Ski Skating in cross country skiing

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Overview

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.

Theory of limits on Climbing Hills

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:

  • Using skating techniques that get me up the hill without putting high peak forces on any muscles will enable me to keep feeling the fun out there for longer time, and burn more calories in that longer time.

 

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

  • Concepts of Power and Turnover relationship:

Power = Force * Velocity

Power = Force * Effective-Range-of-Motion-Distance * Frequency

  • Higher frequency tends to make it easier to deliver the minimum required power output with lower peak forces.

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.

 


 

Ideas + Tips for Climbing Hills

 

[ to be added ]

 

more . . .

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