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How to coordinate the timing of multiple dimensions of upper body moves:
The three dimensions are:
-
side-swing
-
up-down
-
forward-backward
[ more to be added ]
For the arms and for the torso, controlling up-down
motion is somewhat independent from side-swing motion. Though it's
simpler to make a single straight path of the hands from the
start to the finish of an arm-swing move. And it's easier to move
up-left to down-right than it is to move up-left to up-right. Also
easier to move middle-left to middle-right than move down-left to
down-right.
But producing effective propulsive work is
never "easy", so we can use extra muscle moves to change the direction
of our hands in the midst of the arm-swing: e.g. from down-left move the
hands upward to mid-level across the center, then turn the hands
downward to finish down-right. In skating the optimal timing is often
not "simple", but it's an interesting challenge to learn to coordinate a
more complex rhythm.
So for arm moves and torso+shoulder moves, there is
lots of flexibility to coordinate timing to obtain simultaneously a
substantial percentage of the propulsive work available from both the
up-down and side-swing dimensions.
simple Normal-push stroking
Since forward-backward upper-body moves are
self-cancelling for simple "straight-stroke-path" normal-push, we get
this phase-sequence of upper body moves:
-
phase 1: Slow and stop the torso + shoulders
and the arms + hands -- in a position high and out toward the side
of the current leg-push.
-
later in phase 1 or early in phase 2: Start
lowering the shoulders, and the arms even more so -- but keep them
out toward the same side -- try to avoid letting the hands drift
back into the center.
-
early in phase 3: Stop the shoulders and the
arms in a position low and out toward the side of the pushing leg.
Forward-backward components of arm+hand motion are
irrelevant for this kind of stroking -- allow whatever seems to make the
other moves easier -- when in doubt use less forward-backward.
(The
"angle-switch" or "hop" variations of normal-push could
also get more
complicated.)
Double-push stroking with nearly horizontal torso
When the hip-shoulder line is somewhere near horizontal
(for aerodynamics), forward-backward shoulder moves are mostly
determined by the timing of the side-swing moves (because the side-swing
moves are simpler to control and have a bigger impact on propulsion).
(Double-push in a somewhat erect position gets more complicated
for torso + shoulder moves -- see under
Timing
Forward-Backward versus Side-Swing moves)
So we get this optimal phase-sequence for the torso +
shoulder moves:
-
phase 3 of previous leg-push: Start the torso
+ shoulders moving upward -- while keeping them out toward the side
of this previous leg-push. Try to avoid starting the next side-swing
move too early, and try to limit the "drift" in toward the center.
-
phase ip1 + ip2: Stop the upward move of shoulders,
and start the shoulders moving across toward the side of the new
pushing leg.
-
phase 1: Slow and stop the side-swing of the
shoulders, way out toward the side of the pushing leg. Start
moving the shoulders downward.
-
phase 2: Continue lowering shoulders, while keeping
them out toward the side of the current leg.
-
early in phase 3: Stop the shoulders in a position low and out toward the side of the pushing leg.
So the shoulders make both their upward and downward
moves mostly while facing toward the side of the currently pushing leg
-- not while facing ahead forward.
Arm swing moves
For the arms and hands we have lots of freedom to move
in various combinations and sequences of all or some of the three
dimensions. Though it's simpler to make a single straight path of
the hands from the start to the finish of an arm-swing move. And it's
easier to move back-down-left to forward-up-right than it is to move
forward-up-left to forward-up-right.
But producing effective propulsive work is
never "easy", so we can use extra muscle moves to change the direction
of our hands in the midst of the arm-swing: e.g. from down-left move the
hands upward to mid-level across the center, then turn the hands
downward to finish down-right. In skating the optimal timing is often
not "simple", but it's an interesting challenge to learn to coordinate a
more complex rhythm.
So for arm and hand moves, there is lots of flexibility
to coordinate timing to obtain simultaneously a substantial percentage
of the propulsive work available from both the forward-backward and
up-down dimensions.
For most skating phases:
-
Positive for propulsive work: Stopping
downward or backward, and Starting upward or forward tends be
positive.
-
Negative for propulsive work: Stopping upward
or forward, and Starting downward or backward tends be negative.
Therefore, if forward-backward upper body moves can add
non-self-cancelling propulsive work, it tends to optimal to:
Double-push arm-swing
The truly optimal coordination of timing of all three
dimensions of arm-swing for double-push not that hard to describe
theoretically, but overwhelmingly complicated to learn and to control --
since each of the three dimensions has a completely different timing
sequence.
Here's three levels of simplification for double-push
arm-swing:
-
Figure out the best timing for moving the arms
forward (and backward), and use the same timing for moving the arms
upward (and downward). This gets only half the benefit from up-down,
but that's something.
-
Minimize up-down motion of arms, just focus on
side-swing and forward-backward moves of arms.
-
Ignore both forward-backward and up-down motion
components of arms: Just focus on good timing of side-swing, and
whatever other motion components seem to go with that.
Torso + Shoulder moves
There's less freedom in coordinating forward-backward
and upward-downward for torso + shoulder moves: because in a typical
body-configuration for skating,
-
If the torso is held aimed facing forward, then
moving the shoulders forward tends to require some downward (and
backward tends to require some upward).
-
If the shoulders are held at a constant level and
are currently aimed toward one side, then the only way to bring them
forward is to also move them sideways in toward the center.
-
If the shoulders are held at a constant level and
are currently aimed forward, then the only way to send them backward
is to also move them sideways out toward one side.
Unfortunately the propulsive impact of a downward
upper-body move tends to be opposite to a forward move, and upward has
opposite propulsive impact to backward.
So what's good for the timing of up-down moves tends to
bad for the timing of forward-backward moves.
In simple "straight-stroke-path" normal-push,
forward-backward upper-body moves are a wash, and there is slight
benefit to blending some well-timed up-down torso-shoulder movement with
the side-swing.
For double-push it's more complicated because
forward-backward can have an impact on propulsive work. And in the
three-dimensional geometry of skating, the forward-backward impact tends
be larger than upward-downward -- so could be better to prefer to give
forward-backward considerations influence on the timing-coordination of
moves.
But usually the impact from side-swing tends to be even
larger (and simpler to manage), so it should dominate both the up-down
and forward-backward dimensions.
For most of us non-elite speedskaters, likely
it's better to just not worry about forward-backward and upward-downward
moves in our double-push, and instead focus on getting good timing with
our side-swing moves.
The optimal timing of Forward-Backward moves has an
interesting relationship to the Side-swing moves.
Double-push stroking
Optimal coordination of timing is:
-
Backward -- The starting and stopping of the
Backward move should be roughly simultaneous with the starting and
stopping of the Side-swing move.
-
Forward -- The starting and stopping of the Forward
move should optimally be performed in between the Side-swing
move in one direction and the next Side-swing in the other
direction, while the Side-swing is being "held back".
Arm + Hand moves
This implies a rather non-intuitive
arm-swing sequence:
-
In the later part of the leg's in-push, the arms
start to swing sideways toward the current pushing leg -- and
also backward. (phase ip2 into phase A)
-
Stop the arms way out there on the side (and back), in the earlier part of the leg's main-push. (phase 1)
-
Keep the arms out there to the side and back during phase 2 -- try to prevent them from drifting in toward
the center, and hold back against the temptation to start the next
arm-swing move too early.
-
Arms start moving forward during the
later part of the leg's main-push, but remain over on the same side
as much as possible. (phase 3, perhaps simultaneous with phase ip0
of the next leg)
-
Arms finish moving forward as much as possible
during the early part of the next leg's in-push. (phase ip1 of the
next leg).
Torso + Shoulder moves
Side-swing moves of the torso + shoulder inevitably
produce some forward-backward component.
If the shoulders are very low in an aerodynamic
position, so that the line from hips through the shoulders is nearly
horizontal, then forward-backward is mostly determined by the side-swing
motion and position. Which implies that the shoulders move forward
during the first half of the side-swing, then backward during the
second-half.
If the shoulders are somewhat erect, at a significant
angle above horizontal, then the skater can affect the forward-backward
component by using up-down moves of the shoulders.
-
Increase forward-backward: If the shoulders move
down during the first half of the side-swing and/or up during the
second half, that increases the forward-backward component.
-
Decrease forward-backward: If the shoulders move up
during the first half of the side-swing and/or down during the
second half, that increases the forward-backward component.
Unfortunately the propulsive impact of a
downward upper-body move tends to be opposite to a forward move, and
upward has opposite propulsive impact to backward. But a higher
percentage forward-backward impact tends to get transmitted -- see
discussion under
Timing
Forward-Backward versus
Up-Down moves.
torso-shoulder moves for nearly horizontal torso
If the hip-shoulder line is something close to horizontal (for
aerodynamics), then up-down moves will have virtually no impact on
forward-backward component of torso + shoulder motion. So the main way
to change forward-backward component is with side-swing moves. But the
propulsive benefit from reactive side-force is bigger and simpler to
control, so it makes sense to let the side-swing considerations drive
the timing.
So in the case of skating with a nearly horizontal torso, there's no
point in worrying about forward-backward motion of shoulders. Just let
that be whatever is required by the side-swing moves -- instead try to
coordinate up-down torso moves, as in
Timing up-down versus
side-swing moves.
torso-shoulder moves for somewhat erect torso
If the shoulders are somewhat erect (rather than nearly
horizontal with the hips for aerodynamics), this sequence below seems to
be the best way to exploit forward-backward motion.
-
phase ip2 into phase A: In the later part of
leg's in-push, the shoulders start to swing sideways and backward
(and perhaps upward).
-
phase 1: Shoulders stop out there toward the
side (and back) during the earlier part of the leg's main-push.
-
phase 2: Shoulders are kept there out toward the
side of the current pushing leg, held back from drifting in toward
the center, or starting the next side-swing move too early.
-
phase 3: (if the hip-shoulder line
is not close to horizontal) Shoulders start to duck forward during the leg's main-push.
If the hip-shoulder line has some significant
angle above horizontal, ducking the shoulders also moves the forward.
The forward-backward reactive force from that move propulsive force.
During this phase there is high transmission of forward force into
effective propulsion (because the foot is aimed more out toward the side
than during the in-push or aim-switch).
Unfortunately the downward motion has a
negative impact on propulsive force, but up-down forces are not usually
transmitted as well as forward-backward forces, so there is often a net
gain from this move. But if the hip-shoulder line is near horizontal,
then the downward component will be much larger than the forward
component, so even with less transmission of downward, the net impact
will be negative.
If the start of the next side-swing is held
back until the in-push of the next leg, then the only way to move the
shoulders forward is to duck them down. If the
It's hard to avoid also starting some
sideways-move toward the other side. If
Elite racer videos
Some elite racers in their videos of double-push
stroking show this timing:
Since they start their side-swing (earlier
than optimal for exploiting side-force) during phase 3 of the leg's
main-push, this might (if the hip-shoulder line is not close horizontal
for aerodynamics) more propulsive force during a high
transmission of forward-force phase.
Since this comes during the in-push and
aim-switch phases, it subtracts more propulsive force during a low
transmission of forward-force phase.
Since the positive comes during a higher-transmission
phase than the negative, there is a net positive contribution of
propulsive work -- provided that the hip-shoulder line is not close
horizontal for aerodynamics.
On the other hand, since the associated vertical
component of torso-shoulder motion has an opposite impact on propulsion,
the overall gain from this is reduced.
But I think the bigger drawback is the less-effective
timing for the side-swing.
Normal-push with angle-switch or hop
Optimal coordination of timing is:
-
Forward move starts together with Side-swing move.
-
Forward move stops while Side-swing move is near
maximum velocity.
-
Backward move starts before Side-swing move
finishes.
This timing is possible to execute, but not the
coordination is surely not easy to learn or control.
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