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Skate technique USST two cents



 
 
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  #21  
Old January 15th 04, 11:43 PM
Jay Tegeder
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Default Skate technique USST two cents

I could care less about technique because I'm not a coach and I just
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 ****ed 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

wrote in message ...
Pete, thanks for the great post. And, congrats on the excellent
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 , Roger
Knight wrote:
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!

Ads
  #22  
Old January 16th 04, 12:34 AM
Mark Drela
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Default Skate technique USST two cents

In article , "Griss" writes:

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.
  #23  
Old January 16th 04, 01:38 AM
Philip Nelson
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Default Skate technique USST two cents


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!
  #24  
Old January 16th 04, 04:36 AM
Derick Fay
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Default Skate technique USST two cents



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?
  #25  
Old January 16th 04, 06:24 AM
Ken Roberts
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Default Skate technique USST two cents

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.

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


  #26  
Old January 16th 04, 07:07 AM
Ken Roberts
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Default Skate technique USST two cents

Maybe I'm just not understanding what is meant by "cardiac output" here, but
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


  #27  
Old January 16th 04, 07:47 AM
Ken Roberts
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Default Skate technique USST two cents

Derick Fay wrote
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


  #28  
Old January 16th 04, 09:00 AM
Janne G
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Default Skate technique USST two cents

I have to say that you both have right in this question.
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.

Ken Roberts wrote:

Maybe I'm just not understanding what is meant by "cardiac output" here, but
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.


--

Forward in all directions

Janne G
  #29  
Old January 16th 04, 03:16 PM
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Default Skate technique USST two cents

In article , Mark
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

  #30  
Old January 16th 04, 04:22 PM
Mark Drela
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Default Skate technique USST two cents

Below is a more detailed writeup I cobbled together
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.




 




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