what's here
intro
phases R3b P0 P1 P2 P3 P3b R0 R1 R2 R3
variations
-
high turnover frequency
-
very steep hill
-
jump skate
see also
[ under construction ]
intro
see also:
how the moves have changed from 1997 to 2007
Not much: most key observations are the same.
Differences in observations:
2007: generally higher hip position, less tilting of
the hip-foot line away from vertical at the finish of the leg-push.
2007: hips "rock" move evenly from side to side: tilted
toward P-side at end of P-side push, toward the R-side thru near the
finish of R-side push. 1997 the hips tilted mostly toward the R-side,
but briefly tilted to the P-side around the time of set-down.
2007: P-side shoulder starts moving back toward the
R-side earlier, looks like it "turns away" from the leg-push and
pole-push before they've finished. 1997: P-side shoulder stays outside
of its hip longer -- at least until the P-side hand passes by its leg --
before stargin to move back toward the R-side.
2007: Shoulders start rising a little earlier as move
from P-side across to R-side. 1997: shoulders hold lower longer as move
from P-side across to R-side.
Underlying concepts:
2007: Less concern to derive maximum propulsion from
the skating leg-push (with its strong side-to-side emphasis). More
willingness to use more of the leg-extension for vertical motion to
drive the start of pole-push. Less concern to exploit the pole-push to
its finish - (willingness to compromise the finish). More concern to
increase turnover frequency.
Tilting the pelvis toward the leg-push enables
a larger leg-tilt angle without a longer leg-push distance.
1997: Desire to exploit the skate leg-push fully, from
set-down underneath thru large distance extended out to the side, and
full motion of the upper body away from the push. Desire to exploit the
pole-push to its finish, use the P-side shoulder to keep driving the
pole-push to its finish. Less concern with turnover frequency.
Tilting the pelvis away from the P-side
leg-push Extension phase enables easier exploitation of the obvious
leg-push with "straight" hip-extension like bicycling.
my analysis
The 2007 style is faster for pro racers because:
-
using leg-extension power to drive poling instead
of skating takes some downward force off the ski, so there is less
friction (especially in softer snow).
-
the average edging angle of the ski is less, so there
is less friction (especially in softer snow).
-
higher turnover frequency exploits the emphasis on
poling (and on the starting phase of pole-push). High turnover is not so
much of an advantage for the skating leg-push.
-
the finishing phase of the pole-push isn't worth so much
anyway.
The older style might be better for amateur "mid-packers"
because:
(a) They don't spend their summers practicing hours and
hours of poling;
(b) Their back muscles can't keep up with the quick
recovery needed to exploit high turnover frequency in poling;
(c) Their "Sweep" muscles are not trained to be able to
still get a lot out of the shorter length of skating push.
(d) Tilting the pelvis toward the P-side during the
Extension phase of the P-side makes it more difficult to exploit the obvious
"straight" push with "bicycling" hip-extension muscles. (Better for people
willing to train muscles all summer long for a special "diagonal".)
definitions
P-side = Poling-side (also known as "strong side" or "hang side")
R-side = pole-Recovery side or just Recovery side (also known as "weak side"
or "glide side")
[A] = high priority for speed and power.
[B] = significant priority for speed and power.
[C] = lower priority for speed and power.
P0, P1, P2, P3, P3b are "phases" of the P-side push.
R0, R1, R2, R3, R3b are "phases" of the R-side push.
P3b overlaps in time with R0 + part of phase R1, but
R3b does not overlap in time with phase P1.
R3b - drop toward P-side pole-plant + set-down
position at start
full body weight on R-side foot, P-side foot in the air, both
pole tips in the air -- with P-side shoulder and P-side hip in their highest
position.
video observations at start:
front view:
?? Why ??
Pelvis tilted toward R-side. (note this is different
from how lots of pro racers do it in V2 skate)
?? Why ??
?? Why ??
side view:
?? perpendicular to the ground surface versus vertical
in gravity ??
?? Why ??
Not straighter than 90 degrees. Not with the hand
extended way out in front.
?? Why ??
moves
P-side knee starts moving outward to P-side.
?? Why ??
-
P-side shoulder drops diagonally toward P-side.
-
P-side arm starts pushing down already, though the P-side
pole-top is still in the air.
-
R-side leg continues its Extension push to completing --
(its Sweep push is already over)
P0 - pole plant + set-down P-side foot
timing
P-side knee starts moving outward to P-side.
?? Why ??
Why? Because there's no physical or biomechanical
significance to the exact relative timing of the two pole hits or the overall
pole push moves. It's just not convenient to have the P-side pole tip hit
earlier, and it's often convenient for the R-side pole push to finish earlier.
position
front view
?? qqq
?? Why ??
If leg fails to achieve "toe extension" at the end of
it's push, that's a symptom that: (a) its foot was not set down far enough back;
or (b) the shoulders were not dropped quickly enough; or (c) the leg-push was
aimed too much out toward the side.
?? Why ?? Key is complete transfer of body weight to
land on the poles and drive the initial phase of the pole-push. Any weight
remaining on the R-side foot at the moment of pole plant takes away from the
force (though actually if it comes onto the poles soon afterward it's still
pretty good).
?? qqq
?? Why ??
Maybe just a little outside is OK.
?? Why ??
?? qqq
?? Why ??
?? qqq
?? Why ??
?? qqq
Except perhaps on a very steep hill.
?? Why ??
foot-aim view
?? qqq
Except perhaps on a very steep hill.
?? Why ??
?? qqq
?? Why ??
side view
?? perpendicular to the ground surface versus vertical
in gravity ??
35 degrees might be better.
?? Why ??
?? qqq
?? Why ??
key point is: Not too far forward.
?? Why ??
P1 - just after set-down
moves
P-side shoulder moves down and sideways as it pushes on the
pole.
P-side leg helds stable as it transmits side-force to the
foot-ground contact while "catching" and stopping the sideways motion of the
upper body + pelvis.
Phase P1 starts at set-down.
Phase P1 ends when the medial hip-knee rotation move.
?? what about P-side hip
?? what about forward pelvis rotation ??
position at end
front view:
?? qqq
?? Why ??
foot-aim view:
Stability of hip-abduction.
?? qqq
?? Why ??
side view:
?? elbow bend and shoulder bend stability (stable transmission
of upper body weight landing on poles, with no collapse)
P2 - medial hip-knee rotation move
moves
Key moves are the "Sweep" moves of medial hip-knee rotation and
ankle-pronation. There might possibly be some active hip-abduction move, but it
would be pretty difficult to see that in video.
?? The pole push transitions from upper body push to arm-push.
(or is from static transmission to active pushing ??
?? when does pole-push finish ??
Phase P2 starts when the medial hip-knee rotation move starts.
Phase P2 ends roughly as the emphasis on medial hip-knee
rotation transitions to emphasis on Extension push.
position at end
front view:
P-side foot outside from underneath its knee.
better seen in foot-aim view
?? Why ??
P-side shoulder still outside P-side hip - (but not much
sideways motion any more) [B]
?? qqq
?? Why ??
P-side shoulder lower than R-side shoulder. [B]
foot-aim view:
P-side ground-contact point significantly outside from
underneath its ankle. [A]
?? qqq
?? Why ??
P-side foot significantly outside from underneath its knee. [A]
?? qqq
?? Why ??
P-side knee roughly underneath its hip - (definitely inside)
[A]
?? qqq
?? Why ??
side view:
P-side hand moving back to pass by the P-side leg a little
higher than its knee. [A]
?? qqq
?? Why ??
P-side heel still on ground.
P3 - extension move
?? Phase P3 starts roughly as the emphasis on medial
hip-knee rotation transitions to emphasis on Extension push.
Phase P3 ends when the heel of the foot comes up off the
ground.
?? when does pole-push finish ??
?? when is the forward pelvis rotation ??
moves
?? qqq
?? Why ??
"Turning away" from the P-side pole-push before it
finishes is just a necessary adjustment rhythm of the side-to-side upper body
motion in order to exploit power from that motion with leg-pushes at a higher
turnover frequency.
?? It's not a big deal if the shoulders "hang on" to
help drive the P-side pole-push longer.
?? What's bad is to start turning the shoulders away from the P-side even
earlier.
Why turn away now? Compromise: Higher turnover
frequency and more precise timing of Side-to-Side upper body motion with higher
frequency versus Maximum exploitation of finish of pole-push.
?? perpendicular to the ground surface versus vertical
in gravity ??
Skiers who have not done lots of training of their
back muscles to handle this should use a smaller forward-lean angle which they
can sustain without injury.
?? Why ??
It's not a big deal if the shoulders stay low
longer to keep driving the P-side pole-push longer. What's bad is if the
shoulders never get down low enough at all.
Why? Compromise: Higher turnover frequency and
perhaps more vertical motion of shoulders to drive start of next pole-push
versus Maximum exploitation of finish of current pole-push.
Why? Because there's no physical or biomechanical
significance to the exact relative timing of the finish of the two pole-push
moves. Often it's just convenient for the R-side pole push to finish earlier.
position at end
?? qqq
?? Why ??
Note this is different from how most pro racers tilt
the pelvis in V2 skate. And it's not how some very fast skiers ten years ago did
V1 skate.
Why? (a) Tilting the pelvis toward the leg-push
enables a larger leg-tilt angle from a higher overall hip position -- without a
longer leg-push distance. Larger leg-tilt angle implies that a higher percentage
of the force and work is applied immediately for forward propulsion; and
(b) If the P-side hip is lower at the start of the R-side push, then some of the
work of raising the weight around the pelvis can be performed by
(under-utilized) pelvis-tilt muscles instead of (over-utilized) leg-extension
muscles -- though the leg-extension muscles must still transmit the work
of the pelvis-tilt muscles.
(The problem with an overall lower hip position is
that if you set down the foot underneath the hip, then it takes a longer
distance and time to get to full extension -- so lower turnover frequency. But
if you try to get a shorter pushing distance and time by setting the foot down
further outside, you miss the best configuration for the Sweep move, which
transmit the highest percentage of its work from into forward propulsion.)
Why not? The disadvantage of the tilting the pelvis
toward the leg-push is that it makes it more difficult to use the obvious
"straight" hip-extension move which is easily trained by bicycling and running
(and by classic cross-country ski striding).
V1 versus V2 (at higher turnover frequency): In
V1 skate, if the P-side push finishes with pelvis tilted away toward the R-side,
this is good for exploiting the obvious straight "bicycling" hip-extension move.
But then the R-side leg-push starts with the hip lower, with the problems
described in the parenthetical note above. In V2 skate the R-side hip being low
at the finish of the P-side push is not a problem because the distance or time
of skating aspect of the next push on the other side is not critical for
turnover frequency anyway. What is critical is the combined time of poling and
skating -- but there's more than enough time to get through the Sweep phase of
the skating push while getting up into the high position for the pole-push of V2
before going into the Extension phase of the push. So high-turnover V2 is free
to take the "easy" way of tilting the pelvis away from the Extension leg-push -
(because the frequency of high-turnover V2 is not as high as the frequency of
high-turnover V1). But in V1 skate the Sweep phase of the next leg-push must
begin immediately, so there is no free time available.
?? unless it's a very steep hill.
?? Why ??
?? qqq
?? Why ??
P3b - P-side toe-push + set down of R-side foot
moves
Phase P3b starts when the heel of the foot comes up off the
ground.
Phase P3b ends when the whole foot loses contact with the
ground.
Phase P3b overlaps with Phases R0 and R1. There is a period
while both feet are on the ground at the same time.
timing
?? qqq
?? Why ??
Note that this is different from the transition from
the R-side push to the P-side push (phase R3b to phase P0, where the point is to
avoid overlapping feet on the ground).
?? qqq
?? Why ??
position
?? qqq
R0 - set down of R-side foot
timing
see under phase P3b.
position
set down close undernneath
not too far foward
flat foot
knee perhaps aimed out
focus is on initial "catch" of sideways motion from the
P-side push.
some overlap with phase P3b
Phase R1 starts at set-down.
Phase R1 ends when the medial hip-knee rotation move.
position at end
?? [ see under phase P1 ]
?? Hip-Shoulder angle
?? hip abductor stability [A]
R2 - Medial hip-knee rotation.
Phase R2 starts when the medial hip-knee rotation move starts.
Phase R2 ends when the medial hip-knee rotation move ends.
?? Phase R2 ends roughly as the emphasis on medial hip-knee
rotation transitions to emphasis on Extension push. ??
but is there really a transition? or are the Sweep and Extension moves
overlapping more on R-side?
shoulders stop moving sideways toward R-side, start moving
sideways toward P-side.
Hip abductor stability [A]
Medial Hip-Knee Rotation [A]
Ankle pronation [A]
P-side hip moving up.
(Heel down)
R3 - Extension
Phase R3 starts roughly as medial
hip-knee rotation ends.
Phase R3 ends when the heel of the foot comes up off the
ground.
?? where is forward pelvis rotation?
Extension move
Hips move upward, especially P-side hip.
P-side hip moves up.
Shoulders rise upward.
position at end
P-side hip above R-side hip: two advantages: (a) larger
leg-tilt angle; (b) uses muscles to lift part of upper body other than
(over-utilized) leg-extension moves.
?? Hip-Shoulder angle
R3b - drop toward P-side
see above at the start of
the stroke-cycle for Phase R3b.
high turnover frequency
??
less side-to-side
less up-down
because just less time
very steep hill
??
set down foot a little outside from underneath its hip
hands and arms don't push to full follow-through.
but
do keep some drop of upper body weight onto P-side
pole-push.
do keep a little side-side motion.
P-side shoulder move only slightly outside its hip.
do push both legs to full extension.
do keep a strong medial hip-knee rotation move in both legs
V1 jump skate
typically used in high force + high turnover frequency
situations. (e.g. acceleration up a hilll).
Note that V1 jump skate is different from Open Field Skate jump
skate.
why the jump?
you want to get some effective contribution from the Sweep
muscles (therefore cannot set down the R-side way outside its hip).
you don't have time to wait for the leg-tilt angle to get large
enough so that the Extension push would be more sideways.
Therefore a significant component of the leg-extension force is
aimed downward, which raises the body upward.
Since it's a very strong push in a high-force situation, the
body is actually lifted all the off the ground. This result can be made easier
by specifically lifting the P-side hip and P-side higher.
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