Skate technique USST two cents
Pete Vordenberg
There is a lot of good technique discussion here and in the US in
general. Most people have hit on what I think is most important –
taking as many ideas as possible, trying them out and deciding for
yourself what works best for you.
Below I posted some clipping from the document Chris Grover and I use
at our regional camps and coaches ed camps. I think they should add
to the discussion nicely.
But first here are some comments on the process of discussing
technique.
The most helpful discussion is one aimed at the ideas themselves –
clarifying them, arguing the merits and downfalls of them and (even
aggressively) suggesting more ideas. Discussion and articles aimed at
discrediting specific people rather than just their ideas is not so
helpful and in fact harmful to our shared cause.
As a positive example Lee Borowski emailed me some years back to
discuss our differences in technique ideas and since then we have made
some headway and I hope produced some material that helps people ski
faster.
One of our biggest obstacles in the US is bringing together what has
been a very fractured ski community. Coming together is important
because we are all working toward the same goal – skiing faster in
general and more specifically helping American's win Olympic and World
Championship medals.
For too long there has been an us-vs-them attitude between different
US clubs/groups and the US Ski Team.
We usst coaches have tried to increase communication with the clubs,
non-usst athletes and general ski community and opened up our camps,
ski, waxing, training and technique ideas as much as we can. We have
also helped as many non-usst top athletes as possible at races and
with training/technique. It isn't perfect but it's a healthy start.
Constructive ideas are always welcome.
The way I see it: US skiing is one body, the USST is one arm of that
body. We need to communicate to function, we need each other to
accomplish anything.
We are not going to win without the help of the US ski community. We
are not going to win without your help.
Here are some things I clipped from a document Chris Grover and I
wrote. By the way when it comes to teaching the fundamentals of
technique, Chris Grover is great. I also highly recommend you all
check out his articles on Core Strength in old additions of The Master
Skier – I think they are online at masterskier.com. You will hear
Kris Freeman say that Core strength has been one of the primary keys
to his results and ability to hold proper body position and technique
through a race. I can vouch for the fact that he is very strong in
the core region. Make core strength a priority – and you will notice
a huge improvement in your skiing.
When we coach our national team athletes we mostly aim to add to their
repertoire of techniques. In most cases (on the national team) we are
not looking to change them in major ways. Most of the major work has
been done. (Kris Freeman is very good at trying new ideas and
adapting to his style the things he thinks will enable him to win
World Cups. His classical and skate technique is a solid starting
model for any and every skier – at least it is a model for the way I
think one should ski – which isn't to say it can't be improved upon).
With less experienced skiers we start with much more basic ideas
(covered below). These are the same principles we use for our
national and development team skiers.
Wendy Wagner is also a great model both for technique (classical and
skate) and as a roll model for all women in sport.
I use Carl Swenson as a model for skating and from him I have
developed many of my ideas – especially his leg work. We have been
friends since the late 80's and it is and always has been the case
that I learn more from him then I try to teach to him.
From the document:
We look at technique from the Podium Level: that is, how does an
athlete have to ski to be the Best in the World? However, good
technique can increase anyone's enjoyment of cross-country skiing!
(I'll add to this that one cannot justify an idea because of a photo
or a video – we cannot rely on imitation if we want to win! Learn
from the best, but don't stop there.)
These technique principles are what Kris Freeman is working on AND
what a beginning skier should be working on. The principles apply to
ALL skiers.
The three most important elements of technique are correct body
position, efficient application of power, and using the correct tempo
for the terrain.
Athletes that arrive in Park City to participate in USST programs are
Applying Power to their skiing (kicking, poling) too slowly in both
skating and classic.
The following is what we are working on in order to win 3 Olympic
Medals in Torino in 2006.
This is taken from the classical portion – can be a problem in skating
as well:
One of the biggest problem young skiers have is over striding – key
words like "ski big," "stretch it out," "glide longer," are misleading
and should be avoided. Skiing big, stretching it out, and gliding
longer are a result of speed, not a cause of it.
Double-Pole
Good double-poling is characterized by a sharp downward crunch of the
stomach muscles. To do this the poles must be in fairly close to the
body and held close to vertical. The hipbone must be forward of the
anklebone, and the upper torso muscles poised over the tops of the
poles at the beginning of the poling phase. Compression of the torso
and arms is simultaneous and the hips quickly return to a high
position.
(Do not fold over – instead, crunch down!)
Double-Pole Power Drill
If the athlete is "sitting" or applying power slowly to the poling
motion, try this drill. To get the body up over the poles, exaggerate
the use of the stomach, and learn to apply power early in the stroke.
Insert 5-10 repetitions where you focus solely on the initial power by
contracting the stomach muscles and striking the asphalt with your
poles with quick force. For this drill, end the push as soon as the
poles hit the ground – arms will not have passed lower than your hips.
The motion is very clipped, quick and powerful. Simply lengthen the
double pole from this drill keeping the same quick application of
force and you're skiing.
Skating Technique
V2
The principles of good body position in skating are the same as they
were for striding, except that the athlete's weight is more evenly
distributed over the whole foot. The poling phase of good V2 skating
should imitate that of the double-pole. The poling motion is combined
with a sharp drop down of the skier's weight (loading the leg muscles)
onto the kicking ski. This initiates the transfer of weight to the
other ski.
Double-Pole Power Drill
This is the same drill we used in classic skiing, with the addition of
V2 timing for the athlete's legs. If the athlete is "sitting" or
applying power slowly to the poling motion, try this drill. To get
the body up over the poles, exaggerate the use of the stomach, and
learn to apply power early in the stroke. Insert 5-10 repetitions
where you focus solely on the initial power by contracting the stomach
muscles and striking the asphalt with your poles with quick force.
For this drill, end the push as soon as the poles hit the ground –
arms will not have passed lower than your hips. The motion is very
clipped, quick and powerful. Simply lengthen the poling motion from
this drill keeping the same quick application of force and you're
skiing.
Double-Pole Power w/ Kick Drill
If the athlete is "falling away" from their kick in V2 (only kicking
with the lower-leg) try this drill. First, focus only on initial
power. As you ski in the V2 technique simultaneously drop your weight
onto the kicking ski and the poles using only the stomach muscles.
Begin and end both the kick and pole motions quickly. Second, after
ten reps, as your speed increases, allow yourself more time to glide,
but keep the short dynamic push. For ten reps, count to three on each
leg before exploding DOWN onto your poles and skis to transfer your
weight to the other ski. Third, as your speed gets higher lengthen
the motion but keep the initial power quick. Eliminate the pause on
each ski – and you're skiing.
V1
The idea in V1 skating is to apply constant power throughout the
technique-cycle and to use the appropriate tempo or length-of-push for
the terrain. We have identified two differing styles of skating: one
is more upper-body centric (think Gunde Svan, Per Elofsson, among
others), the other more lower-body centric (think Skari, Swenson,
Alsgaard, De Zolt, Wagner, Freeman, Zimmerman among others). We feel
that the lower-body centric technique is most effective in steeper
terrain where most people struggle. This technique is characterized a
low body position, and continuous and even power application by the
legs. In gradual terrain (or V2 technique) we teach the more dynamic
upper-body centric style as it involves a larger contribution from the
upper-body. No matter which style of V1 skating is being used, it is
important that the athlete is skating (rather than stepping) up a
hill.
Body Position Drill
If an athlete is "sitting" in their V1, try this drill. Part one:
Start from a stop. With your skis in a V position and weight on both
feet, bend your knees and drop your butt back behind you so your
thighs burn. Tilt forward at the ankles and drive your knees forward
toward the tips of your skis. Your legs should stop burning and you
should roll forward up the hill. Part two: without applying energy
to the kick begin to shift your weight from ski to ski maintaining
this forward, low position. This drill demonstrates the important
contribution of body position to forward momentum in skating.
(the skis push out to the side – not back!)
Hot Feet Drill
Maintain a low, forward position (with or without poles) begin loading
and unloading each foot quickly – as if on hot sand. The feet will
not come together, weight shift will be minimal, tempo will be high
and you will stay in the forward position. This teaches a quick,
light tempo to match tough terrain so you don't bog down. It also
teaches using both legs evenly and not standing up on the non-poling
side leg and stepping off it, but staying low and skating off it. In
V1 there is no offside, no glide side – only two push sides.
(add to this a Nathan Schultz drill that is aimed at accomplishing the
same thing but through different means. Grover also uses a drill like
this and Torin Koos has a good addition as well).
To achieve a good forward driving position with the leg, slow down the
tempo and as the skier puts the ski down, immediately press forward
with the knee. Over emphasise the drive you put into your knee – push
it down and forward toward the tip of your ski and from this position
skate off it to the other ski – do not stand up on that leg.
Watch Carl Swenson do this in a race. You will notice many less
proficient skiers stand up when they put the ski down – especially
those in the "big step" school of skating and the upper-body centric
style (note a bogging down on the non-poling side leg especially in
soft and/or steep terrain).
Torin Koos' variation is to think of running in reverse. Where as a
runner puts the heel down and rolls off the toe, a skier can think of
putting the toe down first and rolling off the heel. This helps keep
the knee driving forward, and keeps the skier from pushing off behind
them – out to the side is better (try this – it works well).
We conclude that:
The previous drills should be worked into any ski or rollerski workout
as a technique check-up.
With technique, it is most effective to focus on one thing at a time
and then quickly tie it into the whole technique and to go back and
fourth like this. Try to incorporate these technique check-up drills
into almost every roller-ski session. They are especially handy to
begin speed sessions or intervals or to add focus to a longer distance
session.
You may notice that in general these drills go from a quick, short
motion to adding more power, to adding speed, to actually skiing.
This is a good way to first learn the correct position, second learn
the correct application of power, and third combine position and power
into proper technique and tempo. In general we go from mechanics, to
power to speed.
To follow up on some other ideas. We do not teach weight shift by
trying to get the skier in a nose-knee-toe position because a skier
can accomplish this position without weight shift by leaning over to
the side and leaving the hips in the middle. Also it can (and often
does) lead to skiers over rotating and swinging too much to the side.
Skiers may accomplish a nose-knee-toe position by doing the right
thing technically but they are not necessarily doing the right thing
technically just because they are in a nose-knee-toe position. The
faster a skier is going the more in line with the ski they will be –
this is because the faster they are going the more down the trail the
ski is moving.
Core strength is vital to skiing fast. Many skiers who over rotate,
swing around and find it helpful to do so are compensating for a
weakness in the core.
I have been talking to Phil Bowen at Gear West about a usst/public
clinic. We give clinics to coaches and juniors nation-wide but maybe
we can do one for the public. Minimal cost. One stop deal is all I
or any of us would have time for – Midwest probably, spring or summer,
maybe fall 2004... Any interest?
BeeCharmer
interested in a clinic in the upper midwest. Gear West would be a
great venue...
chris sauer
ne iowa
Jeff Potter
I'm going to try that KNEE DRIVE idea. The core-strength notion makes
sense, too, which is why I keep throwing the spears and boulders.
Also, I like your reminder of the purpose of US racing: it's part of an
overall connected scene that I like to extend all the way out. Such as:
overall culture > outdoor culture > all US skiers > ski racers > US ski
team > win! No reason to have divided camps. Sure, there's competition at
each step but there's an overall goal that supports an overall scene.
Sounds good to me.
I think that today's openness in the US program---such as with sharing
tech, wax and those timely behind-the-scenes race stories/web-reports
that you put out there---can only help. It sure helps me feel like I'm in
touch.
Such a great change from the way things were!
Best wishes for the podium soon!!!!
--
Jeff Potter
****
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Trukweaz
if you USST guys are going start a series of public clinics...don't forget New
England! Imagine a skate clinic by date and Diconzo's with R Knight by night?
KP
aka The Mog
Erik Brooks
I'm pleased by the 'new openness' of the USST - you go guys!
Erik Brooks,
Seattle
Ken Roberts
finding _something_ to criticize. Here it is:
(1) Physics interpretation of "Body Position Drill" for skating
> This drill demonstrates the important contribution
> of body position to forward momentum in skating.
Physics says that mere body position never contributed any motion to any
skier (who was not on a downhill or in a tailwind). Only current (or recent
previous) work performed by muscles can add to momentum (or even maintain
it).
> Part two: without applying energy to the kick begin
> to shift your weight from ski to ski maintaining this
> forward, low position . . .
> (the skis push out to the side - not back!)
There's nothing wrong with this drill -- it's the interpretation: Shifting
my weight from ski to ski _does_ require me to "apply energy", using first
my hip abductor muscles ("gluteus medius" or something). Those muscles on
the side of my hip can push my whole leg and my ski "out to the side" --
just like Pete says in parentheses.
The difference is "free lunch" versus "specific muscular work" -- and the
reason that difference _matters_ is that specific muscles can be
specifically _trained_ by racers who want to go faster (or easier).
There's a second set of muscles that can be engaged for this exercise of
shifting "weight from ski to ski": The muscles on the side of the abdomen
can "swing" the shoulders even further toward side the skier's weight is
shifting toward. By Newton's Third Law, this side-swing move of the
shoulders generates a "reactive" side-force to opposite direction -- thru
the hips and the opposite leg into the edge of the opposite ski -- to add to
its skate-push into the snow. This extra shoulder-swing move can clearly be
seen in one of Carl Swenson's V1 skate videos (and in the winners of
rollerski races and inline skate races on pavement).
(2) Style on over-rotation
> Many skiers who over rotate, swing around and
> find it helpful to do so are compensating for a
> weakness in the core.
Wishy-washy style.
? "over rotate" ?
Almost leaves the door open to the idea that there could be a _right_ range
of upper-body rotation which is larger than zero.
Ken
Ken Roberts
Whatever happened to "taking risks"? Where did the colorful provocative
stimulations of those original "New Skate" articles go? I didn't find
anything here to get me peeved. I don't even see a sentence that Marty Hall
would be able to pick into to get peeved about, let alone "really peeved".
Instead we get just a bunch of helpful exercises for racers. Hardly worth
the attention of
Pete's race-winning energy level -- if only someone else would offer us
something comparable. (gotta get out now to Mountain Dell and try that Hot
Feet drill.)
Better to be bold and wrong, and provoke conflict and new approaches that
lead to _winning_ -- than to be carefully right . . . and boring.
Ken
Rob Bradlee
--- Ken Roberts <iKen7Robert...@yahoo7.com> wrote:
> I picked through Pete's post sentence by sentence, trying to honor it
> by
> finding _something_ to criticize. Here it is:
>
> (1) Physics interpretation of "Body Position Drill" for skating
> > This drill demonstrates the important contribution
> > of body position to forward momentum in skating.
>
> Physics says that mere body position never contributed any motion to
> any
> skier (who was not on a downhill or in a tailwind). Only current (or
> recent
> previous) work performed by muscles can add to momentum (or even
> maintain
> it).
As a non-physicist I'll offer an explanation that may help. Stand on
your right leg. Let yourself fall to the left. Did that take much
work? Perhaps a TINY amount to get started, but mostly gravity did the
work. Now get up. What Pete is saying is this: let yourself fall onto
the ski. You have to use muscle to hold yourself up, but not to push
off the leg you were on. With the correct body position the ski will
move forward. Now fall onto the other ski. More movement.
I try to get my skiers to do this drill. It's very hard to get people
to stop with the kicking already. Just falling forward and side to
side without a big kick off will move you down the track. It really
helps to watch Zach C. do this.
Regardless of the physics, the essential FEELING is that you are just
falling down the track and moving for free. That's the essential
feeling for going fast in skate skiing.
Rob Bradlee
Philip Nelson
> I picked through Pete's post sentence by sentence, trying to honor it by
> finding _something_ to criticize. Here it is:
>
> (1) Physics interpretation of "Body Position Drill" for skating
>> This drill demonstrates the important contribution
>> of body position to forward momentum in skating.
>
> Physics says that mere body position never contributed any motion to any
> skier (who was not on a downhill or in a tailwind). Only current (or recent
> previous) work performed by muscles can add to momentum (or even maintain
> it).
We argued about this last summer and you're still wrong ;-) From reading
your posts, and from watching your film (very brave of you by the way),
you seem to suffer from the idea that unless muscles are actively pushing,
nothing is happening. This misses two very important points. First, as
Rob Bradlee points out in a separate followup, gravity is an essential
part of the motion and you use energy lifts you back up. Second, the
emphasis Pete talks about for a very quick application of power, rather
than the drawn out affair you both use (from your video) and rationalize
limits the flow of blood to all of your muscles. So, while you may feel
like your doing the right thing because you're working so gosh darn hard,
you may also be starving your muscles of blood flow. Then because of the
body mechanics, you are wasting energy besides. You probably have to work
with a coach to get it started though. No amount of reading or watching
video seems to be able to get people to experience it.
> Wishy-washy style.
> ? "over rotate" ?
> Almost leaves the door open to the idea that there could be a _right_
> range of upper-body rotation which is larger than zero.
You really should look at the ski progressions tape. The rotation is
*not* 0. It' just not exagerated.
Ken Roberts
ski.
Rob Bradlee wrote
> Stand on your right leg. Let yourself fall to the left.
> Did that take much work? Perhaps a TINY amount
> to get started, but mostly gravity did the work.
> Now get up.
Yes, the physics of that make sense. Except that it takes real muscular
work, and not mostly for free from gravity.
Pete Vordenberg wrote about this drill:
> Your legs should stop burning and you
> should roll forward up the hill.
One thing that physics is completely clear about is: You cannot "fall" your
way up a hill without doing hardly any real work.
It's your last "Now get up" move that takes the work. Physics says it takes
real work with specific muscles. The obvious specifically muscles worked
for that "get up" move are the quadriceps muscles in my upper leg.
Bad news, to me. Because my quadriceps muscles _already_ have lots of other
work to keep them busy (and loading them near lactate threshold) in my
skating -- and I bet the same problem applies to most racers' technique
styles.
That's why I like Pete's explanation: "push out to the side" -- because
that's good news to me. Because I can see how to do that -- and practice
getting stronger at it -- without putting more load on my quadriceps.
What I'm saying here is about physics, not mental images. I found it easy
to think directly about the muscle I'm using to do a move, and I like to
sensitize myself to _feel_ the tension in that muscle. But some people find
it easier to visualize the _result_ of a muscular action, and leave the
specific muscle(s) itself unconscious in the cerebellum.
Sounds like in your coaching you've found lots of people who are helped by
the image of "let yourself fall onto the other ski" -- that's good. But I
think different mental pictures work for different people, so I'd suggest
that some coaches might also want to consider teaching Vordenberg's more
_active_ images: "push out to the side", "_shift_ your weight from ski to
ski".
And consider there might be a very few like me who could be helped by a
muscular anatomy lesson about where the hip abductors are located, to start
_feeling_ how they can work to push the ski sideways.
Ken
Ken Roberts
actively pushing for skating up hills.
Philip Nelson wrote
> you seem to suffer from the idea that unless muscles
> are actively pushing, nothing is happening.
Pete Vordenberg wrote:
> The idea in V1 skating is to apply constant power
> throughout the technique-cycle . . . continuous and
> even power application by the legs.
Philip Nelson wrote:
> Pete talks about for a very quick application of power . . .
Huh? Except of that one Hot Feet drill, all the talk about "quick" in
Vordenberg's post was about _poling_. And even the Hot Feet drill continues
on to a variation that starts like this: "To achieve a good forward driving
position with the leg, slow down the tempo . . . "
There was this guy named Thomas Alsgaard who was known for skating with a
_smooth_ style, notably not "quick". But Alsgaard did not seem to suffer
the deleterious results that Philip claims must follow from the "drawn out"
approach. By strange coincidence, Alsgaard using this style achieved better
World Cup race results than anybody on the US National Team, now or ever.
So I'm not feeling embarrassed about my choice of styles -- though I
sometimes am surprised by how poorly I _execute_ some of them in my videos
so far.
Ken
Jeff Potter
> If the athlete is "falling away" from their kick in V2 (only kicking
> with the lower-leg) try this drill.
I have a question about the above. What does 'falling away' and
'lower-leg' mean? A bit fuzzy here.
> First, focus only on initial
> power. As you ski in the V2 technique simultaneously drop your weight
> onto the kicking ski and the poles using only the stomach muscles.
> Begin and end both the kick and pole motions quickly.
Hmmm, does this early snappy kick use bigger, upper leg muscles while
they're over the ski? Is that the idea? And is the idea that when one
doesn't balance on the ski one tends to fall off to the other ski and
have a wishy-washy low-leg kick and miss their chance to kick with the
big upper muscles?
> Second, after
> ten reps, as your speed increases, allow yourself more time to glide,
> but keep the short dynamic push. For ten reps, count to three on each
> leg before exploding DOWN onto your poles and skis to transfer your
> weight to the other ski. Third, as your speed gets higher lengthen
> the motion but keep the initial power quick. Eliminate the pause on
> each ski ? and you're skiing.
>
> [ ] No matter which style of V1 skating is being used, it is
> important that the athlete is skating (rather than stepping) up a
> hill.
This matches for me with a report here I read from someone who watched
inline racers in a hilly marathon and remarked that they didn't seem to
slow down on the uphills or change their technique or body position. No
struggling or stepping: just skated up the hill doing correct technique
same as everywhere else. I bet it applies to snow, too. In my mind
anyway. Someday I'll see how it plays out if I can ever get some ski days
in again! : ) ---We just got a LOVELY LOVELY 8" TODAY! And I groomed my
skate trails in the lovely lovely dark. Didn't need a headlamp. Overcast
but the snow had a nice glow. Saw kids sledding on the hill in the
distance. They had one flashlight and didn't mind the dark most of the
time either. Snow is nice in the dark.
John Forrest Tomlinson
> read from someone who watched
> inline racers in a hilly marathon
> and remarked that they didn't seem to
> slow down on the uphills
Wow, that's great Jeff. Just think how fast we could all be if we
didn't slow down uphill.
JFT
Roger Knight
After months away I stopped back to check out the news group and found
this discussion.....WOW! You know, I think that we should all be
psyched with Pete posting this stuff on here and not attack him(Yes
Ken, that means you). Let me say this: Pete knows more about technique
than any of us. PERIOD. He may not make some video or site famous
skiers who might illustrate his point, but he is up to date on what is
going on. Although we may not have turned out a Thomas Alsgaard
yet(and for those of you who actually believe that Thomas Alsgaard
didn't have a high turnover, you are WRONG! Thomas just looked
smoother because of his size and slightly modified style) we have
shown tremendous progress under the new USST regime. Pete is throwing
himself out there for all of us to take shots at....but does that
really help? Frankly, who are we anyway to go up against him? Pete was
one of the best racers in this country for years....he has seen more
World Cups and great skiers in person(not on some video) than any of
us will ever see. Pete knows what is going on....he might not sit
around and debate the physiology of whether muscles are actually be
used, but is this REALLY important? Really? I mean come on, do you
really actually believe that you know more than Pete? Seriously? This
is his job, and he does it well.....I bet that he has forgotten more
than most of us will ever know about technique....let's be realistis
here.
Pete and others, thanks for the positive flow on this board and in
real life. Don't get bogged down by those who will criticize no matter
what you say....you know better than to listen to this stuff. Keep the
ideas and positive results flowing, otherwise we will never improve as
a country....THANK YOU!
Tim Dudley
Pete has the qualifications and experience. We will all be much poorer if he decides that it's not worth the flak to post to the group. It happened before with Nathan; but fortunately he relented and resumed posting.
I would much rather read what Pete has to say about how to improve my skiing than what Ken has to say - nothing personal, but Pete has the credibility edge. I sincerely hope that he doesn't stop posting. I'm certainly not suggesting that Ken stop posting, but I want to have the choice of who to read, and who not to. I don't want Pete driven off the list.
Tim
15/1/04 12:54, Roger Knight wrote:
bm...@deletethis.d.umn.edu
results by the USST the past few years.
I've been actively thinking about not "skiing big" in my classic
skiing the last couple years and it is good to have that notion
reinforced by you.
This newsgroup, and life in general, is richer due to the diversity of
people/posters. I too give anything written by Ken Roberts nothing
more than a quick skin. I think he'd get more out of a 30-second
instruction session with Vordenberg than he will ever get from his
endless ramblings about the first-principle physics/physiology of ski
technique. But, to each his own.
Cheers,
Brian
... who is very proud of this result (2002 Birkie):
23 Vordenberg, Pete 2:13:36
24 May, Brian 2:14:18
In article <d1ee024b.04011...@posting.google.com>, Roger
Jeff Potter
he means harm. He wants discussion and provocation, but he's not nasty or
anything, just a little teasey. Obviously, who cares if Marty Hall gets
peeved, it's going fast that counts. His analytical bent is harmless,
too...could be helpful to some.
If you ever want to see actually moronic, drive-away, vicious attack types
of posts, see rec.bikes.racing.
It does seem out of place to provoke, tease or be demanding of a busy
coach.
Any other inter/national coaches posting here? Ever? Sheesh! Let's be
grateful...and I'm sure we are.
I'm happy, like so many others here, that Pete decided to share what
they've been doing at the USST. He wasn't signing up for a debate. I'm sure
he knows that. And I likewise hope he keeps on reporting on what they're up
to over there!
PODIUM! PODIUM!
Sly D. Skeez
> Yes, you could do the Body Position Drill by falling down onto the other
> ski.
Is the goal here to ski with technique that looks good, or to ski fast
regardless of how it looks?
Jay Wenner
Griss
> Is the goal here to ski with technique that looks good, or to ski fast
> regardless of how it looks?
>
> Jay Wenner
First, not directed at all to Jay's comment, at all... I'd just like to
chime in to thank Pete for the wonderful post and to repeat what others have
said about not being taken aback by what anyone has posted in "debating"
some of the principles he conveyed.
I'm of the camp that techniques, drills and philosophies by on the snow
experts are worth more (to me) than theoretical musings, no matter how smart
or theoretically knowledgeable the person is. I'd sooner read one post a
year from the likes of Pete than daily posts by an intelligent person who is
just theorizing, but not skiing or coaching at an expert level. It's just
not of interest to me when it doesn't come from an on the snow expert.
Being from a medical background, there's biochemistry, physiology, anatomy,
biophysics, etc, and then there's the human body which defies the rules in
every *individual* case. Science, applied to the human body is in generally
in terms of ranges - not rules. That's why a medical professional gets
better after he/she learns all the exceptions and adaptations and why an
experienced coach who approaches his profession intelligently and
knowledgably, with an understanding of theory, is the expert, not the
scientist. However much theoretical musings will challenge and forward the
sport in the right context; they're just not interesting to me. Also, learn
to pick your battles, don't do it in the face of a real expert who only
posts to be friendly and helpful. He's not looking for a debate and will be
driven off whether you intend this or not. I've seen it in so many
newsgroups.
Second, as to what Jay just said: for a racer, I think the only criterion
is speed, but for some of us the goal can only be to look good. We all know
"really ugly" skiers who are strong, fit and fast and we just wish we could
keep up. When I see Ken's videos I think I probably "look" a lot better but
then hear how $%&ing fast he is (compared to me!). I just think, I wish I
could ski as fast as him regardless of how I look. But, it is also my
opinion, is that world class skiers don't go fast without looking pretty
damn good at least to my semi-educated eye. Maybe not PERFECT from the
theoretician's or even coach's point of view, but man they're within a
gnat's ass of awfully good technique by any standard. There are no truly
ugly world class skiers, in my opinion.
But some of us can't go fast and take a lot of pleasure in at least looking
(and feeling) good on skis - good technique is fun! Case in point: I'm a
pretty old guy (50) who didn't really start skiing for fitness until 3-4
years ago. I'm not a fat couch potato, but I am not really a naturally
strong or fast guy, never have been, and didn't ever do any serious training
during my youth or middle age. Before that I skied, hiked, biked some, but
it was strictly hit and miss, very casual. I bought my first non three-pin
gear (used, second or third tier) striding and skating skis about 6-7 years
ago, and my first top shelf stuff this winter. I entered my first race of
any sort 3 years ago. I did my first 50 k the same year. I do ski as much
as I can now (say 5 hours per week average for 5 months in the winter, which
is a lot for me and really as much as I can possibly squeeze in) and
actually try to follow a informal "program" to properly mix proper LSD and
one day a week of proper intensity. I still creep up "personal bests" in
terms of minutes/km every year and do a 50 k marathon every year, but I'm
SLOW (in the neighborhood of +50% compared to the winners!). What I've
noticed is that my friends who at one time were serious endurance athletes,
given the same state of condition and minutes/km times in the early winter,
improve their times MUCH more quickly given the less time and effort as me
(I pay attention to it and don't think I "overtrain"). I don't know if this
is residual base or genetics (probably both). They also have better
technique than me (especially striding) and so I thank my lucky stars I can
ski with them for a while in the early season - it's really great to ski
with and behind a better skier. Most of the people my speed are very crummy
skiers.
Realistically, with 5 hours per week, at age 50, with the lack of historical
base and genetics, can I continue to increase my fitness, yes. Can I
continually improve technique, yes. Can I enjoy skiing and take pride in my
technique - absolutely yes. Can I be fast (in terms of competing in age
group) regardless of pretty or ugly technique? - no. So it's technique or
nothing as far as being top level at something.
But I really will have modest improvements over time. For example, my goal
is to get another 10+% knocked off my 50K time, over the next couple of
years (I'm at 3:45 and would like to be between 3:15 and 3:30). I don't
expect be competitive with the national-masters level skiers who are in my
age group locally. But EVERY TIME I ski, I ENJOY working on good
technique - not from any theoretical basis, but just trying to emulate what
I _see_ from video clips, and integrate what I read, and occasional lesson
or pointers from people who have real life experience as teachers or
coaches. The theoretical stuff I read here (or used to), doesn't do one bit
of good.
So I guess my point is: for some of us, we really do like looking good in
our skiing (I mean feeling efficient and really feeling the flow, not
dressing snappy -although that's part of it as well) since we don't have a
reasonable expectation to be fast anyway.
Grissy.
John Forrest Tomlinson
I just got the Jenex ski technique video with Zach Caldwell and it seems excellent.
> Let's be
> grateful...and I'm sure we are.
I am.
Thanks to Vordenberg for his note.
JT
Jay Tegeder
like to go out and ski. Yeah, I could be faster if I did everything
the right way. I've been skiing and racing over twenty years though
and at 46, it's no big deal if I finish a minute or two faster in a
50K.
That being said, I don't think you guys need to defend Pete or rip
Ken. I'd suggest staying tuned to Ken's posts in fact. I know Pete and
I think he is the type of guy who enjoys discussion on technique. I
think Borowski was more pissed at Pete's "new skate" theory because it
made what he said obsolete. Marty Hall's column in Ski Trax was meant
to add more to the discussion. I think Pete is the type of coach who
feeds off the discussion and disagreement. That's how the sport
evolves. Marty wants to hear Pete's response to his criticism.
About ten years ago, Steve Gaskill, Mike Gallagher and Lee Borowski
all disagreed with each other on technique in the pages of the Master
Skier. It makes people try new things and is ultimately good for the
sport.
Pete is one of the most cerebral guys in nordic skiing. Like many
here, I would put my faith in what Pete says over the other guys
because he is on the World Cup and he is at the center of the action.
What he says about core strength is enlightening IMHO. Take a look at
Elofsson, Fredriksson and Freeman for example. Their stomachs kind of
jut out. Not like a guy carry a few extra pounds, but like a boxer or
football player. The core strength thing makes a lot of sense to me. I
might even start back with the sit-ups myself.
Jay Tegeder
"On the podium if the right people don't show up!" JT
bm...@deletethis.d.umn.edu wrote in message news:<slrnc0dpa...@bmay.d.umn.edu>...
Mark Drela
> Being from a medical background, there's biochemistry, physiology, anatomy,
> biophysics, etc, and then there's the human body which defies the rules in
> every *individual* case.
Except nobody nobody can defy the rules of physics, no matter
how much authority they have behind them. I have real trouble
accepting technique advice which has no apparent reason to work
from a physics viewpoint, or even a physiology viewpoint.
Any technique approach which aims to make you go faster
must do it through in increase in NET power -- power produced
minus power dissipated, or maybe through reduced air resistance.
Also, aerobic power output is limited mainly by cardiac output,
not by how much muscle mass can be recruited. Much technique
advice that I see appears at odds with these key constraints.
Philip Nelson
> Huh? Except of that one Hot Feet drill, all the talk about "quick" in
> Vordenberg's post was about _poling_. And even the Hot Feet drill continues
> on to a variation that starts like this: "To achieve a good forward driving
> position with the leg, slow down the tempo . . . "
I will spend more time with Pete's post. Here I think he is referring to
how to learn the technique, no? I am mixing the words from a few different
coaches perhaps. But one concept that seems to be consistent among them is
that the powerful crunch down with the poles corresponds with a forward
drive of the knee which is followed by a lateral push to the side. On a
V1, your description gets more an more true the steeper the hill gets.
Quick tempo seems to be the norm in most top level skiers these days,
isn't it?
>
> There was this guy named Thomas Alsgaard who was known for skating with
> a _smooth_ style, notably not "quick". But Alsgaard did not seem to
> suffer the deleterious results that Philip claims must follow from the
> "drawn out" approach. By strange coincidence, Alsgaard using this style
> achieved better World Cup race results than anybody on the US National
> Team, now or ever.
Not sure what you mean by "drawn out." On the smoothness comment though, a
quick application of power doesn't really look jerky on film. It actually
looks really smooth because the motion is short and subtle. Dahlie, in the
film studies my coach showed me as examples, doesn't look jerky at all,
but seems to apply his power very quickly, looking relaxed throughout most
of the stroke. Alsgaard is the same way.
>
> So I'm not feeling embarrassed about my choice of styles -- though I
> sometimes am surprised by how poorly I _execute_ some of them in my
> videos so far.
We all feel the same way!
Derick Fay
>
>> Being from a medical background, there's biochemistry, physiology,
>> anatomy,
>> biophysics, etc, and then there's the human body which defies the
>> rules in
>> every *individual* case.
>
> Except nobody nobody can defy the rules of physics, no matter
> how much authority they have behind them. I have real trouble
> accepting technique advice which has no apparent reason to work
> from a physics viewpoint, or even a physiology viewpoint.
It seems to me that any discussion of physics without some measurement of
the magnitude of the forces involved isn't too helpful. To give a
hypothetical example: if I twist my torso to increase propulsive force by
an average .5%, this may be offset by a 2% average loss on the d/p from
being in a less stable position...or the figures might be reversed. We
just don't know. None of the physics discussion I have seen has had any
measurement of the relative magnitude of the forces applied by different
muscles/movements etc--one sometimes hears figures on the proportion of
upper and lower body, but not much more precise than that. In the absence
of these kinds of measurements, isn't on-snow performance a better means
to evaluate technique recommendations than theoretical deduction?
Ken Roberts
feeling good (Grissy) and looking good (Jay W).
Jay Wenner asked:
> Is the goal here to ski with technique that looks
> good, or to ski fast regardless of how it looks?
Slow: one of my current goals is to learn to skate slow.
On gentle terrain and fast snow, I'm interested in playing with what looks
good sometimes. When skating up a steep hill, the only thing I care about
is making it to the top without suffering lactate pain for the next hour.
My problem is that I'm one of those guys for whom skating up a hill fast
_feels_ good -- powerful and strong -- in that moment. I just don't like
paying the price later.
Therefore, I've been trying to learn how _slow_ I can skate up hills
(regardless of how it looks).
So I spent a lot of time yesterday afternoon at Mountain Dell looking for
skaters plainly slower than me, and then following them up all kinds of
hills -- because they were the proof that it was really possible to go that
much slower and still be skating. And it worked. In my third hour I was
finally able to climb hill after hill without stopping to rest.
Seems to me there's several kinds of "looking good" and "feeling good" --
but that merits a whole other thread of its own.
Ken
Ken Roberts
most of what I've read about exercise physiology says it's more complicated
than that.
Mark Drela wrote
> aerobic power output is limited mainly by cardiac output,
> not by how much muscle mass can be recruited.
If I'm understanding Mark right, this is a key issue in choosing among
techniques. Because if (A) most of us are limited by central VO2max, then
there's little point in looking for more muscles to use -- instead we should
just figure out which subset can most effectively convert VO2 into
forward-motion power, and focus only on those few. But if (B) the
performance limit for most of us is something like Lactate Threshold with a
strong "peripheral" component, then looking for more muscle groups to engage
is good, even if somewhat less effective (provided they don't interfere with
the more effective subset).
My current analysis:
It may be that elite XC ski racers are limited by their central
cardio-vascular capacity (heart chamber volume, max rate, central
artery-vein capacity) -- but most of the rest of us are not operating
anywhere near our personal genetically possible VO2max, and certainly not in
a 50 km marathon race.
Lots of authorities say that the aerobic limit for most of the rest of us is
strongly influenced by how well-trained our body is at transporting that
oxygen out to the specific muscles that need it. And that "peripheral"
capacity depends on lots and lots of tiny capillaries out there right near
those specific muscles -- also on how good the specific muscles are at
quickly and effectively using the oxygen that arrives, and quickly and
effectively transporting bad byproducts out ("lactate" seems to be the prime
offender that the authorities mention). My reading says that (B) is the
condition for most of us.
So spending time building those peripheral capacities makes sense, and all
the programs I've seen in books devote lots of training hours to exercises
for that. And to me, finding clever ways to use more muscles make sense --
and when I look carefully at videos of Alsgaard and Swenson skating, I see
them making very precise use of a large number of muscles.
I don't see how the elite XC ski racers could have _trained_ themselves to
such a high VO2max central cardio-vascular capacity without having figured
out how to recruit a larger muscle mass. Same for the rest of us: the more
muscles we learn to engage in our skiing, the more stimulus we can provide
to raise our central CV capacity to higher levels.
That's my current theory anyway -- if somebody's got corrections or
improvement, I'd be glad to hear them, so I can do better on my technique
and training choices.
Ken
Ken Roberts
> if I twist my torso to increase propulsive force by
> an average .5%, this may be offset by a 2% average
> loss on the d/p from being in a less stable position . . .
> or the figures might be reversed. We just don't know.
That's why it's important to delay the twist of the torso until _after_ the
main part of the pole-push motion -- in both V1 (poling-side only) and V2.
So even with no force numbers, it's a reasonable guess that the interference
with the effectiveness of the pole-push is small -- though of course like
Derick says, it's not proof.
Then I look at several elite racer videos with single-frame-step, and I see
precise confirmation of that guess: The racers delay the twist of their
torso in both V1 (poling-side only) and V2, but on the non-poling side of
their V1, the elite racers start the torso twist immediately (because
there's no pole-push to interfere with).
Next I try it myself on rollerskis, and on snow, and the delayed torso-twist
move just _feels_ stronger than "quiet upper body". After that, if I still
needed more proof, I would do measured personal time trials (not for this
move, but I did some for the "forward step").
> In the absence of these kinds of measurements, isn't
> on-snow performance a better means to evaluate
> technique recommendations than theoretical deduction?
Sounds good to me.
So where has anyone displayed any sort of controlled time-trial measurements
to justify the "quiet upper body" religion that seems to be sweeping much of
American coaching right now?
Now I'll offer some controlled time-trial experiments on "quiet upper body":
the winners of all the World Cup skate races. The fastest skater on the US
National team in actual World Cup races. The QUB experiment fails on every
criterion.
Using physics is not about relying solely on "theoretical deduction".
> It seems to me that any discussion of physics without
> some measurement of the magnitude of the forces
> involved isn't too helpful.
I put some estimates of force magnitudes up on the web at
http://roberts-1.com/xcski/skate/power_model
Since then I've thought of some improvements to the model, and perhaps a
significant correction -- just haven't gotten around to it. I'd love to see
someone publish something better, but it's a start.
Ken
Janne G
The absolute limmit is normal set by the cardiac output multiplied
by the blood Hb value, but this is in optimal conditions.
Even elite skiers have problems of producing maximal results if they
switch between techniques as classic and skating.
One example is Frode Estil that have tried to do better in skating or
do as good as in classic skiing, measurements of Vo2 uptake differs a lot
between the two tehcnique used, with the skating as the lower one for him.
So clearly this is a more complicated issue than the "cardiac output answer".
Doing sports in inefficient ways normally makes the O2 uptake lower, but sometimes
the athlete have a body composition that make him more efficient in the O2 uptake
point but bad in the mechanical point. This put some more variables
in this technique question, namely the body efficiency in doing things in
some ways and these ways is not the same for everybody and therefore thecnique
is to a degree individual.
I do agree with Pete that you have to try what works for you and not take it for
granted that how you are doing it today is the best for you, eg experimenting or
trying
new ways of doing things is the way for progress. Technique is not a square rigid
box
of doing things, it is at multi fazetted ball which is elastic and suite all in
it's
own way but to know what's right for you, you have to try new ways of doing thing
and
by that get to know what works for you.
--
Forward in all directions
Janne G
bm...@deletethis.d.umn.edu
Drela wrote:
> Except nobody nobody can defy the rules of physics, no matter
But, people can certainly misapply the rules of physics and get to the
wrong conclusion.
> Any technique approach which aims to make you go faster
> must do it through in increase in NET power -- power produced
> minus power dissipated, or maybe through reduced air resistance.
Ok, let's talk power ...
Unless you finish at a higher elevation, or don't come to a stop after
the finish line, the overall NET power is zero, regardless of how fast
you went around the course. The time integral of power is energy,
assuming you start from rest and finish lying collapsed on the snow
like Bjorn Daehli always used to do, your energy is the same at the
beginning and end of the race, thus, net power is zero. So, let's be
careful with power.
Now at various times, the net power may be non-zero. On a flat
stretch at constant speed, net power is zero. Power produced (by legs
pushing on snow) equals power dissipated (by snow and wind
resistance). On an uphill, there must be positive net power (i.e.,
you have to do work to raise your body up the hill). On a downhill,
there is a net negative power (i.e., you don't do any work, but you do
lose energy to friction). In either case, the net power is non-zero
because elevation (and hence gravitational potential energy) and speed
(and hence kinetic energy) are not constant.
Now assuming our skis are waxed, we've chosen appropriate clothing for
the day's event, we have to follow the set course and we can't change
the viscosity of air, there's not too much we can do about the
dissipative forces, so maybe it's best to think about how we can
maximize power produced by the body (i.e., specifically power related
to forces on snow, not production of heat which doesn't really get us
anywhere). Easy enough, until we realize that we're not going
straight down the trail, we need vectors and all that jazz. Any power
used up to go side-to-side doesn't help us at all, we need to worry
about power being directed down the trail (now this may sound a bit
hokey because power is a scalar, but anyway).
One of the key things that seems to be discussed relatively little is
the angle of the skis, which should be a key variable. If you are
pushing perpendicular to the ski (which you must be doing if you waxed
right and have a "zero-friction" ski), the angle determines a bunch of
things including: component of the force in the along-trail direction
(which helps you), component of the force in the cross-trail direction
(which just rocks you from side to side), component of velocity in the
along-trail direction (which helps you), component of velocity in the
cross-trail direction (which just moves you back and forth across the
trail). It seems to me, based on physics, that for a given frictional
force there is likely an optimal angle of skis that maximizes velocity
down the trail. What is it?
Happy skiing,
Brian
Mark Drela
which touches on the points which have been raised.
I don't remember seeing anyone separate the
power-producing (good) and power-dissipating (bad)
muscle action. The latter plays a big role and is
crucial in efficient free-motion propulsion like skating.
And the potential payoff is very large. People worry
about improving some particular propulsive push from
90% to 91% by some subtle technique change. I'm talking
about changing from -50% to +90% or whatever. Negative
efficiency IS present in the form of the power-dissipating
muscle action, and it's important to identify it and
to minimize it. That's where the payoffs are, I think.
A lot of these points have come up on other forums,
in particular on rec.bicycles.science, and later on
the "Hardcore Bicycle Science" email group. Free-motion
skating propulsion often came up as a contrast to the
forced-motion pedaling propulsion. Optimum skating
angle also came up. A number of the people there
were accomplished physiologists, elite athletes,
engineers, etc, so it was all fairly well grounded
in reality.
----------------------------------
An Approach to Improving Cross-Country Skiing Techniques
Mark Drela
January '04
Here's a different take on the problem of efficient
skiing technique. Almost everyone focuses on increasing
muscle power production. But equally important is reduction
of muscle power dissipation, and I think here where technique
can pay off the most.
First some definitions...
Muscle power production:
Mechanical power produced by a muscle which exerts
a contraction force while decreasing in length.
This is called a "concentric contraction".
Muscle power dissipation:
Mechanical power absorbed by a muscle which exerts
a contraction force while increasing in length.
This is called a "eccentric contraction".
Power is also dissipated by ski friction and air drag,
but these can be treated separately.
First of all, it's not clear that using
more muscles, or using them in some more
clever way (e.g. faster or slower turnover,
shorter or longer stroke, etc) will increase
mechanical power production. In aerobic sports,
the main limitation on power is cardiovascular
output rate. The heart and lungs can put out
oxygenated-blood fuel only so fast, and in
steady state this can be easily consumed
by only a small fraction of all the muscles
available for power generation in skiing,
running, biking, rowing, or whatever.
One consequence if this is that as long as
muscles are well-coordinated and don't
fight each other, the distribution of the power
generation between muscles doesn't seem to
affect the net power output very much.
For example, measurements have shown a wide
variety of force distribution around the pedal
circle between different elite cyclists.
Changing from push-only pedaling to a combination
of push and pull won't significantly change
your steady-state power output in a time trial
(try it!). The naive argument will claim
the pulling up will surely increase power,
because "additional muscles" are used.
But it doesn't work that way. Similarly,
aerobic power output does not seem to be
too sensitive to muscle contraction rates.
Time trial pedaling cadence among different riders
might vary between 75 and 95 rpm. Clearly,
the optimum is very flat.
In skiing, the consequence of all this is that
the details of the power generation is probably
not too important, assuming everything is well
coordinated. For example, if the arms are made
to put out more power, the legs will have to put
out less. A common flaw I see with almost all
ski technique arguments is that they ignore this
"zero sum" cardiovascular constraint. Likewise,
a small change in turnover rate is not likely to
significantly affect power production.
So where to look for problems and improvements in skiing?
As I mentioned in the beginning, one place is to reduce
power dissipated (wasted) by eccentric muscle contraction.
If this is achieved, the net power available for overcoming
ski friction and air resistance HAS TO increase in one way
or another, and you'll go faster. The law of conservation
of energy works.
The most obvious way in which the body dissipates energy
is by using the eccentric contraction to arrest and reverse
body motion. An extreme example is a shadow boxer.
He puts kinetic energy into his arm and glove using
concentric contractions with each thrown punch, only
to absorb it momentarily later with eccentric contractions.
Jumping up and then landing does the same thing.
There is a definite aerobic cost, but he isn't doing
anything that's normally considered useful.
All his aerobic power is dissipated as heat
in his own muscles, rather than in an opponent's chin.
In skating, similar losses occur when the outward motion
of the leg is stopped and reversed immediately after
the ski is lifted from the snow, and then reversed again
just before the ski is set down again. Similar losses
occur with poling arm motions, and upper body motions
during Double Poling.
Some rules for minimizing these losses can be deduced
from basic mechanics. The time-average power dissipated
by any oscillatory motion, whether skating or classical,
is proportional to
P_waste ~ moving_mass * velocity^2 * cycles_per_second
Reducing any of the three things on the right will reduce
wasted muscle power dissipation.
Classical skiing is inherently more dissipative than
skate skiing, simply because the maximum leg velocity
seen by the skier is equal to the skier's forward velocity.
In contrast, the lateral leg velocities in skating are much
slower, so skating wastes less power by this mechanism.
However, unlike the direct push of classical skiing, skating
propulsion has some loss associated with its partly-sideways
propulsive force, which is then partly canceled by friction.
An analysis shows that the skating propulsive efficiency is
1 - Cf/tan(theta)
eff_skate = -----------------
1 + Cf*tan(theta)
where Cf is the effective friction coefficient, including
both friction and snow compaction, and theta is the angle
of the ski from the direction of travel -- small angles
when going fast, large angles when going slow uphill.
The Cf depends greatly on the snow, but can be measured
as the downhill slope required to maintain a slow steady
velocity. My rough guess is
Cf = 0.02 old well-packed snow
Cf = 0.05 fresh soft snow
Here are some calculated efficiency numbers:
theta eff_skate eff_skate
(Cf = 0.02) (Cf = 0.05)
------ ----------- -----------
5 deg 0.77 0.43
10 deg 0.88 0.71
20 deg 0.94 0.85
30 deg 0.95 0.89
40 deg 0.96 0.90
50 deg 0.96 0.90
From these it's clear why we're forced to use a bigger
skating angle on high-friction snow -- the efficiency
is very bad if Cf is big and the angle is too small.
The skating efficiency is maximum when theta = 45-50 degrees,
depending on the exact Cf value. Such angles are used only
on the steepest climbs. So why don't skiers use such angles
all the time? The reason is that large skate angles at
high speed on level ground would require high lateral
leg and ski velocities and fast turnover, which will
unacceptably increase the "shadowboxing" power loss
from the rapid motion reversals. So the optimum skate
angle and associated turnover is a balance between good
skating efficiency and acceptable "shadowboxing" losses.
This will vary with snow conditions -- high-friction snow
favors larger angles and hence a faster turnover.
If we look at the P_waste dependency above, we can deduce
how one might reduce this power loss regardless of the snow
condition. Here are some simple rules:
1) Minimize the mass of the fastest-moving parts (skis, boots, poles).
Light equipment helps. This is somewhat obvious.
2) Once a good skate angle and corresponding lateral velocity
is chosen, try to MINIMIZE turnover rate by bringing each foot
as far in as possible, and extend it as far away sideways
as possible. This is not so obvious.
The revolutionary clap skate in ice speedskating clearly
gives an advantage with rule 2. With the blade still
on the ice, the heel can be lifted off the skate and
a longer push can be achieved using just the toe at
the very end. From photos it's pretty clear that good
XC skaters likewise lift the heel and push with the toe
at the end of the skate stroke.
From the longer leg extension one might conclude that more power
is being produced, but this is unlikely if the skier is already
maxed out aerobically. The real benefit is more likely to be
reduced power dissipation.
3) When arresting motion, try to make the effort do useful work.
For example, during DP, try to give a sharp additional push
on the poles when the torso is nearly at the lowest position.
This will decelerate the torso and transfer some of its
kinetic energy into propulsion, leaving less energy to be
wasted by eccentric muscle contraction when the torso motion
is reversed. I've heard a similar technique should work
in rowing -- a sharp final tug on the oar at the end of the
stroke will put some of the energy of the moving upper body
into propulsion, leaving less energy to be dissipated when
the upper body is returned for the next cycle.
4) Rather than using wasteful eccentric muscle work,
learn to use gravity to reverse motion whenever possible.
For example, the leg at the end of the classical kick
should be relaxed, so it's free to swing back and up
against gravity and then swing back down and forward.
Likewise, let gravity reverse the arm motion as much
as possible by relaxing muscles in the cycle where
appropriate, so the arm coasts up and then back down.
Same goes for DP arm motions. In summary, the ideal
situation is when muscle power is applied only when
the limb is moving in the propulsive direction, and
is relaxed and swinging like a free pendulum at other times.
Good skiers surely use gravity like this instinctively,
but it's good to be aware of what's happening from a physics
viewpoint. Some degree of self-diagnosis and technique
correction can then be performed, which is likely to
be more effective than pure trial and error.
Jeff Potter
> I have real trouble
> accepting technique advice which has no apparent reason to work
> from a physics viewpoint, or even a physiology viewpoint.
Technique advice may well deliver improved physics without us knowing about it. It may seem off
in some way on paper but the various drills and mental imagery might be resulting in good physics
anyway.
When you see "press knee to ski tip" that might appear to be nutty in terms of physics, but in
terms of how the whole human functions in terms of sports it might help you go faster!
There's a lot of impt factors involved, all related to each other---the tech and coach ideas are
meant to boost speed is all, not to try to segregate and explain what's going on in some sense.
Jeff Potter
And we have some cool wax pros here, too.
And some top racers.
We're doin' fine.
Even with the Physics buffs in the crowd.
No, they're all needed, of course.
---But really I meant Inter/Natl *TEAM* coaches. You know, like with a country behind
em.
Jeff Potter
as Pete reports where Kris Freeman (as I recall) was trying to ski like some other
guys. I found that I made a big jump up in my own sports (to winning local things)
when I first discovered that I had my own personal style and stopped imitating
others. I discovered my own special hand that I could play which had its own
strengths. I was neat, also, to not let others dictate races anymore. You go with the
group only to an extent, then you play your hand, your cards, and see what happens.
Obviously to win you have to do something individual at some point! You have to make
what you do YOUR OWN. But I suppose that if you're going to keep moving up you might
go thru many cycles of this: looking at others, at other ideas, then testing them,
then making them your own then seeing if they work. Somehow I don't think they'll
ever work unless you make em yours. And it would be a strange feeling to really feel
at home with a technique but then judge that it's slower and so you give it up.
Ha...people think you have to be ruthless with others in sport. Probably you have to
be most ruthless with yourself: to give up comfortable style things and go into
awkward new waters. The ability to learn... Perhaps the crux!
Janne G wrote:
> I do agree with Pete that you have to try what works for you and not take it for
> granted that how you are doing it today is the best for you, eg experimenting or
> trying
> new ways of doing things is the way for progress.
--
Jeff Potter
> [ ] I'm talking
> about changing from -50% to +90% or whatever. Negative
> efficiency IS present in the form of the power-dissipating
> muscle action, and it's important to identify it and
> to minimize it. That's where the payoffs are, I think.
Maybe that's where relaxation comes in, partly.
I work on technique during the day. But when it comes time for a race
it's funny how it all changes. On the course it's all about doing
whatever it takes to keep the skis flying...and it often includes
techniques with no name and it often includes little thought about
technique at all. At the same time, there's doing whatever it takes to
stay out of the way of the speed: a non-interference policy. Go as fast
as possible. Then try to do zero extra work. Everything except the
speed-moment is total rest. It's quite a funny balancing act! To go as
fast as possible and not blow up.
> [ ] A number of the people there
> were accomplished physiologists, elite athletes,
> engineers, etc, so it was all fairly well grounded
> in reality.
Where's the psychologist and priest? Without including DESIRE,
motivation, drive, we're nowhere. : )
I recall in Mike Muha's website report on his parameters lab-testing that
they rated his "pain threshold" or some such thing. So there's that, too!
As Pete says "Ya gotta want it!" ---Or is that as Sten says...
OK, so you guys DO have some "elite athletes"---they should keep you on
track.
Terje Henriksen
"Pete Vordenberg" <pvord...@ussa.org> skrev i melding
news:eed48266.04011...@posting.google.com...
>
> These technique principles are what Kris Freeman is working on AND
> what a beginning skier should be working on. The principles apply to
> ALL skiers.
>
> The three most important elements of technique are correct body
> position, efficient application of power, and using the correct tempo
> for the terrain.
...and shape.
--
Terje Henriksen
Kirkenes
Sly D. Skeez
> It's great to see on this newsgroup some goals other than racing -- like
> feeling good (Grissy) and looking good (Jay W).
>
> Jay Wenner asked:
> > Is the goal here to ski with technique that looks
> > good, or to ski fast regardless of how it looks?
>
> Slow: one of my current goals is to learn to skate slow.
-When Alsgard was in MPLS, he said something to the effect that the
American's biggest mistake is that they're too worried about
technique.
I guess I should preface this post by saying that I have a very
technical background, pchem, statistical mechanics, plus all the math
and biochem...but I think technical is not the way to learn to ski.
1. The reason I asked the question above, is that I think it's very
possible to skate fairly slow (i.e unable to go faster) with technique
that looks good (but is inefficient), or ski fairly fast with only
fair technique that's very efficient. To skate really fast, you have
to have both good conditioning and good technique, or at least good
enough technique. For classic, you simply have to have good technique,
unless the course rewards double-poling. I think classic skiing really
rewards good technique, but I guess we should define good technique.
-I think it involves more than proper placement of various body parts;
it involves very well coordinated muscle movements and precise timing.
It involves very good balance so the body is not wasting energy
regaining balance and the muslce movements result in efficient
propulsion.
2. Another thing to think about is how the really good skiers learned
to ski with the technique you're trying to copy. I can assure you that
they didn't learn by thinking about physics. I think the good skiers
learn to ski well by skiing a lot and getting some occasional pointers
from coaches.
So an analogy. You copy an artist's painting by precisely trying to
mimick the exact shape of the eyes, the colors used, the quality of
the lines, but the artist (in painting the eyes) was simply trying to
convey anger in the eyes.
Trying to copy the technical aspect doesn't give the same result.
Or maybe golf is better because it involves physical movements. I've
seen many people with beautiful swings, mostly technically correct,
but they score pretty bad. On the other hand, some guys have terrible
swings but the hit the ball well and score well. Their terrible
looking swing works well because it repeats and has good timing,
balance, and power just like a really good player's swing. They also
have good touch like the good players. In golf we call these guys
hustlers.
I think the good skiers learn (practice) to ski with balance and
power, and the tons of skiing gives them good muscle efficiency. Some
of the finer technique points come from coaching. I don't think a
coach can "instruct" a skier to good efficient technique. Much of it
comes from the skier own perception and practice.
Jay Wenner
Ken Roberts
Jay Wenner wrote:
> I think the good skiers learn to ski well by skiing
> a lot and getting some occasional pointers from coaches.
That describes much of how I learn to ski better.
> You copy an artist's painting by precisely trying to
> mimick the exact shape of the eyes, the colors used,
> the quality of the lines, but the artist (in painting the
> eyes) was simply trying to convey anger in the eyes.
Often what I'm trying to do when I look at videos of elite racers is not to
copy the exact movements (e.g. swing my torso 53 degrees left and 48 degrees
right at 53 rpm because that's what I measured Elofsson doing), but rather
to look for deeper physical principles (e.g. use reactive side-force to add
forward-motion power). I don't always succeed in that, because ski skating
is complicated, but I can keep trying to perceive and analyze better. Then
I try to _feel_ the reactive side-force in my actual skiing.
> -When Alsgard was in MPLS, he said something to
> the effect that the American's biggest mistake is that
> they're too worried about technique.
I'm not sure how Alsgaard knows so much about American amateur masters
skiers, but he might be right about the ones he's met in Yellowstone and
Minneapolis. But I am confident that if he had looked at _my_ skiing or my
videos from four weeks ago, he would have pointed out four major technical
improvements for me to work on.
All I know is that in these last six days I'm seeing the fruit -- from
working a lot on specific techniques, getting videos of my skiing taken
about once a week: Every day I'm seeing my skiing get stronger and more
under control. Like today for the first time I skated uphill in ungroomed
soft snow with no poles. But not only was I _able_ to do it for the first
time -- also by coordinating some specific new techniques (new to _me_), I
was able to climb _slowly_ (yet without stalling), and so keep it all going
for a much longer time than I ever imagined I could.
Maybe next year (or next month?) I'll reach the point where I don't think
about technique much any more -- like in my other long-time sports (road
bicycling, ski mountaineering downhill and uphill). But right now it's
pretty exciting.
Ken
Ken Roberts
Mark Drela wrote
> I don't remember seeing anyone separate the
> power-producing (good) and power-dissipating
> (bad) muscle action.
I know that I haven't gone that far in my numerical spreadsheet model --
because it's hard work to generate credible numbers at that level --
especially for a fully three-dimensional motion like skating, where each
major body part has six (non-independent) state variables -- subject to
constraints based on bone-joint geometry, etc.
But I agree that it's worth analyzing conceptually -- to look for big
payoffs.
New Payoff?
A different kind of payoff available in _skating_ is to get positive
forward-motion work out of "power-dissipating" muscle action.
Example: Starting the sideways swing of the torso generates a positively
useful reactive side-force thru the edge of the ski into the snow. But with
proper timing, _stopping_ the torso swing _also_ generates a positively
useful reactive side-force, thru the edge of the _other_ ski (provided that
the skier's body weight has been transferred meanwhile to that next other
ski).
> A common flaw I see with almost all ski
> technique arguments is that they ignore this
> "zero sum" cardiovascular constraint.
I'm open to embracing that constraint -- but I'm still waiting to see some
answers to the multiple arguments I made against it in my Jan 16 post --
especially why it should apply to non-elite athletes in 3-to-6-hour-long
events. And if it's a static "zero-sum", then how come XC skiers often have
higher VO2max than bicyclists?
Mark's new points about this from bicycling are valuable evidence, but: (a)
bicycling is the physically-biomechanically simplest propulsive connection
between human muscles and the external environment, while ski skating is
arguably the most complicated; and (b) if it's really all a zero-sum "wash"
even in bicycling, then how come so many serious bicycle racers are
investing in pedal-force sensors to analyze their stroke cycles?
Several of Mark's other ideas are so interesting, I think they deserve to be
spun off as separate topics.
Ken
Janne G
parts that i will comment on.
"Sly D. Skeez" wrote:
>
> I guess I should preface this post by saying that I have a very
> technical background, pchem, statistical mechanics, plus all the math
> and biochem...but I think technical is not the way to learn to ski.
;-)))
>1.I think it involves more than proper placement of various body parts;
> it involves very well coordinated muscle movements and precise timing.
> It involves very good balance so the body is not wasting energy
> regaining balance and the muslce movements result in efficient
> propulsion.
> 2. Another thing to think about is how the really good skiers learned
> to ski with the technique you're trying to copy. I can assure you that
> they didn't learn by thinking about physics. I think the good skiers
> learn to ski well by skiing a lot and getting some occasional pointers
> from coaches.
>
1.I emphasis on BALANCE, this is the largest part in good technique, without
good balance there's no way you can compensate for that with other means.
2.Timing is crucial for some of the movement but not as important as balance.
3.Se how other does it, try it and from that develop YOUR OWN STYLE that
works for you.
I just got me a lesson from a guy that is wery good classic skier, the result
on my own technique is intresting, to say the least.
I am in favor of Ken's experiment with the camera, it gives you an outside view
of how you do it. This is wery usefull to correct smaller misstakes and especially
your own perception on how you are doing things, because, you don't do it as you
think
you are doing it.
Mark Drela
> Mark Drela wrote
> > I don't remember seeing anyone separate the
> > power-producing (good) and power-dissipating
> > (bad) muscle action.
>
> I know that I haven't gone that far in my numerical spreadsheet model --
> because it's hard work to generate credible numbers at that level --
> especially for a fully three-dimensional motion like skating, where each
> major body part has six (non-independent) state variables -- subject to
> constraints based on bone-joint geometry, etc.
I think you're making this more complicated than it has to be.
Dissipation by muscles occurs when a muscle is tensed while
being extended in length. Because we have so many muscles,
this is difficult to perceive. Fortunately, there is an
almost equivalent statement in terms of joint motions:
Dissipation by muscles occurs when muscles forces (joint torques
to be exact) are applied opposite to a joint rotation.
For example:
A. In a vertical jump, you apply joint torques at your hip and knee joints
in the same direction as their rotation. The muscles do positive work
which goes into your vertical kinetic energy.
B. In a vertical landing, you apply the same joint torques, but the joints
are now rotating in the opposite direction. The muscles now dissipate
energy.
There is also another dissipative mechanism via impact.
C. In a vertical landing you hold your legs straight and locked (ouch!).
The inelastic impact with the ground dissipates the energy rather
than your muscles.
In skiing, all three types of actions are present. Bad technique
has excessive or unnecessary B and/or C actions which subtract energy
from the positive A actions, leaving less energy for propulsion.
If you can modify your technique so as to reduce B or C actions,
you almost certainly WILL go faster. As I said before, I think this
is the real payoff of better technique. Increased power production
from more vigorous A motions is much less likely, because of the
cardiovascular constraint.
Here are some typical type B skiing actions which should be minimized:
* As the arm comes up and forward to the start of a pole stroke, muscles
reverse its upward motion and force it back down.
It's better to let the arm swing freely and let gravity reverse its motion.
I think fast-turnover V2 poling is inefficient because it seems gravity
can't do this fast enough -- I'm definitely conscious of my muscles
doing some of the motion reversal. Slow-turnover V2 poling seems OK.
* As the arm finishes the pole stroke, muscles reverse its rearward+up
motion, and force it back down and then forward.
Again, better to let gravity reverse the motion.
* Sideways leg motion must involve muscle-driven motion reversals,
since gravity can't help here.
Minimize this by minimizing turnover rate for a given skate angle,
via maximum leg stroke (boots almost touch in the center, toe pointed
at end of stroke).
Here are some type C impact actions which should be minimized:
* Before start of skate stroke, the foot is raised too high and slammed down.
* Poles are slammed down at the start of poling stroke.
The energy put into the leg/ski or arm/pole just heats up the snow
on impact, rather than going into propulsion.
>bicycling is the physically-biomechanically simplest propulsive connection
>between human muscles and the external environment,
Agreed. Pedaling is an example of "forced motion", where the
rapid motion reversals are provided by the cranks and do not
dissipate power -- there isn't too much to pedaling technique
other than pushing at the right points of the pedal circle.
Skiing is "free motion", where reversals do dissipate power,
and technique matters a lot more.
Ken Roberts
right for motions which take place all in the 2-dimensional vertical /
forward-backward plane -- like many poling motions. Or in situations where
there's no simple machine available to convert sideways move into useful
forward work -- like weight-shift in Classic striding.
Mark Drela wrote
> I think you're making this more complicated than it has to be.
But I think the analysis _must_ get more complicated in skating. Because in
skating, some sideways "dissipative" forces can be converted into useful
forward-motion work -- by the magic of the angled ski operating as an
"inclined plane" mechanism.
Therefore we cannot simple count torques or forces typically labeled as
"dissipative" as all wasted. Instead we must determine which _component_ of
the force can be converted into forward-motion work (and with what
efficiency). The big example is sideways torso swing, which generates
useful forward-motion components in _both_ the "eccentric" and the
"concentric" contractions.
The reason is the _de-celeration_ of the mass of a body part also generates
reactive forces by Newton's Third Law -- it's not just acceleration that
does it. And in a complicated fully-three-dimensional motion sequence,
there can arise clever ways to exploit those reactive forces from
de-celeration.
That's just the successful World Cup ski racers do. And they all use the
same basic methods and moves to exploit those
otherwise-typically-"dissipative" forces.
Aspiring racers may choose not to be bothered with learning and refining
those moves. They might succeed to the National level. But they're not
going to make it on the World Cup circuit. You can't compete there if you
start by giving up 2% on simple Newton's-Third-Law physics.
Ken
Mark Drela
> Mark Drela wrote
> > I think you're making this more complicated than it has to be.
>
> But I think the analysis _must_ get more complicated in skating. Because in
> skating, some sideways "dissipative" forces can be converted into useful
> forward-motion work -- by the magic of the angled ski operating as an
> "inclined plane" mechanism. Therefore we cannot simple count torques
> or forces typically labeled as "dissipative" as all wasted.
Not true. Muscle-force torque in the same direction as joint
rotation produces power, and torque opposite to the direction
of joint rotation dissipates power. This principle is the same
for limb motion in any direction.
Joint torques get converted to forces via the bone lever arms
between joints, so talking about forces muddies the picture a bit.
But for illustration or coaching purposes we can talk about
leg extension and "leg force".
The outward skating leg forces do positive propulsive work
if the leg is being extended while you're pushing outward --
that's the usual skating stroke. Dissipation occurs when you
pull inward while the leg is still moving out by inertia.
Here are two possible ways to make the leg reverse direction
and go back inward at the end of the stroke:
A. Push it back by doing a last push by pointing the foot.
B. Pull it back with the upper leg muscles
Method A uses the leg's kinetic energy towards propulsion.
Method B dissipates the leg's kinetic energy.
In actual skating both are surely present, but good technique
maximizes A minimizes B.
Similar options are present in DP. At the end of the pole stroke
you can:
A. Do a sharp final push with the arms to stop the torso's downward movement.
B. Relax the arms and use the back muscles to stop the torso's movement
C. Let the torso slam into the thighs.
Method A does useful propulsive work with the torso's energy,
while B and C dissipate the torso's energy. Good technique
maximizes A and minimizes B and C.
Ken Roberts
skating, but not to all of them.
Mark Drela wrote
> Similar options are present in DP.
I already agreed in a previous post that the Double-Pole push supports the
simplified principle.
> Here are two possible ways to make the leg
> reverse direction and go back inward at the
> end of the stroke
And I now gladly add the recovery of the leg as a supporting example for the
simplified principle.
But I'm still claiming that sideways torso rotation is an important skating
move that does _not_ follow Mark's simplified "dissipative force" principle.
(Not the only one, but the biggest.)
So how about some consideration of that move?
I'll make a very specific claim: During the second phase of his leg-push on
the poling-side ("hang-side") of his V1 skate ("offset", "paddle-dance"),
Carl Swenson starts a move to rotate or "swing" his whole torso toward his
non-poling "off" side. While his torso is in the midst of rotating, he
transfers his body weight to the other ski on his non-poling side, and
starts edging that ski. Then he uses his abdominal muscles to slow and then
stop the torso rotation move.
My claim is this _deceleration_ action generates a reactive force (by "F =
ma") -- and that this reactive force has a partial directional component
vector which is perpendicular to the edge of Carl Swenson's non-poling ski.
I am claiming that this component of the reactive force therefore _adds_ to
the skate-push force thru the non-poling-side ski, and therefore
accomplishes useful forward-motion work, and that helps Carl climb up the
hill faster and/or easier.
Does that make any sense? What are some improvements or corrections to that
analysis?
Ken
todd carter
I was holding this back for a rainy day, but alas, I can no longer
contain myself. The MIT Center for Sports Innovation has done some work
in the area of skate motion analysis that may prove instructive to this
thread
(http://web.mit.edu/afs/athena.mit.edu/dept/aeroastro/www/labs/csi/skating.html).
The idea is that today's athletes expect to use tools to optimise their
performance. That these tools exist in many sports, such as cycling, but
that sophisticated tools are not available to the in-line skater. As a
first step, MIT tried to figure out the qualitative and quantitative
aspects of in-line skating performance.
My suggestion to you, 1) Call MIT. 2) Come up with a research plan &
budget to develop better tools to understand the qualitative and
quantitative aspects of skating ski performance. 3) Build something at
least as cool as an SRM (http://www.srm-usa.com). 4) Sell it on the
Internet to everyone on RSN. 5) Get really rich, retire and ski every day.
See you at the Loppet Jimmy ...
Todd
Nathan Schultz
> Hello all,
snip...
Good work Pete. Some interesting comments with this thread. I
find it somewhat ironic that Pete prefaces his technique ideas with
the USST philosophy on getting the word out and challenging ideas,
rather than challenging individuals, and this is followed by a lot of
sniping back and forth and less and less about the ideas he presented.
We are very lucky to have the USST in its current state, not only
working with the USST athletes, but opening itself and its resources
to elite skiers, and presenting educational information to citizen
racers, nearly all of whom are not even members of the USSA
organization which pays Pete's (woefully inadequate) salary. These
guys are doing this because they love the sport and they are doing
what is best for the sport. If you nit-pick through pages of detailed
descriptions made by anyone, you are going to find seeming
contradictions. Look at the big picture and you should see that he is
describing top-level technique at the elite international level to us.
Focus on minor imprecision in his language, and you can write pages
on technical contradictions in what he says.
A note on the "Physics" analysis of skiing. Certainly, we must
address physics and biomechanics in our technique discussions, and the
physicists out there can offer a tremendous amount in these dialogs.
However, physicists and biomechanicists alike, please be aware that it
is foolish to break skiing technique down into 100% physics or 100%
biomechanics.
I am not saying that natural laws do not apply, but I am saying
that skiing is a horrifically complicated motion, and unless you have
1000 supercomputers running algorithms day and night, figuring out all
of the variations due to terrain, body type, snow conditions, ski
flex, and the myriad other factors that make up the equation of a
skier going down the track, you are not going to be able to understand
skiing, nor will you be able to explain it. There are too many
parameters involved to make a strictly scientific framework.
This fall at a lecture at the CU Engineering department, I had
two experts on physical models of skiing tell me that I push off of my
ski perpendicular to the direction of the ski's travel. I argued that
I was actually pushing more from the side and that one of the most
fundamental errors I see people make in skating is to push "backwards"
or directly perpendicular to the ski. They were so caught up in this
model that they had created, that they could not see that something
could possibly be different than what they had predicted. Even though
they were 100% wrong due to assumptions and simplifications they had
made in order to make their model reasonably simple, they were certain
that I could not possibly be correct because I was describing what I
observed, not what fit into their framework.
That is not to say that science should not be a part of the
discussion. Having physicists evaluating our discussion keeps us
honest and gives us insight. But scientists need to realize that
scientific analysis is only part of the equation, and detailed
scientific analysis may not be required or even desired for every
point in a technique discussion. Sometimes, we need to look at the
bigger picture and talk about imprecise things like ski feel and
"over-rotating".
-Nathan
http://nsavage.com
Andrew Lee
"Nathan Schultz" <nat...@hotmail.com> wrote:
> This fall at a lecture at the CU Engineering department, I had
> two experts on physical models of skiing tell me that I push off of my
> ski perpendicular to the direction of the ski's travel. I argued that
> I was actually pushing more from the side and that one of the most
> fundamental errors I see people make in skating is to push "backwards"
> or directly perpendicular to the ski. They were so caught up in this
> model that they had created, that they could not see that something
> could possibly be different than what they had predicted. Even though
> they were 100% wrong due to assumptions and simplifications they had
> made in order to make their model reasonably simple, they were certain
> that I could not possibly be correct because I was describing what I
> observed, not what fit into their framework.
I think this might be complicated by the difference between what it feels
like we are doing and what we are actually doing. It also depends on our
frame of reference. For instance, if your upper body (and head) are
inclined at a forward angle, from the frame of reference of your body,
kicking directly to the side will have a rearward component when viewed from
a frame of reference outside of your body. I admit that I go for the kick
to the side feeling most of the time and that it's a good teaching tool, but
when I look down, the starting position in the kick of my feet is farther
forward than the ending position relative to my center-of-mass and the
direction of travel. I see this in all the videos too. Some good side
views at Janne's site are PerElof6, Zorsi and Valbusa1. (Valbusa1 shows
both V2 and V1 on the same slope). They look like they are pushing to the
side relative from the frame of reference of their angled bodies, but with a
rearward component from the outside view (look at the sweep of their feet).
If you can point to a clip where you can see the sweep of the feet going
perpendicular to the direction of travel, it would be nice to observe.
I don't think those engineers have it right that they see the kick as
perpendicular to the ski though (from the outside view). It might be at
times, but I think the actual angle varies depending on the technique and
terrain if you look at the hills too. I found this article by Borowski the
other week where he advocates kicking perpendicular to the ski. But I'm not
sure how old the article is or if it's his current thinking.
http://www.sierranordic.com/Tech_tip_six.html .
I was hoping not to get pulled into this thread. Except to say that I like
Pete's ideas and have felt many of his cues learning on my own. Reading his
tips reinforces that I'm on the right track and gives me some more ideas to
use. The progression sequence of "short quick"... to "now your skiing" is
great (somewhat like what I've read of Galanes and other coaches too). But
I was hoping to clarify some of the discussion. As I said, I do like the
"kicking to the side" as a technique tip, but I wanted to point out that
there is a rearward component to it when viewed from the outside (not quite
90 degrees to the side, but not always perpendicular to the ski).
Andrew Lee
Mark Drela
> This fall at a lecture at the CU Engineering department, I had
> two experts on physical models of skiing tell me that I push off of my
> ski perpendicular to the direction of the ski's travel. I argued that
> I was actually pushing more from the side and that one of the most
> fundamental errors I see people make in skating is to push "backwards"
> or directly perpendicular to the ski.
I know I'm going to catch flak for this,
but these "experts" were essentially correct.
One cannot significantly influence the _direction_
of the force that the snow applies to the ski,
only the magnitude. This direction is mostly
perpendicular to the ski base, with a small
rearward tilt due to snow friction. There is
no other physical mechanism to change this.
In turn, the leg force applied to the ski nearly
equal and opposite to the snow force, so the leg
force direction is fixed. Yes, the leg force
is slightly different because the ski and lower leg
are accelerating back and forth, but this difference
is very small. So the bottom line is: The only way
the skier can significantly change the direction
of the leg force is to change the angle of the ski
itself.
The "push sideways" versus "push back"
is a difference in perception, not reality.
I agree that the perception distinction
may be useful in coaching to modify technique.
But also being aware of reality is not
necessarily bad.
Ken Roberts
learn much from reading long _long_ articles that I already agree with.
I did find a drill that looked helpful ("Hot Feet"), and said I would
practice it. And so I did, and it helped (more accurately, it was the
"Nathan Schultz" variation in that post that helped me).
For all the generic reverence expressed for Vordenbergs's post, who else
except Jeff Potter and me actually said they used anything _specific_ from
it? (And who of those generic reverers has actually paid for a copy of
Pete's "Momentum" book and read it through, like I have?)
Nathan Schultz wrote
> Pete prefaces his technique ideas with the USST philosophy
> on getting the word out and challenging ideas . . .
Which were those "challenging" ideas? Most sounded pretty mainstream to me.
When is the USST going to be "getting the word out" on how Carl Swenson
keeps getting such great results while violating a major principle of
Vordenberg's New Skate articles? (How's that for "challenging"?)
> Focus on minor imprecision in his language, and you
> can write pages on technical contradictions in what he says.
No I cannot.
I worked through every sentence of the Skating sections of Vordenberg's
post, and the only thing I could find to question was the _interpretation_
of one drill. (Such an overall assessment could be taken as high praise.)
The "old Pete" was more fun.
Ken
phof...@math.uwaterloo.ca
Pete's article (which I appreciated very much without having chimed
in earlier, though I should be doubly grateful, since none of my
tax $CAN go to pay his salary!). My lack of symmetry in V1 leg action,
"bogging down on the non-poling side" as he puts it, has been pretty obvious to
me, so I've been taking his advice about skating off with the knee
pushed down and forward, and consciously trying to avoid standing up.
This Saturday's skate race is o the home course of Al Pilcher, a guy
who had some very good results in the Pierre Harvey era for the canadian
team. It's just never-ending ups and downs, mostly too steep for more
than one or two strokes of V2 (sorry, 1-skate, after all we're in
Orangeville, Canada!), so lots of offset. But you guys at Lake Placid
have to ski 5 times farther, a different, but not necessarily worse,
kind of pain. We get to do a classic race Sunday on the same course.
So I'll take his advice about not over-striding, though I'm not
sure that has been one of my classic sins.
Best, Peter phof...@math.uwaterloo.ca
Ken Roberts
sharing it, Todd.
http://web.mit.edu/afs/athena.mit.edu/dept/aeroastro/www/labs/csi/skating.html
Looks like they've attached a good range of sensors to the skates -- and
also captured and integrated the measurements in a helpful way. It's not
precisely about skiing, but I love inline skates too, so you guessed
right -- I'll be giving them a call. It would be fun to try to get them
working on questions that could result in more specific analysis than their
first experiment (and contrary to their humble assessment, I would be _glad_
for 0.4% accuracy in sensor readings of skating).
I liked the direction of their second experiment on vibration: It would be
great to see some new mechanical approach to making road skating over rough
surfaces more fun.
I think the _technology_ for applying this to XC skis is straightforward.
(I met some mechanical engineers at U of Utah who could have done much of it
ten years ago. Except that they were backcountry skiers -- I had no
interest in XC back then, and no idea there were big-time National-team XC
racers hanging there in Salt Lake.) With the oil money available to the
Norwegian team, I'd be surprised if they haven't already constructed a ski
with force sensors under the binding.
Real-time force-sensor-analysis to help racers find weak spots in their
stroke cycles could become the next "unfair" advantage in World Cup racing.
(Actually I'd guess the bigger paybacks are from time-series analysis of
fore-center-aft foot-pressure distributions thru the stroke cycle of
_Classic_ striding, because of the trickiness of getting both grip and glide
thru the same ski).
> 3) Build something at least as cool as an SRM.
> 4) Sell it on the Internet to everyone on RSN.
Good idea -- but I think I'll wait first to see the blockbuster sales
results from Nathan's video and book.
Ken
phof...@math.uwaterloo.ca
at the same time not considering it likely that absorbing it will
make me a faster skier. So I ask the following just as a matter of
intellectual interest. (End of disclaimer for those who get impatient
with this kind of thing.)
The question relates to Mark Drela's post concerning the push by the
leg, saying that it can't in reality be sideways if the ski is angled
quite a bit, but must be close in direction to perpendicular to the
length of the ski. Probably it comes down to the definition of the
word "push", some kind of operational definition, rather than mathematical
definition. Imagine an astronaut floating in space on a nice long tether,
whose space suit ends on each leg in a Pilot boot attached to his
indifferently waxed RCS's. So there's no snow to push against, and no
track direction, but his center of mass and body give a perfectly good
reference frame for the following to be meaningful. The skis are
at angle 45deg to the direction he is facing. First he swings his leg
straight out to the side. Next time he swings his leg to the side and
backwards so that it's perpendicular to the ski. I've been assuming
that what the coaches are saying is that he should be spending his
time doing the first, not the second, if it's a bit of training for
his next ski race in the polar regions of Mars that he's training for.
Everything I just said sounds very tediously obvious to me, but maybe
nedds correction. The real queston is to explain why the first rather
than the second makes you have better race results.
Best, Peter phof...@math.uwaterloo.ca
bm...@deletethis.d.umn.edu
Drela wrote:
> In article <8633c0ba.04012...@posting.google.com>,
nat...@hotmail.com (Nathan Schultz) writes:
> >> This fall at a lecture at the CU Engineering department, I had
>> two experts on physical models of skiing tell me that I push off of my
>> ski perpendicular to the direction of the ski's travel. I argued that
>> I was actually pushing more from the side and that one of the most
>> fundamental errors I see people make in skating is to push "backwards"
>> or directly perpendicular to the ski.
>
> I know I'm going to catch flak for this,
> but these "experts" were essentially correct.
That's what I was thinking too. Assuming you have perfect wax (i.e.,
no friction), the only force the snow exerts on the ski is
perpendicular to the ski (i.e., because it's on edge). Thus,
considering the person/ski as a single body, the only force on the
person/ski is perpendicular to the ski, so the only force that the
person/ski can exert on the snow is also perpendicular to the ski
(Newton's 3rd Law). Interpretation: Pushing perpendicular to
the ski can accelerate you and get you somewhere. Pushing along the
ski simply moves the ski forward or backward relative to the person
(i.e., rotation about the person/ski center of mass).
That last point is very important however. How the person pushes off
the ski (i.e., whether their foot is forward or backward) determines
their body postion and how well they will be balanced when they land
on the other ski, etc., etc. This is the sort of thing that coaches
should focus on.
Cheers,
Brian
Mark Drela
> Imagine an astronaut floating in space on a nice long tether,
> First he swings his leg straight out to the side.
> Next time he swings his leg to the side and
> backwards so that it's perpendicular to the ski.
> The real queston is to explain why the first rather
> than the second makes you have better race results.
This scenario is not relevant to skiing, because
the astronaut is not applying significant forces
to move his feet in the ways you describe.
I was talking about the direction of the leg force
applied to the ski, not the direction of the
ski movement.