10-minute double push workout at heartrate X to one with your preferred other skating technique? I was waiting for you to report on that. [quote] A few months from now your hop may be invisible to the naked eye and such internet video's without slow-motion. I doubt that for on snow: Getting a 187cm ski to switch its aiming directions without a substantial hop seems unlikely to me. On rollerskis I doubt I'm going to practice W much more -- because (non-hopped) Double-push V2 on inline skates with poles is just too much fun. _________________________________________ Subject: Re: W-skate videos -- Double-push rm wrote looks like the energy is going up and down rather than mainly forward. Yeah, now that I look at it again, there is a lot of up and down. I notice it especially in the first video with No poling -- because there's no obvious "propulsive" justification for all that vertical motion. Seems like I could have "unweighted" the rollerski enough to switch aiming direction mostly my "retracting" my foot up underneath my hip -- instead of jumping my whole body. The funny thing is that my main intent for the inward push is to generate energy toward the _side_ - (might want to look at the video again with that in mind). Actually my original theory more than a year ago was that Double-push on skis would use minimal jumping of my total body weight -- instead I was planning to make the hop _during_ the pole-push, and use the force on the poles to sorta hold my upper body from falling while I pulled the ski up off the ground for an instant. I suspect that move sequence is possible. But when I tried it, it just felt sorta lame. Not fun, Not powerful. Then I tried "jump V2" (non Double-push), and grasped the synergy of making the hop _before_ the pole-push, which adds force to both the leg-push and the pole-push. And it felt so Fun, so Powerful. And then I saw Bjorn Lind using giant vertical extension with "half W" in the second half of the starting zone in his Gold medal in 2006 Olympics -- so that's what I pursued and refined during the past month. But maybe the "quiet upper body" leg-retraction Double-push would have been better to pursue and refine. More work which could be interesting -- for somebody else. _________________________________________ Subject: Re: W-skate videos -- Double-push Bob L wrote you can see that your hands are out in front when your non-glide ski comes down Thanks for looking so carefully, Bob. Yes I see that I am setting down the other foot before the pole-push finishes. I just compared that with a clip of Christian Zorzi and Per Elofsson, and he holds back setting down the next ski until around when his pole-push finishes. I don't know why I'm rushing it. Something I'd like to work on -- in my V2 skate on skis and my Double-push V2 in inlines -- not just for W-skate on rollerskis. [quote] your pole plant is occurring with your hips down and back rather than "high hip" position. I agree with the observation -- though I do see a slight dropping of the hip before the pole plant in the Zorzi and Elofsson videos. I think the difference is that the elite racers start the compression in their abdomen a little earlier than their hip drip, while I'm starting the two moves simultaneously. So their pole plant occurs a little earlier than mine, so their hips haven't dropped as far as mine. Another thing for me to work on -- in my V2, not just W-skate. [quote] you can get a feeling of Double-push from a ski that is tracking normally and fairly straight. Rather than the ski arcing in and out, which would literallly be double push, your center of mass should travel outward over the glide ski (with the poling motion) then travel back inward on the kick. I think I agree with that. I think the main benefit to the first inward push by the left foot is not that the foot is set down angled inward toward the right, but that it's being used to push (or pull?) the upper body further out toward the left. Then when the left foot switches aim to angle toward the left, it's main outward push force is larger because it's pushing against greater sideways kinetic energy of the upper body. Increasing the sideways kinetic energy of the upper body can be achieved just as well by setting down the ski straight in the line of forward motion. I've noticed this when elite inline marathon racers go up a moderate hill. They no longer have a little "loop" of the skate to the inside. They set down roughly straight, use that "anchor" to pull the upper body further sideways, then pivot the skate out for the main push (and "catch" the sideways momentum of the upper body). Same with Chad Hedrick in ice speedskating in 2006 Olympics. There were only one or two short segments where the NBC commentators replayed to show him actually making a little Double-push inward loop with his ice speedskate. But lots of times in the later laps where he would set down straight and pull the upper body further sideways before "catching" its momentum in the main push. That way he exploits one of the key Force - Work - Power advantages of Double-push, without getting into complications of making fancy S-curves. Ken more . . .see also
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