what's here
details of each phase
for double-push
technique, the "in-push"
phases ip0, ip1, ip3, and ipA are described on a separate page.
They replace Phase 0 of the normal-push stroking sequence given here.
see also
This is a detailed analysis of the sequence of moves for Leg-push motions
of "normal push" method of skating.
The additional "in-push" moves and phases
for the "double-push" skating technique used by expert inline skaters are on a
separate page.
The focus is on the effectiveness of various moves and timing
sequences for propulsion, not fun feelings. But of course the main
reason I choose to skate is because it feels magical and fun -- we say
more about connecting the moves to those goals on other pages.
The immediate concern is for skating with skis on snow, but there are
also notes for inline skating and ice skating, how the motions are
different for those different kinds of equipment and surfaces.
This sequence of phases is not the "right" way to skate. Rather it
offers a reasonable set of options, and analyzes the reasons for
choosing (or not) each one. Few skaters do all these moves, and I doubt
there is any skater who does all of them all the time. The main purpose
of this analysis is to expose skaters and skate instructors to more
choices -- more variety and more freedom.
Sources of these moves and timing sequence:
- analysis of the basic physics and biomechanics.
- videos of elite racers, analyzed with pause and
single-frame-advance.
- suggestions from other skaters and coaches.
- my own personal experimentation with different moves.
for lots more detail, see
separate page.
Here's some key findings:
-
Theme: Prepare to add reactive force to Set-down
phase, and perhaps currently add reactive side-force to the other
leg's push.
-
The parts of the leg are brought inward further toward the other side
(while in the air) than would be necessary to reach the landing
position of the set-down. This adds propulsive work in this phase
(for double-push stroking), or enables added propulsive work in the
next Set-down phase (for normal-push stroking).
-
There may be propulsive work from bringing parts of
the leg further backward (while in the air) than would be necessary
to reach the landing position of the set-down phase -- but only if
there are certain motion patterns in the push phases of the other
leg.
[ normal-push: ] If using simple obvious push with a
constant aim-angle throughout, there's little need to give attention to forward-backward leg motion in the Recovery and Set-down phases.
[ double-push: ] The
"lite"
style is better suited for extracting propulsion from
forward-backward moves in Recovery and Set-down phases. So if using the
"big"
style of double-push, less need to give attention to such forward-backward leg motions.
for lots more detail, see
separate page.
Here's some key findings:
-
Theme: Land foot early to start
pushing early, and in position to extract the most power out of
this leg's upcoming push.
-
"Overlap" Timing: Set down the next foot before the previous
leg-push finishes pushing: (a) to allow the mass of skater's body
to drop low without fear of falling over onto the ground; (b) to "catch"
the maximum percentage of reactive-side-force energy from the
previous leg-push and upper-body side-moves; (c) to support the last part of the push by
the other leg; and (d) to add power and minimize any "dead spot" gap
in the stroke-cycle, by starting this leg's push as early
as possible.
-
Prepare for effective range-of-motion in
Side-of-leg-Out
phase of main-push:
[ ski: ] Land the ski with
the minimum inward tilt needed to transmit force through the inside
edge -- or possibly sometimes even a bit on the outside edge. Set down closer toward underneath the pushing hip,
with knee pointed out, and with
as little ankle-pronation as possible.
[ skate
normal-push: ] Land the skate on outside edge further inside
than its hip, with the knee pointed outward, and with the ankle supinated.
-
Prepare for effective aiming of push-force and
range-of-motion in
Extension phase of main-push, by flexing the ankle strongly
forward, so the ankle joint is way back behind the knee joint.
-
Pelvis + hips do not face with aim of next
ski or skate at set-down (which is different from shoulders).
Optimal is to start with pelvis and hips facing somewhat toward the
opposite side, so during the leg-push the non-pushing hip moves
forward ("forward-abdomen-rotation" move). Then the pelvis + hips
will have turned to face with aim of the skate or ski at the end
of the leg-push. (Also, the most propulsively effective positions
and rotations of the torso + shoulders are often opposite to
those of the pelvis + hips).
-
The set-down move can do a little actual propulsive
work in itself -- not just preparation for work in other phases.
for lots more detail, see
separate page.
Here's some key findings:
-
Theme: Catch side-weight-shift energy
from previous phases and transmit it into current push-force through the foot.
Start pushing already with Side-of-leg-Out moves. Find a trick to
get through low-power phase 1b quicker.
-
Maximum transmission of side-weight-shift energy
into the foot: No absorption or collapse.
Effective transmission uses the same
Side-of-leg-Out muscles (and Forward-abdomen-rotation and Torso-swing
muscles), but in "eccentric" and/or "isometric" modes.
One absorption "trap" is
to allow the hip to go outward relative to the knee, instead of
stabilizing the hip-knee configuration with the
lateral-hip-abduction muscles.
-
The time just after the foot lands does not have to
be "passive glide". The leg can already start doing actual propulsive
work by using Side-of-leg-Out moves.
-
Ankle-flexion move (if not already complete in
Set-down phase 0) prepares for Extension moves in future phases -- by
moving the ankle joint way back behind the knee, which "aims" the knee-extension push so
it can help the Extension push out toward the side. It also adds range-of-motion to the
ankle-extension push.
-
Hold back on leg Extension moves.
In this phase they are "aimed" mainly to raise
the hip upward (and this vertical potential energy is inefficiently
converted into later propulsion except for a skier using a pole-push).
The Extension moves will be more effectively "aimed" for propulsion
starting in phase 2 and more so in phase 3, when the leg-lean angle is
larger. (Then the hip will get raised up plenty.)
[ inline + ice-rocker-blade ] Skaters can get
to a phase 2 leg-configuration quicker by aiming the skate out further
to the side during phase 1b, then pivoting it during phase 2 to aim move
forward during phase 3.
(formerly "Central push phase")
Blend of some Side-of-leg-Out moves with some Extension push moves.
for lots more detail, see
separate page.
Here's some key findings:
-
When in doubt, hold back on the starting and/or the
magnitude of the Extension push force -- since there's a limit to
its range-of-motion, and the more of it that can be saved for later,
the larger its contribution to propulsive power.
-
Postpone the ankle-extension move as long as
possible -- into Phase 3b. Transmission of push-force is more
effective through the heel of the foot. And the ankle-extension move
is better "aimed" for propulsion after the leg is close to straight.
-
Hold the Upper Body quiet. Wait for the better
moment. Any upper body move which could be helpful in this phase
could be done with bigger contribution to propulsive power either
earlier in phase 1 or later in phase 3.
for lots more detail, see
separate page.
Here's some key findings:
-
Theme: Finish the leg Extension moves with
maximum force -- and quickly. In phase 3b, start the
Upper-Body-swing moves late with aggressive quickness, then
try to set down the next foot early before this leg-push
ends.
-
Knee-extension move (using the big "quadriceps"
muscle) is often ignored, but it is critical for effective
propulsion. Perhaps it gets overlooked, because it requires a
(non-intuitive) "slicing" the foot forward
relative to the hip -- and because it has the (also non-intuitive) ankle-flexion as
its
prerequisite.
The hip-extension and knee-extension moves
work together in skating propulsion. Either one used alone is
"aligned" ineffectively, but working together they can offset each
other's misalignments, and produce a strong push out through the foot to
the ground.
Actually it is not effective to go to "true"
full extension of the length of the leg, because some of the muscle moves needed to achieve
maximum length (e.g. ankle-supination, lateral-hip-rotation) if used in
the Phase 3 configuration are
either not propulsive or have bad side-effects for future phases.
-
Postpone the ankle-extension move as long as
possible. Transmission of push-force is more effective through the
heel of the foot. And the ankle-extension move is better "aimed" for
propulsion after the leg is close to straight.
-
Ankle-extension move can also add a force to
inline skates with the usual kind of wheelframe design (i.e.,
non-klap). (On an inline skate, perhaps this ankle-extension might be combined with a little
outward-ankle-rotation move.)
-
Hold back on starting the Upper-Body-swing moves,
and then start them with maximum quickness. The upper body parts
being moved sideways should reach their maximum sideways velocity
just as the next foot is landing on the ground.
Most skaters start the Upper-Body-swing moves
much too early for maximum reactive-side-force contribution to
propulsion.
Checkpoint: In a front view, try to have the
center of each moving upper body part not cross the imaginary vertical
line through center of the hips until after the other foot has been set
down.
[ double-push ] - Timing is different for
double-push skating. The start of Upper-Body-swing moves should be
postponed until the last phase of the in-push, just before the
Aim-switch phase A.
more findings for this phase:
-
Vertical hip motion: If the various sets of muscle
moves (with no poling) are prepared and timed and aligned for
maximum propulsive power, the pushing hip should slowly rise during
phase 2 and reach its maximum height off the ground near the
beginning of phase 3, then drop first slowly and soon rapidly.
(unless poling equipment and moves are being
used) It is counter-productive to cause (or allow) the hips to
rise earlier. While it is true that the rising of the hips (and
connected upper body parts) adds vertical potential energy. But this
vertical energy is not very well-aligned with the skate-push for
propulsion. So it's more effective to save the range-of-motion of
leg-extension for direct pushing out through the foot later, than
it is to use leg-extension indirectly to raise the mass of the
upper body.
[In "classic" (non-skating) cross-country
skiing at higher speeds, there are basic limitations of alignment and
quickness for using some leg extension moves for propulsion. In that
situation it can make sense to use leg extension moves indirectly,
to raise the mass of the upper body, then use that to add power to
poling -- because the alternatives are worse.]
The obvious move sequence is to prepare by
allowing gravity to slowly lower the mass of the upper torso and
shoulders and head during phase 1 and phase 2 and much of phase 3. Then
start using the back muscles to raise the mass of the upper torso
and shoulders and head, just before the end of this phase. Timing must
be accurate, so the maximum vertical velocity comes as the foot is
lifting up off ground, and the maximum height of the shoulders is not
reached until after weight has been fully transferred to the
other foot (whose leg-lean angle is close to 0°).
But . . .
Side-weight-shift reactive-force ought
to get much higher priority than up-down reactive force, because:
(a) it delivers propulsive work on both
acceleration and deceleration segments of its moves;
(b) side-force is better aligned for
skating-propulsion, very much better in phase 1 and phase 2;
(c) the back muscles have other important
things to do in most skating, like support the weight of the upper torso
and head while bent forward into a low aerodynamic position.
The obvious move sequence is to add a forward
component to the sideways arm-swing. The problem is how to avoid having
the negative of deceleration cancel out the positive of acceleration.
The solution is timing: Make the acceleration forward while the
aim-angle of the foot is large (out toward the side), then allow the
deceleration of the forward move while the aim-angle is small (nearly
straight forward). Recover to start the next foward move by starting the
acceleration backward while the aim-angle is small, and allow the
deceleration of the backward move while the aim-angle is large.
Double-Push stroking could support this
timing, with the acceleration forward during the end of phase 3 of
main-push, and deceleration of forward move during phase ip1 of in-push.
Then acceleration of arm-recovery move backward during Aim-switch phase
A, and deceleration of backward move during phase 3 of next main-push.
To do it, first prepare by moving the arm
backward slowly during phase 1 and phase 2 and much of phase 3, but keep
hold it there out toward the side of this leg-push. Then start the
arm-swing just before the end of this phase. Timing must be accurate, so
the maximum forward vertical velocity comes as this foot is lifting up
off ground, and the maximum forward position of the arms is not reached
until after weight has been fully transferred to the other foot
(whose aiming-angle is close to straight forward).
But . . .
Side-weight-shift reactive-force ought
to get much higher priority than forward-backward reactive force,
because:
(a) side-weight-shift delivers propulsive work
on both acceleration and deceleration segments of the moves;
(b) The situation when arm-swing is going to
be important is when going slow, like climbing up a hill -- but in that
situation it is also important to set down the next foot with aim-angle
more out toward the side, so it can start delivering a strong
Side-of-leg-Out contribution immediately.
For the forward component of arm-swing to be
overall helpful, need a situation slow enough to benefit from arm-swing,
but not so slow that there's no "slack" in the stroke-cycle available
for set-down with aim-angle close to straight ahead.
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