Pole Length Recommendations

32 degrees wrote:
longer poles = more power ... what about physics and physiology of it?

Surely at some point of increasing pole length, you'd see less power. But
what "underlying logic" drives the trade-offs?

My short answer is that it depends on which muscle groups you're emphasing
for your poling. If you're emphasizing arms and shoulders and upper
abdominals, then shorter poles enable better "velocity matching" for higher
speeds on gentle terrain. If you're emphasizing lifting the upper body high
(by the leg and back muscles) to "fall" onto the poles, then longer poles
gain more gravitational potential energy and better transmission of it, from
a larger range of motion distance of the big leg-extension muscles -- but if
the poles are too long, then transmission efficiency suffers.

By this argument it's not so much Skate versus Classic, but the style of
Poling that drives optimal pole length:
* Single-poling or "herringbone" skate does not allow time for much upward
extension, so it focuses on arms and shoulders, and benefits from shorter
poles.
* Open Field Skate (V2A) and slower-cadence V2 use big upward extension and
long poles, and seems to me
* that same logic applies to pure classic double-poling, provided you've
_trained_ lots with longer poles.
* Jump Open Field Skate (like Bjorn Lind for a few strokes in his Gold medal
Final at Torino 2006) shows the maximumally awesome upward extension I've
seen in competition skating, and so would benefit from the longest poles (if
he could just keep it up thru the whole race).

Like Andrew Lee said, try some experiments. The only thing I'd add is that
to be more accurate you'd likely want to practice several days (or weeks?)
with a new experimental pole length, so your muscles and unconscious neural
control centers will have time to better adapt themselves and optimize for
it. The hassle of that makes me glad for the tips offered by rm to observe
while you're skiing with your current poles.

more details below.

Ken
____________________________________________
The physics and physiology of double-poling by serious racers is pretty
complicated. Someone could make a computer simulation model at the level
of muscles and joints -- like has been done for simpler propulsive
techniques like seated bicycling in the last 10 years or so -- and then use
the simulation to play around with that to get a sense of which input
factors are the main drivers of optimal pole length. If anything like this
has been done, I'd love to hear about it. For now I'm guessing it hasn't.
But perhaps there is becoming available good enough data (like from video +
position + force + torque sensor studies of rollerskiing on a laboratory
treadmill) to provide some important inputs for such a simulation.

While waiting for that, some thoughts . . .

Here's some possible sources of propulsive power for pure double-poling:
(a) contraction of the arm and shoulder and abdominal muscles to push on
and directly move the pole-handles backward and downward.
(b) gravitation potential energy from the mass of the body pressing down on
the poles.
(c) kinetic energy of the upper body "dropping" down on the pole handles
from above.
(d) pulling the mass of the feet and lower legs upward in the early phase of
the pole-push.
(e) thrusting the mass of the feet and lower legs forward near the end of
the pole-push.

My analysis:
** Ignore sources (d) + (e), because they work equally well (or not?) with
any halfway-reasonable length of poles.

** source (a) tends not to work as well if the poles are _too_ long because
then the pole tip would have to be planted further behind at a lower angle
so they could operate in a non-extreme segment of their angular
range-of-motion. But (by trigonometry) the lower pole angle requires that
the muscles move through a larger segment of contraction range in order to
match the same distance of the skis and skier moving forward over the
ground. Which means the muscles must contract with a higher velocity in
order to "keep up" with the high ground speed typically used by racers for
pure double-poling on gentle terrain. At high ground speeds this required
muscle velocity is outside the "sweet spot" of the muscle's (aerobically
sustainable) power-force-velocity curve. (sorta like a car engine has a
power-torque-rpm curve) -- so then the (a) muscles could produce higher
sustainable power with shorter poles that allowed a higher + more vertical
pole angle.

** the lower the shoulders are to the ground, the more the contraction of
the upper abdominal muscles of (a) is "aimed" backward and downward.
(another advantage of shorter poles over longer.)

** (b) is the key source of power where longer poles can help. Gravity is
not a "free lunch" -- exploiting it on flat ground requires real muscular
work, using the knee-extension, hip-extension, and back-extension (and
sometimes ankle-extension) to elevate the masses of various parts of the
skier's body, during the "recovery" phase between the pole-pushes. Someone
in the last few months on this newsgroup mentioned a recent study which
indicated that there muscles supply more than half the power of pure
double-poling. Seems very believable to me. The propulsive work done by (b)
is basically roughly
Work = Grav * Mass * Dist * Transm
where Grav = a constant based on earth's gravity; Mass = the amount of
masses of different body parts that got elevated during the "recovery"
phase; Dist = the distance that the masses drop while pressing on the pole
handle; Transm = transmission efficiency percentage.

Assuming you've got lots of muscle mass in your obvious big leg-extension
muscles well-trained from other sports and general living, then increasing
the "Dist" factor is the easy way to exploit more of that capacity for
skiing double-poling. Roughly speaking the Dist amount which the Mass can
descend while pressing on the pole handles is proportional to the length of
the poles.

The remaining variable factor is "Transm" the transmission efficiency -- and
I think it's the point where "getting over the poles" comes into play. Kinds
of transmission losses get tricky, and I'm not sure how to prove this, but I
think the critical point for transmission is that the arms must hold
stable -- like pretty much move "rigidly" with the shoulders) through the
first half of the pole-push -- the elbows move downward at least as much
distance as the shoulders, the hands move downward at least as much distance
as the elbows. If the shoulders move downward farther than the hands, then I
think you lost some of the power available from gravitational potential
energy.

I think most people find out that they fail this "rigid transmission" test
if their hands start too high, because their poles are too long.
. (Or if their hands start too far out in front or too far out to the
side -- usually because they're trying to focus on getting more power from
their arm muscles instead of gravity.)
When the poles get _too_ long, the losses in Transmission efficiency more
than cancel the gains in gravity Distance.

** (c) is closely related to source (b) and somewhat also (a). The key point
is that physics says that it can help to start downward motion _before_ the
pole tips hit the ground. (and I've seen videos showing World Cup skiers
doing this in double-poling.) The early move builds kinetic energy, and
then when the pole tips hit the ground this kinetic energy can transmitted
thru the arms to the pole handles and into the ground to help push the skier
forward.

Now there's a clever way to try to exploit source (b) but keep shorter
poles: Turns out the Kinetic Energy built from starting to drop the mass of
skier body parts early is equal to the gravitational potential energy built
from raising their masses higher than they will be when the poles hit the
ground. So you can use the same big leg-extension (and other) muscles to
raise body parts higher as for (b), but avoid the need for longer poles by
first converting it into downward kinetic energy.
. (Or you could jump even higher -- get your whole body off the ground --
exploit those big strong leg-extension muscles even more fully -- but that
introduces a different kind of power loss.)

I think the problem with overdoing this trick is that the Transmission
efficiency suffers, because higher early Kinetic Energy means higher impact
force when the poles then hit the ground. Higher losses in compressing snow
under the pole basket, but I think the bigger losses from the arms tending
to collapse, the hands and elbows failing to move down "rigidly" with the
shoulders in the first half of the pole-push.

So even with knowing and using trick (c), longer poles still help some for
the "upward extension" style of poling. And trick (c) is a key reason that
poles are not selected even longer for exploiting source (b).

Ken

Well there sort of is a 'pole stretcher'. I cut a wood dowel that just fit
inside the grip, to lengthen a pair of poles about a 1/2".
But you're right, better to measure twice and cut once to begin with.....

--

Paul Haltvick
Bay Design and Build - LLC
Engineering, Construction and Information Technology Services
FSx Midwest - Fischer / Swix Racing

Any thoughts??

Bill K

Just remember that there is no such thing as a pole stretcher.

Thanks to everyone for your kind help and suggestions. The reason I
asked this question in the first place was that after being away from
skate technique for a number of years because of injury, I got back
into it at the end of last season. In the mean time, I'd sold off all
my skate gear so I've been in the process of reaquiring skate stuff.
I bought a pair of poles in the Autumn, Swix CT3. Got them at the
recommended 165 cm, but I was never comfortable with them. They CT3s
seemed to have a heavy swing weight and were annoying when skiing a
brisk V2. I also felt like I had to stretch a bit to bring my hands
high enough on steep hills.
So after a few weeks of skiing with them, trying to talk myself into
liking them, I went searching through the closet and came up with a
pair of old mis-matched (one Swix Star, one Excel Galaxy) that were
just a bit shorter, 162.5. I tried them, and liked them much better
than the CT3s. So then I had to decide whether it was the weight or
the length of the CT3s that was bugging me, thus my question to the
group.
So what did I do? I did what any red-blooded American consumer would
do. I went out and got a new pair of Swix Stars! As it turns out,
the swing weight is so much better with the Stars that V2 is really
snappy despite the extra length, and I decided I can live with the
extra length on hills for whatever extra power I'll get on V2-
Alternate sections.
Moral of the story? Don't cheap out on equipment! Anybody want to
buy set of Swix Carbon CT3 poles, cheap?

BK