suggestions for my technique on video

On Fri, 26 Jan 2007 01:05:34 GMT, "Ken Roberts"
wrote:

John Forrest Tomlinson wrote
There are certain fundamentals that are applicable
to a lot of sports that take place on two feet.

Yes there are lots of things that are shared, but there is one key thing in
the physics that makes skating different from other muscle-powered
propulsive motions like running, seated bicycling, and classic skiing:
The ski (or ice or inline skate) while gliding can transform the _direction_
of physical Force and Work in a special way -- by acting as a "simple
machine" called an "inclined plane".

In particular the ski (or inline or ice skate) can transform sideways-aimed
Force and Work into backward-aimed Force and Work. Because of this special
physics there are opportunities in skating for using sideways muscle moves
to add to forward motion Work and Power -- in ways that are not possible
with most other human-muscle-powered propulsive methods.

So it can be possible that sideways motions which are counter-productive in
other sports can be helpful in propulsion by skating.

I'm not talking about just rotation -- I'm talking about basic,
athletic body posture and leading with the core, not leading with head
motions.
--
JT
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Yes, the actual studies and methodolgy would be helpful, hopefully
done by established researchers as opposed to xczone studying video.
KNT is inefficient biomechanics, and really a bogeyman that's being
still carried on by people who should know better; good skiers always
turn less than the angle of the ski. The position xczone was presumably
defending was that top skiers don't turn very much - they'd like to
say not at all ("facing down the track"). Since skiers are constantly
rotating the torso, the claim of approx. zero degree rotation for most
of the cycle misses the point and, watching for example a nearly
straight-on video such as Kuusamo, it doesn't even appear to be true. I
did get your point about the max of 60 degrees, but did you get
mine: what is the distribution of those turns, and what is the
distribution of the proportions of turn to skate direction? I'll bet
the former are weighted toward the 45-60 degree end in V1, and the
latter are not trivial in any technique. I am not sure what the 0.3
seconds refers to, or perhaps of what significance it is, because a
study(s) of V1 have shown it takes ~0.75 seconds from strong side pole
plant to maximum force (a bit longer from the weak side pole plant,
which for many top skiers came and perhaps still comes first). But like
you say, we need the studies to evaluate the claims.

rm


wrote:

Just so it is clear, the DVD is talking about V1 / steep hills and 60
degree rotation max _observed_. Flatter terrain results in much smaller
angles (IE 5 degrees over flats). In addition, the rotation only lasts
for 0.3 seconds (extremely short period of time given the complete
skate motion). So it is a terrain specific case + they are clear there
is a length of time that must be considered. Don't think they are
contradicting themselves, just indicating different terrain will
require different techniques.

These degree statistics are from a sports study of Top 20 XC skiers
over 5 years (empirical data from top result winners). Would be nice to
have a reference to the actual studies as well.

On Jan 25, 1:44 pm, wrote:
100 degrees, definitely not. The Austrian skate video, Perfect
Skating, says that next skate ski goes at a right angle to the
previous one. Try it. That's a lot, and more than you'll see or need
in any technique. 70-80 degrees seems to be about tops I see or have
experienced. Which means that no matter which of the figures you
choose, 60 degrees is effectively turning in the direction of the
ski, without fully aligning KNT. Normally, there's neither time nor
need to do so. Looking at videos, good skaters who didn't get caught
up in the American KNT craze having been doing it that way since the
1980s. I don't know where the XC Zone is today, but my understanding
from reading the polemics is that they were "New Skate" proponents,
denying any turn at all. Thus, admitting 60 degrees would be
tantamount to capitulation, whether they realize it or not.

wrote:
Sorry if this gets posted twice.

A great DVD on this topic would be to check out:

http://www.xczone.com/newskitech.htm

There is a section that talks specifically about body rotation as
part of weight transfer. Many folks learn early on an exaggerated
weight transfer involving aligning nose / knee / toes on each
skate. There is a segment on this topic at ~ 54-60 minutes in.

At ~62-65 minutes, there is more of a scientific discussion of how
much rotation the Top 20 XC skiers exhibited in a variety of
terrain over a 5 year analysis period. Assume nose/knee/toe
rotation is 100 degrees. Top skiers rotate less than 60 degrees max
on steep hills. On relatively flat terrain, this drops to 5 degrees
max. Sprint finishes are close to 1-2 degrees max (assume it was
based on flat terrain sprints). So there is some rotation but not a
huge amount. The DVD also points to research that shows these
rotations are only for 0.3 of a second and the remainder of the
glide is pretty much zero degree rotation. So whatever rotation
there is, it is not for long.

The DVD does not indicate if top 20 skiers exhibit more rotation
than the top skiers. But I think the emphasis is clear, excessive
rotation interferes with forward motion (in general). Top skiers
studied exhibit a relatively small amount of rotation even over
difficult terrain.

I think the methodology is fairly well discussed in the DVD without
killing the flow of the presentation. I don't think xczone is in the
business of publishing dry academic papers. The volume of published
products (more than any other entity that I can find), competition
results, coaching and academic credentials strongly qualifies xczone as
established researchers and practicioners. There are a number of
references to IOC medical journals and field testing in the DVD. I am
not sure that I agree with all what the IOC sports medicine 'experts'
said. The problem with many "academics" studying skiing in the lab is
that they don't ski.

Here, with xczone, we have a pragmatic approach by elite skiers who
have degrees in exercise physiology and biomechnical engineering.

Without getting caught-up in degrees, what I took away from the Nordic
Skiing Technique DVD is that there are no absolutes but generally most
people twist too much, and racers tend towards a progressive or new
skate, whereas beginners use older skate (KNT) to get around and shift
weight.

If I had to guess, the message in the xczone dvd is closer to the USSA
which very much pushing new skate (no rotation) and Cross Country
Canada's doctrine than it is Old Skate (KNT), but they have left a bit
of room for debate.

Thoughts?

DH


On Jan 25, 9:35 pm, wrote:
Yes, the actual studies and methodolgy would be helpful, hopefully
done by established researchers as opposed toxczonestudying video.
KNT is inefficient biomechanics, and really a bogeyman that's being
still carried on by people who should know better; good skiers always
turn less than the angle of the ski. The positionxczonewas presumably
defending was that top skiers don't turn very much - they'd like to
say not at all ("facing down the track"). Since skiers are constantly
rotating the torso, the claim of approx. zero degree rotation for most
of the cycle misses the point and, watching for example a nearly
straight-on video such as Kuusamo, it doesn't even appear to be true. I
did get your point about the max of 60 degrees, but did you get
mine: what is the distribution of those turns, and what is the
distribution of the proportions of turn to skate direction? I'll bet
the former are weighted toward the 45-60 degree end in V1, and the
latter are not trivial in any technique. I am not sure what the 0.3
seconds refers to, or perhaps of what significance it is, because a
study(s) of V1 have shown it takes ~0.75 seconds from strong side pole
plant to maximum force (a bit longer from the weak side pole plant,
which for many top skiers came and perhaps still comes first). But like
you say, we need the studies to evaluate the claims.

rm



wrote:
Just so it is clear, the DVD is talking about V1 / steep hills and 60
degree rotation max _observed_. Flatter terrain results in much smaller
angles (IE 5 degrees over flats). In addition, the rotation only lasts
for 0.3 seconds (extremely short period of time given the complete
skate motion). So it is a terrain specific case + they are clear there
is a length of time that must be considered. Don't think they are
contradicting themselves, just indicating different terrain will
require different techniques.

These degree statistics are from a sports study of Top 20 XC skiers
over 5 years (empirical data from top result winners). Would be nice to
have a reference to the actual studies as well.

On Jan 25, 1:44 pm, wrote:
100 degrees, definitely not. The Austrian skate video, Perfect
Skating, says that next skate ski goes at a right angle to the
previous one. Try it. That's a lot, and more than you'll see or need
in any technique. 70-80 degrees seems to be about tops I see or have
experienced. Which means that no matter which of the figures you
choose, 60 degrees is effectively turning in the direction of the
ski, without fully aligning KNT. Normally, there's neither time nor
need to do so. Looking at videos, good skaters who didn't get caught
up in the American KNT craze having been doing it that way since the
1980s. I don't know where the XC Zone is today, but my understanding
from reading the polemics is that they were "New Skate" proponents,
denying any turn at all. Thus, admitting 60 degrees would be
tantamount to capitulation, whether they realize it or not.

wrote:
Sorry if this gets posted twice.

A great DVD on this topic would be to check out:

http://www.xczone.com/newskitech.htm

There is a section that talks specifically about body rotation as
part of weight transfer. Many folks learn early on an exaggerated
weight transfer involving aligning nose / knee / toes on each
skate. There is a segment on this topic at ~ 54-60 minutes in.

At ~62-65 minutes, there is more of a scientific discussion of how
much rotation the Top 20 XC skiers exhibited in a variety of
terrain over a 5 year analysis period. Assume nose/knee/toe
rotation is 100 degrees. Top skiers rotate less than 60 degrees max
on steep hills. On relatively flat terrain, this drops to 5 degrees
max. Sprint finishes are close to 1-2 degrees max (assume it was
based on flat terrain sprints). So there is some rotation but not a
huge amount. The DVD also points to research that shows these
rotations are only for 0.3 of a second and the remainder of the
glide is pretty much zero degree rotation. So whatever rotation
there is, it is not for long.

The DVD does not indicate if top 20 skiers exhibit more rotation
than the top skiers. But I think the emphasis is clear, excessive
rotation interferes with forward motion (in general). Top skiers
studied exhibit a relatively small amount of rotation even over
difficult terrain.- Hide quoted text -- Show quoted text -

On the Austrian skate CD, the World Cup Skiers rotated very little, but
when they had their own skiers demonstrate skating techniques they had
significantly more twist and KNT - it seemed contrary.

After listening again to the xczone DVD, the max 60 degrees rotation
referred to was only noticable for a brief moment on the steepest
climbs and then the skiers position "quickly moderated towards center."


The KNT approach in the Austrian Perfect Skating CD has their skiers
prolonging a full 90 degrees twist on even easy terrain.

That is my take on the two approaches...

DH

On Jan 25, 4:44 pm, wrote:
100 degrees, definitely not. The Austrian skate video, Perfect
Skating, says that next skate ski goes at a right angle to the previous
one. Try it. That's a lot, and more than you'll see or need in any
technique. 70-80 degrees seems to be about tops I see or have
experienced. Which means that no matter which of the figures you
choose, 60 degrees is effectively turning in the direction of the ski,
without fully aligning KNT. Normally, there's neither time nor need to
do so. Looking at videos, good skaters who didn't get caught up in the
American KNT craze having been doing it that way since the 1980s. I
don't know where the XC Zone is today, but my understanding from
reading the polemics is that they were "New Skate" proponents, denying
any turn at all. Thus, admitting 60 degrees would be tantamount to
capitulation, whether they realize it or not.

rm



wrote:
Sorry if this gets posted twice.

A great DVD on this topic would be to check out:

http://www.xczone.com/newskitech.htm

There is a section that talks specifically about body rotation as part
of weight transfer. Many folks learn early on an exaggerated weight
transfer involving aligning nose / knee / toes on each skate. There is
a segment on this topic at ~ 54-60 minutes in.

At ~62-65 minutes, there is more of a scientific discussion of how much
rotation the Top 20 XC skiers exhibited in a variety of terrain over a
5 year analysis period. Assume nose/knee/toe rotation is 100 degrees.
Top skiers rotate less than 60 degrees max on steep hills. On
relatively flat terrain, this drops to 5 degrees max. Sprint finishes
are close to 1-2 degrees max (assume it was based on flat terrain
sprints). So there is some rotation but not a huge amount. The DVD also
points to research that shows these rotations are only for 0.3 of a
second and the remainder of the glide is pretty much zero degree
rotation. So whatever rotation there is, it is not for long.

The DVD does not indicate if top 20 skiers exhibit more rotation than
the top skiers. But I think the emphasis is clear, excessive rotation
interferes with forward motion (in general). Top skiers studied exhibit
a relatively small amount of rotation even over difficult terrain.- Hide quoted text -- Show quoted text -

Thanks, Darlene, for a perfect example of the type of argument the
New Skate proponents engaged in for several years: poo-pooing the
understanding of biomechanics, seat-of-pants video analysis by coaches
and competitors as "established research," and dismissal as "dry
academic papers" of the work done by world-class sports scientists
attached to the leading sports and ski research centers in Scandanavia
countries (and the world). It's telling that the New Skate ideas, as
well as the earlier pushing of KNT, were North American products, really
U.S. I think, and the discussion died with the lack of results (try
finding a video of Becky Scott doing either in V1). This is not to
suggest that there haven't been shifts over time in both skate and
classical techniques, most coming as a result of improved training,
equipment and competition levels (and, in Germany, some different ideas
about body position, movement and efficiency).

The two questions I raised about the distribution of torso and
head rotation in different techniques and terrain, and the distribution
of % of upper body turn relative to ski angle are empirical questions
that would be part of a good systematic description and analysis of
what skiers actually do. The Austrian skate CD came to mind as a
visual reference point because they talk about one ski moving at a
"right angle" to the other, although I suspect they mean that
figuratively rather than literally. The New Skate proponents argued
against KNT primarily with regard to V1 technique, which is where it
had been focused on in the U.S. The Austrian CD raises it *only in the
context of the V2 techniques. For example (and this is just one slide
of a sequence from the cycle):

"At the end of the push off, the weight is completely transferred to
the new gliding ski.
- Your nose, knee, hip and ankle are vertically aligned over the
gliding ski.
- Glide on a flat ski to achieve a stable and steady glide.
- Stabilize your hip and shoulder and keep them parallel to each
other."

Sounds good to me.

rm



wrote:

I think the methodology is fairly well discussed in the DVD without
killing the flow of the presentation. I don't think xczone is in the
business of publishing dry academic papers. The volume of published
products (more than any other entity that I can find), competition
results, coaching and academic credentials strongly qualifies xczone as
established researchers and practicioners. There are a number of
references to IOC medical journals and field testing in the DVD. I am
not sure that I agree with all what the IOC sports medicine 'experts'
said. The problem with many "academics" studying skiing in the lab is
that they don't ski.

Here, with xczone, we have a pragmatic approach by elite skiers who
have degrees in exercise physiology and biomechnical engineering.

Without getting caught-up in degrees, what I took away from the Nordic
Skiing Technique DVD is that there are no absolutes but generally most
people twist too much, and racers tend towards a progressive or new
skate, whereas beginners use older skate (KNT) to get around and shift
weight.

If I had to guess, the message in the xczone dvd is closer to the USSA
which very much pushing new skate (no rotation) and Cross Country
Canada's doctrine than it is Old Skate (KNT), but they have left a bit
of room for debate.

Thoughts?

DH


On Jan 25, 9:35 pm, wrote:
Yes, the actual studies and methodolgy would be helpful, hopefully
done by established researchers as opposed toxczonestudying video.
KNT is inefficient biomechanics, and really a bogeyman that's being
still carried on by people who should know better; good skiers always
turn less than the angle of the ski. The positionxczonewas presumably
defending was that top skiers don't turn very much - they'd like to
say not at all ("facing down the track"). Since skiers are constantly
rotating the torso, the claim of approx. zero degree rotation for
most of the cycle misses the point and, watching for example a nearly
straight-on video such as Kuusamo, it doesn't even appear to be
true. I did get your point about the max of 60 degrees, but did you
get mine: what is the distribution of those turns, and what is the
distribution of the proportions of turn to skate direction? I'll bet
the former are weighted toward the 45-60 degree end in V1, and the
latter are not trivial in any technique. I am not sure what the 0.3
seconds refers to, or perhaps of what significance it is, because a
study(s) of V1 have shown it takes ~0.75 seconds from strong side
pole plant to maximum force (a bit longer from the weak side pole
plant, which for many top skiers came and perhaps still comes
first). But like you say, we need the studies to evaluate the
claims.

rm



wrote:
Just so it is clear, the DVD is talking about V1 / steep hills and
60 degree rotation max _observed_. Flatter terrain results in much
smaller angles (IE 5 degrees over flats). In addition, the rotation
only lasts for 0.3 seconds (extremely short period of time given
the complete skate motion). So it is a terrain specific case + they
are clear there is a length of time that must be considered. Don't
think they are contradicting themselves, just indicating different
terrain will require different techniques.

These degree statistics are from a sports study of Top 20 XC skiers
over 5 years (empirical data from top result winners). Would be
nice to have a reference to the actual studies as well.

On Jan 25, 1:44 pm, wrote:
100 degrees, definitely not. The Austrian skate video, Perfect
Skating, says that next skate ski goes at a right angle to the
previous one. Try it. That's a lot, and more than you'll see or
need in any technique. 70-80 degrees seems to be about tops I see
or have experienced. Which means that no matter which of the
figures you choose, 60 degrees is effectively turning in the
direction of the ski, without fully aligning KNT. Normally,
there's neither time nor need to do so. Looking at videos, good
skaters who didn't get caught up in the American KNT craze having
been doing it that way since the 1980s. I don't know where the XC
Zone is today, but my understanding from reading the polemics is
that they were "New Skate" proponents, denying any turn at all.
Thus, admitting 60 degrees would be tantamount to capitulation,
whether they realize it or not.

wrote:
Sorry if this gets posted twice.

A great DVD on this topic would be to check out:

http://www.xczone.com/newskitech.htm

There is a section that talks specifically about body rotation as
part of weight transfer. Many folks learn early on an exaggerated
weight transfer involving aligning nose / knee / toes on each
skate. There is a segment on this topic at ~ 54-60 minutes in.

At ~62-65 minutes, there is more of a scientific discussion of
how much rotation the Top 20 XC skiers exhibited in a variety of
terrain over a 5 year analysis period. Assume nose/knee/toe
rotation is 100 degrees. Top skiers rotate less than 60 degrees
max on steep hills. On relatively flat terrain, this drops to 5
degrees max. Sprint finishes are close to 1-2 degrees max
(assume it was based on flat terrain sprints). So there is some
rotation but not a huge amount. The DVD also points to research
that shows these rotations are only for 0.3 of a second and the
remainder of the glide is pretty much zero degree rotation. So
whatever rotation there is, it is not for long.

The DVD does not indicate if top 20 skiers exhibit more
rotation than the top skiers. But I think the emphasis is clear,
excessive rotation interferes with forward motion (in general).
Top skiers studied exhibit a relatively small amount of rotation
even over difficult terrain.- Hide quoted text -- Show quoted
text -

There are some mistakes you need a Phd to make... One "world-class"
sports scientist
attached to a leading sports and ski research center (the IOC Sports
Medicince Council) said that "skiers appear to not use the abdominals
in double poling uphill" because they did not observe much motion.

Of course, any skier who has ever tried to double pole up hill, knows
it can be an ab burner.

Too often coaches and scientists paint themselves into a corner with
absolute statements of what is right, both presenting their arguments
vicariously through video footage of athletes they have never met. The
thing I liked about both Pete Vordenberg and the xczone crew is that
they actually demo their approach personnally. So a viewer can either
take it or leave it.

I think we need a mix of objective sports science and practical insight
of a racer, to approach the truth.
DH

On Jan 26, 3:08 pm, wrote:
Thanks, Darlene, for a perfect example of the type of argument the
New Skate proponents engaged in for several years: poo-pooing the
understanding of biomechanics, seat-of-pants video analysis by coaches
and competitors as "established research," and dismissal as "dry
academic papers" of the work done by world-class sports scientists
attached to the leading sports and ski research centers in Scandanavia
countries (and the world). It's telling that the New Skate ideas, as
well as the earlier pushing of KNT, were North American products, really
U.S. I think, and the discussion died with the lack of results (try
finding a video of Becky Scott doing either in V1). This is not to
suggest that there haven't been shifts over time in both skate and
classical techniques, most coming as a result of improved training,
equipment and competition levels (and, in Germany, some different ideas
about body position, movement and efficiency).

The two questions I raised about the distribution of torso and
head rotation in different techniques and terrain, and the distribution
of % of upper body turn relative to ski angle are empirical questions
that would be part of a good systematic description and analysis of
what skiers actually do. The Austrian skate CD came to mind as a
visual reference point because they talk about one ski moving at a
"right angle" to the other, although I suspect they mean that
figuratively rather than literally. The New Skate proponents argued
against KNT primarily with regard to V1 technique, which is where it
had been focused on in the U.S. The Austrian CD raises it *only in the
context of the V2 techniques. For example (and this is just one slide
of a sequence from the cycle):

"At the end of the push off, the weight is completely transferred to
the new gliding ski.
- Your nose, knee, hip and ankle are vertically aligned over the
gliding ski.
- Glide on a flat ski to achieve a stable and steady glide.
- Stabilize your hip and shoulder and keep them parallel to each
other."

Sounds good to me.

rm

wrote:
I think the methodology is fairly well discussed in the DVD without
killing the flow of the presentation. I don't thinkxczoneis in the
business of publishing dry academic papers. The volume of published
products (more than any other entity that I can find), competition
results, coaching and academic credentials strongly qualifiesxczoneas
established researchers and practicioners. There are a number of
references to IOC medical journals and field testing in the DVD. I am
not sure that I agree with all what the IOC sports medicine 'experts'
said. The problem with many "academics" studying skiing in the lab is
that they don't ski.

Here, withxczone, we have a pragmatic approach by elite skiers who
have degrees in exercise physiology and biomechnical engineering.

Without getting caught-up in degrees, what I took away from the Nordic
Skiing Technique DVD is that there are no absolutes but generally most
people twist too much, and racers tend towards a progressive or new
skate, whereas beginners use older skate (KNT) to get around and shift
weight.

If I had to guess, the message in thexczonedvd is closer to the USSA
which very much pushing new skate (no rotation) and Cross Country
Canada's doctrine than it is Old Skate (KNT), but they have left a bit
of room for debate.

Thoughts?

DH

On Jan 25, 9:35 pm, wrote:
Yes, the actual studies and methodolgy would be helpful, hopefully
done by established researchers as opposed toxczonestudying video.
KNT is inefficient biomechanics, and really a bogeyman that's being
still carried on by people who should know better; good skiers always
turn less than the angle of the ski. The positionxczonewas presumably
defending was that top skiers don't turn very much - they'd like to
say not at all ("facing down the track"). Since skiers are constantly
rotating the torso, the claim of approx. zero degree rotation for
most of the cycle misses the point and, watching for example a nearly
straight-on video such as Kuusamo, it doesn't even appear to be
true. I did get your point about the max of 60 degrees, but did you
get mine: what is the distribution of those turns, and what is the
distribution of the proportions of turn to skate direction? I'll bet
the former are weighted toward the 45-60 degree end in V1, and the
latter are not trivial in any technique. I am not sure what the 0.3
seconds refers to, or perhaps of what significance it is, because a
study(s) of V1 have shown it takes ~0.75 seconds from strong side
pole plant to maximum force (a bit longer from the weak side pole
plant, which for many top skiers came and perhaps still comes
first). But like you say, we need the studies to evaluate the
claims.

rm

wrote:
Just so it is clear, the DVD is talking about V1 / steep hills and
60 degree rotation max _observed_. Flatter terrain results in much
smaller angles (IE 5 degrees over flats). In addition, the rotation
only lasts for 0.3 seconds (extremely short period of time given
the complete skate motion). So it is a terrain specific case + they
are clear there is a length of time that must be considered. Don't
think they are contradicting themselves, just indicating different
terrain will require different techniques.

These degree statistics are from a sports study of Top 20 XC skiers
over 5 years (empirical data from top result winners). Would be
nice to have a reference to the actual studies as well.

On Jan 25, 1:44 pm, wrote:
100 degrees, definitely not. The Austrian skate video, Perfect
Skating, says that next skate ski goes at a right angle to the
previous one. Try it. That's a lot, and more than you'll see or
need in any technique. 70-80 degrees seems to be about tops I see
or have experienced. Which means that no matter which of the
figures you choose, 60 degrees is effectively turning in the
direction of the ski, without fully aligning KNT. Normally,
there's neither time nor need to do so. Looking at videos, good
skaters who didn't get caught up in the American KNT craze having
been doing it that way since the 1980s. I don't know where the XC
Zone is today, but my understanding from reading the polemics is
that they were "New Skate" proponents, denying any turn at all.
Thus, admitting 60 degrees would be tantamount to capitulation,
whether they realize it or not.

wrote:
Sorry if this gets posted twice.

A great DVD on this topic would be to check out:

http://www.xczone.com/newskitech.htm

There is a section that talks specifically about body rotation as
part of weight transfer. Many folks learn early on an exaggerated
weight transfer involving aligning nose / knee / toes on each
skate. There is a segment on this topic at ~ 54-60 minutes in.

At ~62-65 minutes, there is more of a scientific discussion of
how much rotation the Top 20 XC skiers exhibited in a variety of
terrain over a 5 year analysis period. Assume nose/knee/toe
rotation is 100 degrees. Top skiers rotate less than 60 degrees
max on steep hills. On relatively flat terrain, this drops to 5
degrees max. Sprint finishes are close to 1-2 degrees max
(assume it was based on flat terrain sprints). So there is some
rotation but not a huge amount. The DVD also points to research
that shows these rotations are only for 0.3 of a second and the
remainder of the glide is pretty much zero degree rotation. So
whatever rotation there is, it is not for long.

The DVD does not indicate if top 20 skiers exhibit more
rotation than the top skiers. But I think the emphasis is clear,
excessive rotation interferes with forward motion (in general).
Top skiers studied exhibit a relatively small amount of rotation
even over difficult terrain.- Hide quoted text -- Show quoted
text -

How about tennis, which certainly involves application of
substantial sideways force? Here's something in Saturday's NY Times
from the coach of Fernando Gonzalez (playing Roger Federer in the
Australian Open final):

“When I started working with Fernando, I asked him, ‘Why do you play
like that?’ � Stefanki said, referring to his tendency to go for broke
with his ground strokes. “He told me that he just knew if the rally
went on for long, he’d miss on the backhand side.�

One of Stefanki’s techniques is to improve his players’ upper-body
control so they improve their margin for error as they move toward
contact. “Roger is a good example, because he moves with the lower
body, but his upper body is still on both sides,� Stefanki said.

rm

"Ken Roberts" wrote:

John Forrest Tomlinson wrote
There are certain fundamentals that are applicable
to a lot of sports that take place on two feet.

Yes there are lots of things that are shared, but there is one key
thing in the physics that makes skating different from other
muscle-powered propulsive motions like running, seated bicycling, and
classic skiing: The ski (or ice or inline skate) while gliding can
transform the _direction_ of physical Force and Work in a special way
-- by acting as a "simple machine" called an "inclined plane".

In particular the ski (or inline or ice skate) can transform
sideways-aimed Force and Work into backward-aimed Force and Work.
Because of this special physics there are opportunities in skating for
using sideways muscle moves to add to forward motion Work and Power --
in ways that are not possible with most other human-muscle-powered
propulsive methods.

So it can be possible that sideways motions which are
counter-productive in other sports can be helpful in propulsion by
skating.

Ken

rm wrote
How about tennis, which certainly involves
application of substantial sideways force?

A tennis player often uses substantial sideways force -- in order to move
the player's body sideways. Not forward. In order to move forward, the
tennis player pushes her or his foot backward against the court surface.

The magical physics of skating on skis and ice blades and inline + rollerski
wheels can "automatically" convert leg-push sideways force into a backward
force against the ground. Tennis shoes don't do anything like that.

Ken

John Forrest Tomlinson wrote
I'm talking about basic, athletic body posture and
leading with the core, not leading with head motions.

I think the concept of initiating motion from the hips and lower abdoment
while delaying the other parts does not apply to most head motions.

I agree that it's advantageous for propulsive power to initiate pushing
moves from the core and activate muscles roughly sequentially (with lots of
overlap) outward to the hands for poling, or sequentially down to the feet
for leg-push. This is because the muscles further out have two roles: (a)
adding propulsive work motion of their own; and (b) transmitting propulsive
work from other muscles which are not directly connected to the pole or the
ski. Since the muscles further out are usually smaller, they cannot
effectively perform both roles simultaneously, so instead they perform them
in sequence: first (b) holding stable and transmitting work from the
(usually bigger) muscles closer to the core, then second after those bigger
muscles are mostly finished with their work motion, comes role (a) adding
some work motion of their own.

What about the head? While the head is far from the body core, it is not
_transmitting_ any work to anything (except for heading the ball in football
/ soccer, or perhaps helmet-spearing the ball-carrier in American-style
football). So while there's good sound physics to justify initiating the
double-pole push from the hips and abdomnen while delaying the arms and
hands -- and good sound physics to justify initiating Classic or Skating
leg-push from the hips while delaying the ankles . . . There's nothing but
old coaching lore to justify delaying a head-move.

Actually if anything the physics suggests that initiating a ducking of the
head _early_ might be advantageous for power, to add some kinetic energy to
the pole-push when the tips hit the ground later. (Ducking the head too much
later might even reduce the power of poling.) So in physics the neck and
head play a role in poling similar to a "core" muscle, even if in some old
coaching lore they're designated as peripheral to be delayed.

While there may be some World Cup racers (e.g. Kris Freeman) who avoid
ducking their head early, I've analyzed other videos that show famous World
Cup winners starting a "ducking" move of their head forward and down exactly
simultaneous with (or possibly an instant sooner than?) any forward move of
the torso from the lower abdomen or hips -- and this ducking move of their
head is quicker than the lower core move, and soon gets a bit ahead of their
lower "core" motion. Certainly this ducking of the head comes way before the
pole tips ever hit the ground.

I am not here advocating "leading with the head" for XC skiing. Based on
this analysis of the physics, I am advocating not _worrying_ much about head
motions while XC skiing -- as long as you can look where you're going often
enough.

Ken

DH wrote
The problem with many "academics" studying skiing
in the lab is that they don't ski.

How do you know that?
There's no significant reward in doing research on cross-country skiing. I
greatly doubt there are many people doing much significant research on it
unless have some love for getting out and skiing (or at least did when they
were younger).

with xczone, we have a pragmatic approach by elite
skiers who have degrees in exercise physiology and
biomechnical engineering.

Taking some courses and getting a degree in a field is usually very
different from doing real scientific research.

The recent xczone.tv videos indeed have lots of good "pragmatic" tips about
how to ski, and good video segments of skiers demonstrating good techniques.
I think I'm remembering that the one I liked best was where they worked
closely with CANSI, I think called "Ski Your Best".

The "science" video of theirs which I saw gets into more _detailed_ talking
about technique than I've seen in other videos, and much of it I agree with
and some I don't. But more detail is not the same same thing as serious
science. (and "spinning" the numerical results to favor one side of an old
controversy is a very long way from serious science).

Now I only saw the "science" video; did not get to look at the non-video
info that's supposed to be on one of the xczone DVDs, so possibly there's
some serious science there -- with like testable quantifiable models that
tie to established concepts of real physics and engineering, like work
measured in Newtons, power measured in Watts (instead of old coaching lore
words like "loading the ski").

Ken