Ski Skating in cross country skiing
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Climbing up hills is a turn-off and deterrent for lots
of skaters trying out skating on the roads. Handling the hills is the biggest deterrent to enjoying skating for most
cross country skiers: Skiing fast and gliding long on the
flats is the fun part. Climbing up a hill is just a struggle, and
even after going over the top, it can leave our legs too burning and tired
to enjoy the next section of long gliding on the flats.
What can be done to survive climbing the hills well enough so we can
enjoy the rest of our skating?
The question is:
Slow -- How to skate up a hill slowly?
Here we analyze this problem from the perspective of biomechanics and
physics, and propose some solutions.
Why steep hills require higher forces
Here's a quick sketch of the problem:
Start with muscular Power output. The maximum power
which can be sustained for like 8-30 minutes for a particular kind of
skating equipment and technique has a rough correlation to the maximum
rate of oxygen delivery thru the lungs and heart and and circulatory
system all the way into the muscles engaged in delivering the skating
power. (For many skaters, this capacity can be changed thru a
well-designed training program -- or it will also change due to
continued lack of training).
Or . . .
Strategy 1a = Use equipment that can engage
more muscle mass to effectively deliver more power for propulsion
(without too much negative impact on other muscle moves which are
already delivering propulsive power).
The obvious method is to use poles to
help push, which engages more muscles in the arms and torso for
propulsion. This diverts some oxygen from other muscles, which reduces
their output -- though it has been found for skating that most people's
cardio-vascular system can be developed to deliver more total oxygen
volume and pressure to achieve a net gain from the use of poles. There
are also some losses due to the coordination of the leg-pushes becoming
less optimal -- not a trivial concern, given the great complexity of
skating motions even without poling. The amount of these losses
depend on the coordination capability of the skater (and making good
choices of which pole-versus-leg coordination methods to attempt).
But overall most skaters can survive climbing steeper hills if they use
poles to help.
Strategy 1b = Use non-intuitive moves that can
engage more muscle mass to effectively deliver more power for propulsion
(without too much negative impact on other muscle moves which are
already delivering propulsive power). Sometimes those moves require
greater complexity of coordination or precision of timing in order to be
effective -- so they are neglected on gentler terrain where they aren't
so necessary for success.
One example is to use a torso-shoulder
side-swing move, which requires careful timing -- even though "quiet
upper body" is simpler.
For skating up a steep hill, the main resistive forces
are gravity and gliding friction (also air resistance). Those forces are
roughly independent of speed, so the Power (measured in Watts) required
to overcome the resistance is proportional to the speed of climbing.
So the first strategy for sustainable climbing is to
reduce the speed until the Power required to achieve it is less than the
sustainable maximum power output (based mainly on the skater's current
capacity for delivering oxygen to the skating muscles).
Strategy 2 = Well-disciplined pacing. Learn to
avoid climbing too fast.
But when the climbing speed gets too low, other
problems arise. The main one is that the probability rises of failing to
control the gliding on the ski -- of "stalling out" -- then needing to
restart, perhaps along with a balance-recovery move, or recovery from
starting to slide back down then hill. If the probability and frequency
of "stalling out" gets too high, then there's too much time and effort
lost in handling the occurences of stalling -- and skating becomes
ineffective (and not much fun).
Generally, the slower the skate is gliding, the higher
the probability of "stalling out". The more the skate is aimed away from
the direction of overall forward motion, the higher the speed of the
gliding ski can be for a given rate of vertical climbing.
On the other hand, the more the glide is out toward the
side, the higher percentage of power output is dissipated into
overcoming gliding resistance, instead of helping move vertically up the
hill.
Strategy 3 = Aim each skate more out toward the
side.
There are two aspects of this low-speed gliding
problem: One is the average gliding speed over the whole stroke cycle,
the other is the lowest speed in some smaller part of the stroke. Having
a gap or low power spot in the stroke cycle could increase the chance
that the gliding speed will drop dangerously at some point in the cycle.
Strategy 4 = Improve control of
low-speed gliding without stalling out.
The tough problem: FG muscle fibers
I think the toughest thing that makes my legs "burn
out" from climbing up hills is putting high peak force loads on muscles.
High peak forces tend to engage the "fast glycolitive" (FG) or "slow
twitch" muscle fibers, the kind of fiber which is good for a sudden need
for high force, but which takes a long time to re-charge to be used
again.
Most of time while skating we use the "slow oxidative"
(SO) or "slow twitch" muscle fibers, which can be re-used many many
times in performance without needing to "re-charge" (provided they're
getting enough oxygen delivered to them thru the blood). When the force
demanded at a particular moment is too high for the SO fibers to
deliver, some of the FG fibers get recruited to help them out.
Each time my unconscious neuro-muscular control center
calls on some of these FG fibers to help climb a steep hill, there are
fewer "fresh" ones available to help out on the next hill, because more
of them are held back while waiting to re-charge. Finally they're mostly
"used up" for the day.
After "using up" most of my FG fibers, I can
still feel sort of OK while I'm skating on easy flat terrain, but the
next time I reach a small hill, it hurts now, because they're not there
for me, or because they're being forced to try to help out even though
they don't have much left to contribute.
Therefore:
what about Lactate Threshold?
Often people think LT is the big limiter on surviving
hills -- perhaps because it's a key limiter in lots of other skating
performance situations.
A few thoughts on that:
-
LT indeed could be a key limiter if the goal is to
climb up a long moderate hill (not real steep).
-
LT indeed could be a key limiter if the goal is to
climb up a steep hill fast -- like to try to keep up with
some other skaters. (But "surviving the hills" is about climbing
slow.)
-
Climbing fast could sometimes work as a way to try
to make it up over a hill without requiring high peak forces. The
problem is that it is often difficult to know in advance if it's
enough for the next hill. Then I find out that going fast is not
enough, so I have to slow down. But the hill isn't finished yet, so
my unconscious neuro-muscular controller starts recruiting FG fibers
to get me to the top the slower more reliable way. (So I end up
needing to use some techniques to avoid peak forces, anyway.)
-
Techniques to deal with Lactate Threshold when
skating long gentle high-speed sections are often very different
from the techniques to avoid high Peak Forces at low skating speeds.
Expert skaters on long steep climbs prefer the Peak Force
strategies.
One way to avoid the LT problem is to add more
different muscles, like Double-push technique uses the little-known "hip
adductors". But often the way to deal with Peak Force limits is to focus
on fewer muscles. Another strategy for Peak Force is to overlap the use
of different muscles.
The evidence of experienced inline skaters
climbing long steep hills is that they do not use Double-push stroking,
and they show a higher percentage of their stroke cycle time with both
feet on the ground (overlap).
I suspect for most experienced skaters on sustained
hill climbs, avoiding LT problems is mostly a matter of well-disciplined
pacing, not technique.
Well-disciplined pacing is usually achieved
after several experiences of the results of bad pacing.
But even after I've slowed my skating pace down as far
as I can (without stopping) there's still some need to use high Peak
Forces for climbing some steeper hills.
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Specifics
Most muscles can sustain higher force if they move
slower.
Muscles which can sustain higher forces in static
transmission than in active motion. They can transmit direct forces from
current moves by other muscles, or kinetic energy from previous moves by
other muscles.
Move muscles through a shorter range-of-motion
distance.
Muscles which are not strong enough to act alone can
still contribute if they overlap with moves by other muscles.
Percentage of stroke cycle time with
overlapping leg pushes is higher for climbing up a steep hill.
Learning to move slow takes creative practice. Find new
ways to go slower. Use slow skaters on your route as an opportunity to
learn, by following behind and copying their rhythm and moves.
turnover frequency
causes of turnover:
-
Moving slower tends to reduce frequency.
-
Moving thru a shorter range-of-motion distance
tends to increase frequency.
-
Focusing on fewer moves (by stronger) muscles tends
to increase frequency.
e.g. eliminate the inward arc and inward
knee-extension from Double-push.
e.g. eliminate also the (non-arcing) inward
hip-adduction push from Double-push: which makes it into classic
single-push. Instead overlap the Extension phase of the previous
leg-stroke with the Sweep-Outward phase of the next leg-stroke.
-
Overlapping major moves tends to increase
frequency.
-
The popular consensus is that for climing a steep
hill, turnover frequency should be higher than on gentle terrain.
results of turnover
Power = Force * Velocity
Power = Force *
Effective-Range-of-Motion-Distance * Frequency
That's the idea behind the "light and quick"
concept. But there's a temptation to move quicker than necessary to just
"survive" the hill -- so don't be afraid to experiment with "light and
slow" sometimes.
I suspect a better strategy is to give
priority to making the motions shorter, simpler, and more overlapping --
and invoke "quick" only if those are not enough.
-
Higher frequency tends to increase the percentage
of power which comes from non-intuitive reactive side-force moves,
instead of just obvious leg-pushes.
-
Higher turnover frequency in skating tends to
increase the percentage of power which is wasted in starting and
stopping recovery moves.
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