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exploiting the head loop in V1 skate
Everybody who's looked at a video of an elite World Cup racer doing V1 skate
(a.k.a. offset, paddle-dance) up a hill has noticed that in a front view the racer's head makes an obvious loop. Today I think I figured out a detailed understanding of how this loop enables them to go up hills easier and faster. And how I had gotten the timing of my head loop all wrong in my own V1 video on Sunday. The explanation is long and tricky . . . There's four parts to the loop, and they're not what I thought they would be. But getting this loop right is like "free gasoline" for my skating up hills. (Even if you don't believe the loop has any benefit, there's an valuable surprise in the fourth phase below.) Here's how I now understand the head loop: V1 skate has a "hang" side (where I push down and back on the poles) and an "off" side (where I recover my hips and poles up and forward). On each side I need to further break down the skate leg-push motion into two phases: the first phase where ski lands in the snow and glides mainly in line (with also a sideways push by the hip abductor muscle), and the second phase where it pushes mainly out to the side (and to the back some too), and also glides in-line. So the leg-pushes of the full V1 stroke cycle have four phases: Hang1, Hang2, Off1, Off2. Here's what I see happening in each one: Hang1 -- focus on pole-push down: Head and shoulders are quickly come to a stop, transferring their previous downward momentum to the arms and poles. Arms move down to the skier's waist -- both transmit the "inertial" force from the dropping head and shoulders to the poles, and add direct force of their own. Hips and knees are fairly quiet in this phase. Some push on the ski out to the side by the hip abductor muscles, which gets the ski more on edge. Hang2 -- focus on leg-push out to side (and back some too): Head and shoulders move strongly _sideways_ away from the direction of the leg-push, and already _upward_ lifted by the back muscles. The _reactive_ forces from this combined move go down and sideways in the direction of the leg-push, so the upper body _adds_ to the force of the leg-push (by Newton's Third Law). Knee joint extends and pushes the ski out to the side with the quadriceps and rear-gluteus muscles. Arms finish pushing the poles backward. Off1 -- focus on lifting the upper body: Head and shoulders move further upward, and rotate back the other way to face the skiers overall line of forward travel. Land the ski with on well-bent knee. Knee straightens to lift the hips and the weight of the entire upper body. The back muscles continue the extension they started in Hang2 and further lift the weight of the shoulders and head (this lifting adds to forward-motion power by building potential energy which is later released in the pole-push). Off2 -- forward fall and leg side-push: Head and shoulders move strongly sideways and then crunch strongly down onto the hang-side, _before_ the hang-side ski lands. Hips stay mostly level. Reactive force from the sideways shoulder move gets added to the skate-push out to the side by the "off" leg. Reactive force from recovering the arms forward adds some force to the backward component of the skate-push. But reactive force from the downward fall of the shoulders _subtracts_ force from the skate-push, so it's better to delay that move to the last part of this phase and then do it quickly. Conclusion: This loop of the shoulders and head enables the upper body to deliver an amazing combination of sideways reactive force, downward reactive force, inertial force, and gravitational potential energy -- to add to the obvious direct pushing forces thru the skis and poles (and minimizes extra load on the primary skating and poling muscles). Comments: (1) My big flaws in my video clips that Sharon took of me skating V1 on Sunday are that I make all my side-to-side shoulder moves one phase too _early_, and start all my up-down shoulder moves half a phase too _late_. (2) The timing of the downward "crunch" by the abdominal and chest muscles came as a big surprise to me. Instead of directly helping push the pole tips into the snow, the crunch force is used to generate momentum in _advance_ in the Off2 phase, which is then applied thru the pole tips during the next Hang1 phase as an _inertial_ force. (3) It's best make the sideways moves of the head and shoulders during the phases when the skis already edged (Hang2 and Off2). Because if the ski is gliding nearly flat (like in much of Hang1 and Off1), then it doesn't to a good job of transmitting the sideways reactive forces to the snow. Note: In this respect skis on snow are completely different from rollerskis or inline skates on dry pavement, which easily transmit reactive side-forces when rolling flat -- or even when rolling on the "wrong" outside edge. That's how I had gotten my timing of my side-to-side shoulder moves all wrong: I figured them out practicing on pavement. (4) Some coaches see the Off1 phase as a waste to be minimized, because it looks like a loss of _momentum_. But actually it's a very valuable phase for delivering forward-motion _power_, but in a clever indirect way. And perhaps it is physically the most _efficient_ phase, since simple direct lifting is an excellent way to apply the big power of the big power to the main problem of hill-climbing: namely moving the weight of the body uphill against the force of gravity. So many new moves to play with -- I can hardly wait to get back on snow. How could the forecast for Wednesday be for rain? Ken |
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#2
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exploiting the head loop in V1 skate
Another move in the upper body sequence of the V1 skate of World Cup winners
is the raising of the hang-side shoulder at the start of the pole-push. Climbing the hills at Mt Van Ho last weekend, I found this to be my new key move for making it _easier_ to survive the ridiculous hills of Porter Mountain. Of course it's another plain violation of the New Skate "quiet upper body" religion. Seems like every time I find a new way to violate the New Skate in my V1 technique, the easier it gets for me to ski. My great memory from Saturday was _gliding_ up through the steepest part of East Mountain. Of course I was pushing too -- but with the extra power from that new raise + dip of my shoulders, it felt like miraculous floating upward -- at least compared with my previous expectations. (East Mountain is the hill that had to be modified for the 1980 Winter Olympics after the Soviet coach claimed that it was too hard). The biomechanical advantage of this raising of my hand-side shoulder (together with dipping of my off-side shoulder) is obvious and direct, not some tricky "reactive force" thing. When I "unwind" my pole-push from that tilted-shoulder start position, I engage new muscles in my chest and abdomen that are aimed more directly into my primary hang-side pole-push, and also support my off-side pole-push. I find this extra aid allows me to drive my hang-side pole _down_ in a whole new way, and my legs really appreciate the help. To make skating up a hill _easier_, I need to go beyond "core stability" to core _action_ -- use new core muscles for extra _propulsion_ power. To make skating up a hill easier, I need to go beyond just "naturally" turning from side to side -- find the muscles to _power_ the turning, enhance the timing and coordination to optimally _exploit_ the turning for additional power -- to take some load off my primary muscles. Ken |
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