see also
[ under construction ]
Questions
The idea is that when skating up a hill you try to land your ski as
far up the hill as you have the sustainable strength to move your body
up onto your foot.
Lots of elite racers do this.
I think the idea is that you increase the vertical component
of your range of motion in your leg push.
My current thinking is that the physics of this really works and it's
important for efficiently getting up a hill.
Note this is a different view than I have about stepping
forward on flat terrain.
What makes stepping up so different from stepping forward?
- The vertical force-direction is mostly perpendicular to the plane
of motion of the skate-push, with the forward direction is mostly in
the plane.
It's magical to use sideways force to move forward --
in the same plane of motion. It's just inefficient to try to use
sideways force to move upward outside the plane.
- Speed is lower going up a hill, but the "magic" of
skating physics works best at higher speeds.
- Gravity is a special kind of force in ski technique, because it
comes with a well-defined potential energy function. That
means that gains in fighting gravity can be easily transmuted into
other useful factors.
Video observations
Looks to me like Fulvio Valbusa is one who uses little forward step when
doing V2 on the flats, but shows a distinct upward-and-forward step when
he switches to V1 to go up a hill -- see Valbusa
1 video on JanneG's website.
For stepping up on a rather steep hill see Carl Swenson in the last 7
seconds of Swenson
1 video on JanneG's website.
Pushing to extend the leg can be out to the side (like in the
skate-push phase of V2) -- which is magically transmuted into forward
motion by the angle of the ski. Or the leg can be extended to push
downward, which then lifts the hips forward and upward -- which
lifts the weight of the skier's upper body upward (like in the first
part of the glide phase in V2).
In V2 skate the direct upward lift of the upper body then allows its
weight to drive a stronger pole-push. But when climbing up a hill,
moving a substantial portion of my body weight upward has value just in
itself -- since fighting gravity is the biggest obstacle there.
Seems like many elite racers do this.
See the arguments above under stepping up
the hill.
One idea is to only apply enough side-push to keep forward motion
going, and put the rest of the leg-push into directly lifting the upper
body. To get a bigger range of motion for emphasizing the vertical
component, the leg-push must be preceded by stepping the foot way up the
hill.
Disadvantage of direct lifting: After stroke with substantial
direct lift, the hip is higher than if the push had been all out to the
side. So the next ski typically lands with the hip higher and the
knee less flexed. But the range-of-motion for the next skate-push
is largest when it starts from more knee flex.
I suppose you could allow the hip and upper body to drop
during the leg-push, which would apply more skate-push force. But
when climbing up a hill, the main point is to keep moving most of the
body-weight up, so dropping it down seems counter-productive and
inefficient.
A better response to this disadvantage is just to be
careful not to "over-do" it on direct lifting on one side --
more than the other side is ready to handle effectively.
Video observations
In some older videos of Daehlie in my collection, he seems to
emphasize side-skate more on his hang-side and direct-lift more on the
recovery-side.
I see a large percentage of leg-push going into direct lifting when
Carl Swenson climbs a rather steep hill -- see the last 7 seconds of Swenson
1 video on JanneG's website.
Puzzle
Here's the puzzle: The full stroke-cycle for
maximum-effective-work Open Field skate
is: (1) land pole-push-side ski + glide + lift hips and upper body
(2a) start pole-push and help power it by dropping hips and upper body,
(2b) start skate-push and continue pole-push (3) land recovery-side ski + glide, (4)
skate-push + pole-recovery. Five phases, but here numbered as
four.
When going up a steep hill, it's important to change the stroke
cycle:
(a) minimize or eliminate phases with low-power and no-power
"dead spots"; and
(b) focus on the high-power phases with most muscle mass with
effective forward-motion leverage; and
(c) shorten the range of motion of some muscles to their strongest
and safest sub-range.
The reasons for these changes are that going up a hill
requires more power -- to simultaneously fight gravity and keep up
enough speed to avoid lapsing into a non-skating herringbone. And
more power requires higher average force during the stroke.
The danger is that some muscle might be pushed to try
to deliver either a peak force or a sustained rate of force beyond its
safe limit -- and then have its performance degraded afterward.
That's one reason for (b), to focus on the big muscles that can handle
more force. And the reason for (c), since even the big muscles
have weaker and stronger parts of their range of motion. The
justification for (a) is that if one phase is delivering little or no
power, then the other phases have to deliver even higher forces -- in
order to keep the average high enough to keep moving up the hill.
To modify the Open Field skate cycle for steep hills, the obvious
changes are:
- minimize or eliminate phase (3), the passive glide on the
recovery-side ski.
- minimize phase (1), the passive glide and lifting of hips and
upper body on the pole-push side.
For a steeper hill, the next change is:
- eliminate phase (1), the passive glide and lifting of hips and
upper body on the pole-push side.
And that takes us to V1 offset.
So now we have three phases remaining: (2a), (2b), (4).
The next big choice in the stroke cycle is: Should the start of
(2b) skate-push be delayed to after the start of (2a) pole-push? -- like
for maximum effective work in in the V2
hints and Open Field skate hints?
Or should the two start pretty much simultaneously?
(A) If the start of (2b) is delayed until after the strongest part of
(2a), then the time on the pole-push-side will tend to be longer, since
it has two phases instead of one.
(B) If the starts are simultaneous, then the time on the
pole-push-side will tend to be shorter, because there is much more force
being applied, but the range of motion is not much larger than the
recovery-side.
Video observations
In some older videos of the great Bjorn Daehlie in my collection, he
clearly takes a shorter time on the pole-push-side than on the
recovery-side.
In the last 6 seconds of Carl Swenson climbing a rather steep hill
using V1 technique in the Swenson
1 video on JanneG's website, I see pretty near the same time spent
on each side -- but I used to think it was slightly longer on the
pole-push side -- now it seems like he's to smooth that it's hard to
tell exactly when he finishes one leg-stroke and when he starts the
next.
Responses to the puzzle
For getting up a steep hill, the problem is to keep applying enough
force to keep going upward in a skating motion, but avoid peak force
demand on a specific muscle.
(A) One idea is that the "weak link" in the stroke cycle is
the recovery-side leg-push, since it gets no assistance from the
pole-push. Therefore to spread force most evenly, it is better to
have less overlap between leg-push and pole-push on hang-side. So
make up a separate new phase for the most intense portion of the
pole-push (at initiation) -- with little or no leg-push yet. Then
make the hang-side leg-push (with minimal pole-push assistance) about
the same as the recovery-side leg-push.
Result: a more even distribution of direct push-force over the
stroke cycle, less variation in the skier's speed -- and slower turnover
cadence. Hang-side time longer than Recovery-side.
This sounds like Lee Borowski's breakthrough idea for
expert V1 on page 30 of The New Simple Secrets of Skating (2001) -- and
he closes by saying that the pole-push-side ski will glide longer than
the other.
(B) Another idea is: Don't bother about variations in my speed,
as long as I don't stall out and stop skating. Fully overlap the
leg-push and pole-push motions, which results in much higher force on
the hang-side. So the speed is much higher at the end of the
hang-side, and much lower at the end of the recovery-side.
Allowing the speed to slow down on the recovery-side is a legitimate way
in physics to "assist" the leg-push on the recovery-side (it's
like an "inertial" force) -- so the recovery-side leg is not
over-burdened.
Result: uneven distribution of force and speed over the
stroke-cycle, but peak forces no more than for (A). Speed
variations produce slightly higher average air resistance drag than (A)
-- faster turnover cadence. Hang-side time shorter than Recovery-side.
Key point: Physics says that it's easy to shift forces around
the stroke cycle to assist or burden different phases (especially when
playing closely with gravity-force).
Turnover (cadence) and Power
There's no doubt if you make three pushes in a shorter stroke-cycle
time, you're delivering power at a higher rate than if you made the same
three pushes (two leg and one arm) in a longer stroke-cycle time.
So clearly (B) delivers more power.
But up a steep hill, that might be a higher power rate than is sustainable
for an endurance performance. In that case it is critical to find
a way to generate power at a lower rate like (A). Can we modify
(B) to do less?
Yes. If each leg-push is made with a less force, then the power
burden will be less. Due to the magic of skating physics, the
range of motion can be adjusted by choosing the appropriate angle of the
ski.
If each muscle pushes with less force, but more frequently, method
(B) can handle the same power burden as (A), but with lower peak muscle
forces.
The only drawback of higher cadence is the extra work needed recover
each leg back in underneath more times. But this uses different
(opposite) muscles from the ones that power the primary skate /
"direct lift up" pushes. So while leg-recovery does use
some energy, it does not add significant burden against the critical
specific-muscle limits on uphill skate performance.
Therefore looks to me like (B) is the more effective way to climb a
steep hill: make the leg-pushes as continuous as possible, and
make the pole-push overlap with the leg-pushes as much as possible --
not try to put much of the pole-push into a "gap" between
leg-pushes.
Video observations
First 3 seconds Swenson
1 video on JanneG's website: Carl Swenson seems clearly to be
starting his leg-push as soon as he sets down his hang-side ski -- no
"gap" for the pole-push.
Start of PerElof4
video on JanneG's website: In the first two hang-side strokes,
Per Eloffson starts his leg-push as soon as he sets down his hang-side
ski
Per Elofsson's hang-side arm and leg are pushing down in synchronized
alignment in the EloffsonSlomo
video on JanneG's website.
Note the fast cadence by Rene Sommerfeldt when he switches to V1
after 16:00 seconds into the Sommer1
video on JanneG's website.
More arguments for (A)
- Since the pole-push can deliver a big upward-push force on the
body, especially at its start, it makes sense for to use it to take
on the "burden" of a distinct phase in the stroke cycle.
This enables the stroke cycle to take a longer time, so the average
power over the stroke cycle delivered by each leg muscle is lower,
even though the power rate while actively pushing is the same -- so
there is less lactate accumulation in the leg muscles.
- the pole-push is normally a longer motion than the leg-push, so it
has to "leak" beyond the time of the skate-push at one end
or the other.
Objection to (B)
But in the V2 hints and Open Field
skate hints, simultaneous
start resulted in loss of effective work.
Answer to objection: That's because there's several up-and-down
movements of the hips and butt in V2 and Open Field skate. So it's
important to time the start of the skate-push at when the hips are low,
because that's when the sideways range of motion is largest.
But in offset V1 up a steep hill, there should be very little
downward motion of the hips and butt. They should either be moving
upward, or holding steady at the same level. The reason is that in
going up a steep hill there is already so much burden on the
"upward lift" muscles that you do not want to add the burden
of making the same lift twice.
Also since a large percentage of the leg-push force is directed
downward (for direct lifting of the upper
body), the loss of range of motion out to the side is less important
than on flat terrain.
Also, since the main problem on a steep hill is moving the weight of
the body vertically upward, it is counter-productive to try to help
motion by moving a big portion of body weight downward (by leaning the
upper body on the poles and dropping the butt -- to help the
pole-push). If you're moving the upper body down to move the lower
body up, the net gain is much less than if you just directly
lifted up the upper body. So there's much less benefit in using up
and down motion of the hips and butt to make pole-push force larger.
Therefore in V1 up a steep hill, it doesn't matter so much exactly
when the skier starts the leg-push relative to the pole-push.
There is little reason to delay the start of the leg-push. Waiting
to drop the hips and butt a little further before starting the leg-push
has little benefit.
So why not start the leg-push as soon as possible in the stroke
cycle?
why not start the pole-push at a different time?
Why start the pole-push at the moment the hang-ski lands?
Proposed analysis: Since there are only two leg-pushes per
complete stroke cycle in V1, and each leg-push goes into a skate-push,
the pole-push is essentially all arms and abdominals, not from potential
energy supplied by the leg lifting the butt.
So if the pole-push and pole-push are essentially muscularly
independent, why does it matter how they are synchronized?
Why not have the pole-push overlap halfway across both
leg-pushes?
Why not put the strongest part of the pole-push into a gap
between the two leg-pushes?
some possible answers:
- putting the pole-push halfway across both would smooth out the force over the
stroke-cycle. Larger variation in velocity results in higher
average air-resistance force.
(true, but this effect is not large at the low
speeds on steep
uphills)
- down-force is valuable during the skate-push to help the edge dig
into hardpack snow. The down-force of the pole-push offsets
the weight of the skier's body on the edge of the skate-push
ski. The down-force component of the pole-push is largest at
the start of the pole-push -- so timing that start during a gap
between skate-pushes is the best way to safeguard edge-bite for the
skate-push.
(maybe so, but then why use this timing in soft snow
where edging is no problem?)
(But going up a steep hill, much of the leg-push of
an elite racer is downward as a "direct lift" of the butt
and upper body, not so much a "skate" to the side -- so
edge-bite is less important, and anyway the greater downward component
of the leg-push already supplies extra help for the edge-bite)
- it's just less bother to coordinate things if the pole-push is
synchronized with one of the leg-pushes (or at least its start or
its finish is synchronized with something else). If there's no
significant advantage to de-synchronizing (see Classic striding),
then might as well synchronize.
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