what's here
goals
for Leg Recovery
physics
of adding Work from Recovery moves
simple
Normal-push
Double-push
more . . .
[ under construction ]
do not waste time
Stroke-cycle time is precious for Power and Speed in skating. Time
wasted during leg-recovery results in a reduction of rate of Power
output (in Watts) from every other muscle move -- because Power depends
on frequency, and time wasted in leg-recovery reduces turnover
frequency.
do no harm ... to Set-down and Pushing
Key thing is not hinder the big Extension push. An
important part of the Extension push is to "slice" or "carve" the foot
forward (using the knee-extension muscles).
You can't slice the foot forward if the foot does not
start backward. There's two ways to get the foot backward: Set it
down in a backward configuration already, or move it backward (after
setting it down not backward).
Either way, the implication is not to have
substantial forward speed of the foot at Set-down.
If your strategy is to move it backward after
Set-down, that will use up more of precious stroke-cycle time if the
muscles must first slow and stop the forward momentum of the leg before
starting the foot moving backward. Also the neuro-muscular control to
suddently switch from forward to backward could have inaccurate timing
or delays -- not what you want while your muscles are tired and you need
to focus attention on other aspects of your skating situation.
(Exception: If choosing to use a
backward-forward reactive-force strategy with the Pivot-Aim style of
Normal-push, then forward swing of the leg could be helpful.)
Knee out behind versus close: Therefore,
avoid the approach of holding the knee out a ways behind --
because the tendency will be to swing it forward into Set-down.
If you do send the foot out behind during Recovery,
start bringing it forward immediately, so its forward motion can be
slower just before Set-down.
Or simpler, just don't send the knee so far backward at
all during Recovery thru the air. Focus more on sideways motion. (Which
also fits with the Finish of the Extension Push being aimed more
sideways than backwards).
High versus Low: Recovering the leg higher, and
holding it higher, tends to lead to more speed into Set-down, because of
the assist from gravity. If you do bring the leg high in recovery,
start bringing it downward immediately, so its motion can be slower
just before Set-down.
Or simpler, just don't send the foot so high at all
during Recovery thru the air.
Foot versus Knee: Bending the knee during
recovery has two advantages: Relaxes the knee-extension muscles, and
prepares for a bent knee at Set-down. Bending the knee tends to bring
the foot backward and upward -- which seems to contradict the other
points in this section. But the foot has much less mass than the rest of
the leg, and it's easier for muscles to control the speed and direction
of the foot moving into Set-down.
add propulsive work
The motion of the recovering leg thru the air can add
propulsive Work (measured in Joules) -- which will add Power and speed
to skating.
Making this happen is tricky -- because often the Work
generated in one phase of a motion gets canceled out by another phase.
Critical success factors are: clever selection of the motion, and
careful timing synchronization.
see lots more detail under
physics of adding Work.
help Set-down and first pushing phase
help start Sweep-Out move
The
simple
Normal-push style of skating starts by pushing directly sideways
outward from underneath the hip, immediately after Set-down. If the leg
and foot are already moving sideways thru the air just before setting
down, they carry momentum into this initial phase. Also the
neuro-muscular control is simpler and more reliable if the move is
started before Set-down. Trying to start the move exactly at Set-down
might be subject to timing inaccuracies or delays in the neuro-muscular
control.
Bringing the foot a little further inward than
necessary in Recovery provides the space needed for this outward move
into Set-down.
help setting down inside + without pronation
Pointing the foot down or inward (by lateral rotation of the ankle
joint) in Recovery for Normal-push: I find it helps me then set
down the foot without ankle-pronation. Or if my strategy is to set down
the foot inside from underneath its hip, seems to help with that too.
Also makes my Normal-push recovery move more like my
Double-push recovery.
The motion of the recovering leg thru the air can add
propulsive Work (measured in Joules) -- which will add Power and speed
to skating.
Making this happen is tricky -- because often the Work
generated in one phase of a motion gets canceled out by another phase.
Critical success factors are: clever selection of the motion, and
careful timing synchronization.
Different kinds of skating must use a different kind of
recovery motion to succeed in adding propulsive Work:
-
simple Normal-push: from the sideways move of the
leg into Set-down.
-
Pivot-aim Normal-push: from the forward move of the leg
into Set-down.
-
Double-push: from the sideways move of the leg lifting
up and across to the inside.
For more on this kind of skating, see
Simple
outward aiming angle.
In Normal-push the move from Lift-up to Leg-Recovery cannot add net
positive propulsive Work, because both its starting and its stopping are
made with the pushing foot aimed at the same angle in the same
direction.
But in the "simple" style of Normal-push where the foot is
set down already aiming toward the outside, there is a way to add propulsive
Work (measured in Joules) from the sideways component of the move from
Recovery into Set-down.
The maximum amount of propulsive Work that can be added
to simple Normal-push is roughly equal to the kinetic energy of the mass
of the leg at the sideways
speed of the foot just after Set-down -- maybe a little more or less,
but not much more.
So there's no purpose in bringing the
foot and leg further inside toward the other leg than is sufficient to
give enough space to easily accelerate the foot + leg up to the sideways
speed they will have just after they are Set-down. The sideways speed
just after Set-down is determined mainly by: (a) the aiming angle of the foot
just after Set-down, (b) the turnover frequency, and (c) the skater's
overall forward motion speed.
At "cruising" speed in non-high-force situations,
typically the aiming angle is not very large away from straight forward,
so the sideways speed just after Set-down is not large -- so there's no
reason to bring the foot very far inside in its leg-recovery move.
In higher force situations like climbing up a steep
hill, the foot typically lands aiming and gliding more out to the side,
and the turnover frequency is typically higher, so the sideways speed
just after Set-down is higher. So it makes sense to bring the foot a
little farther toward the other side in leg-recovery, to provide enough
distance to easily accelerate it to a higher sideways speed going into
Set-down.
Note that the "farther toward the other side"
is measured relative to where this foot is going to land
on the ground -- not relative to wherever the other foot is already on
the ground. Since the feet are typically farther apart when climbing a
steep hill, it makes a difference how you measure it.
But what matters for the amount of added propulsive
Work the speed just before and after Set-down. So if you don't use the
extra sideways distance in leg-recovery to add more speed, then there's
no benefit. And if you can accelerate the mass of your foot + leg
quicker, than you can get by with a shorter sideways distance in
recovery. If taking the extra distance in leg-recovery slows down your
overall stroke-cycle turnover frequency, then it's likely a bad thing.
Quickness is more important than distance.
Pointing the toe down in the Leg-recovery move -- or
even pointing it inward toward the other side -- can add a little bit
more propulsive Work without slowing down stroke-cycle time. Because
then the move of pointing the toe back forward and outward going into
Set-down, moves a little more mass sideways, and uses different muscles
to do the work of accelerating it sideways.
But for Normal-push the benefit of this is minimal, because
it's usually easy to get to the maximum Work from the move into Set-down by
using other muscles. I still like to point the toe down because it seems to
help me with other aspects of my Set-down configuration, and because it
keeps me in practice to do it for Double-push.
Pivot-aim Single-push
See the
note about Set-down timing subtleties for the
Pivot-aim
style of Normal-push, and the
note about foreward-backward reactive force.
For Double-push, the move going into Set-down cannot
add propulsive Work, because the sideways speed of the foot just after
Set-down will be in the inward direction, so any move started
from Leg-Recovery toward the outside must stop its sideways
motion before Set-down -- so the stopping cancels any added propulsive
work from the starting. Then the sideways inward just after (and before)
Set-down is slightly negative for propulsive Work -- but it's
unavoidable it you want to get the large positive propulsive Work from
making that inward push.
Therefore the move from Leg-recovery into Set-down can
be a bit "lazy": its path and speed don't matter much -- provided
it does not slow overall stroke-cycle frequency, and that the foot and
leg are going into a strong inward-push at Set-down.
What does add propulsive Work in the leg-recovery move
for Double-push is (1) starting and accelerating the mass of the leg +
foot toward the other leg, away from the inward push being made by the
other leg that was just Set-down; and (2) decelerating and stopping that
Leg-recovery move while the other leg is making its outward push.
The amount of propulsive Work added is
determined by the recovering leg's maximum speed sideways toward the
other side during the Aim-switch. And that work is added to both
the inward-push and the outward-push.
Unlike simple Normal-push, there is no limit on how
much Work can be added in this way. The limit is how strong your muscles
are for quickly accelerating the leg and foot sideways through the air .
. . and in how good your timing is in having it hit maximum speed at the
moment of Aim-switch, instead of sometime before Aim-switch.
A possible problem (which I have not seen in video)
would be in starting and executing the leg-recovery move too early, so
its sideways acceleration is already finished while the other foot is
still aiming inward, so its speed is slower by the time the foot is
aiming outward.
Some skaters might
even have to learn to hold back the start of the leg-recovery move -- leave
the foot "hanging out there" for couple of momemts after Finishing its
main leg-push and lifting up off the ground.
Since the mass of the leg + foot, and the muscles used
to move them are both different from the mass and muscles used for the
torso-shoulder side-swing move, the timing of the leg-recovery move
might be different from the timing of the torso-swing move. (As if
Double-push were not already complicated.)
No simple "trigger" trick for timing this
move (unlike torso side-swing): Have to check it in
video.
Pointing the toe down in the Leg-recovery move -- or
even pointing it inward toward the other side -- can add a little bit
more propulsive Work, without slowing down stroke-cycle time. Because it
moves a little more mass sideways away from the inward push being made
by the other leg that was just Set-down, and uses different muscles to
do the Work of accelerating it sideways.
But once the other (pushing) foot is aiming outward, this
does not matter any more for propulsion in Double-push -- so can relax the
ankle-rotation muscles and allow the foot in the air to point more
naturally, and aim somewhat outward -- which helps prepare for an outward
path into Set-down.
see the
discussion of the
physics of adding propulsive Work from Recovery moves.
Especially for Normal-push (where the maximum propulsive
Work from Recovery is limited), it is important to observe the amount of
time spent in Recovery.
Simplest way is to count the number of video frames between
lifting up off the ground to setting down on the ground again.
Serious speedskaters can practice quickness of Recovery,
and measure their progress in development.
Can also count the number of frames for the entire
stroke-cycle, and see what is the percentage of Recovery.
The amount of propulsive work added from torso side-swing
and arm-swing moves is often higher if the foot is set down earlier
(if it is alreadly aiming toward the side, not straight forward).
Priority: B-
Shortly before Set-down, the leg and foot should be more
inward toward the other leg than they will be at Set-down.
For how far inward, see the
discussion of the physics
of adding propulsive Work. Usually it's not as far inward as the other
leg.
Note that the "how far inward" is measured
relative to where this foot is going to land on the ground
-- not relative to wherever the other foot is already on the ground. The
recovering foot moves toward the other foot, but for purposes of
analysis you do not measure it relative to the other foot.
Whatever else happens in between lifting the leg up off the
ground and getting to that inward position just before Set-down is not very
important for propulsive Work -- unless it wastes stroke-cycle time.
Moving the leg further inward sideways than necessary does
not add propulsive Work, but it might cost stroke-cycle time.
Note that sideways reactive-force moves (e.g. torso
side-swing and arm-swing) in Normal-push usually generate a larger amount of
propulsive Work if the foot is set down earlier, already aiming
outward.
Pointing the foot downward or inward
Usually irrelevant for propulsive Work in simple
Normal-push -- except it might add some in a high-turnover high-force
situation: like climbing up a steep hill, or sprinting.
But it can help for non-propulsive reasons -- see under
goals for Leg Recovery.
see the
discussion of the
physics of adding propulsive Work from Recovery moves.
There's nothing much important for propulsive Work for
simple Normal-push in the side view of the leg recovery.
Lots of speedskaters like to bend their knee -- perhaps it
helps relax the leg muscles between pushes.
There's no advantage to the leg going further backward than
necessary. What's important for propulsion is the side-to-side motion.
No reason why the knee cannot stay almost as far forward as
the other leg. Seems like keeping the leg closer forward fits better with
the Finish of its previous push being aimed more outward sideways than
backwards.
For possible disadvatages to bringing the leg farther
backward or upward see under goals for Leg
Recovery.
Key things to watch for:
See the
note about Set-down timing subtleties for the
Pivot-aim
style of Normal-push, and the
note about foreward-backward reactive force.
Since the physics of getting any propulsive work from
this style is completely different from the "simple" Normal-push, some
of the leg-recovery motions and video observations will likely be
different.
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