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This is one phase in a detailed analysis of the sequence of moves for Leg-push motions
of "normal push" method of skating. For more context and
an overview of all the phases of the sequence, see
the summary of normal-push phases.
There is an alternate set of moves for this phase, often used by
ski-skaters -- see below.
-
Theme: Transmit side-weight-shift energy
from previous phases into current push-force through the foot.
Vertically raise the mass of the hips and upper body, to build
"potential" energy which will add to push-force in future phases.
Just after Set-down with the foot underneath the hip is the most
effective configuration for this lifting.
-
The time just after the foot lands underneath the
hip does not have to
be "passive glide". The leg can already be doing actual propulsive
work using moves describe here (also by starting some Phase 2 moves
early, especially transverse-hip-abduction).
-
Maximum transmission of side-weight-shift energy
into the foot: No absorption or collapse. 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.
-
Key move for raising the upper body is
knee-extension. These strong muscles are at a more effective angle
in this phase than in Phase 3.
-
Ankle-flexion move is also effective for raising
the upper body in this phase, and helps to bring the hips forward.
??
This phase goes from the landing of the foot on
the ground until (roughly) the completion of the "non-extension"
side-push moves (tranverse-hip-abduction, inward-hip-leg-rotation, ankle-pronation)
and (roughly) the start of the hip-extension move. But there is likely
significant overlap between phase 1 and phase 2, so perhaps it's more a
shift in focus between the two, rather than some well-defined "trigger".
The themes of this phase are:
-
Transmit the sideways-directed kinetic energy from
the previous leg-push.
-
Initiate pushing sideways (and partly backward) from
underneath (or almost underneath) the hip of the pushing leg (which
starts roughtly vertical). This push is "contractive" in that three out
of four of the moves have the effect of shortening the distance
between the foot and the hip. (This is the opposite of phase 3, where
the main goal is the lengthening of the distance between foot and hip.)
-
Put the leg joints into a more effective configuration
for phase 3 (and perhaps for phase 2).
?? [ to be added ]
[ physics and biomechanics parameters that drive the
amount of added propulsion work -- and the additional time it takes to
perform that work. ]
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overview of phases | R 0
1 2 3 | d-p
phases | more Leg
??
for forward propulsion:
??
and perhaps initiation of
for transmission:
- hip abduction -- valuable for "isometric" static transmission of
sideways kinetic energy from previous leg-push, even if not yet used
for active propulsion work:
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static transmission + support
No absorption by allowing the pushing hip to
go outward. The hip abductor muscles must "stabilize" the hip -- fight
the momentum of the pelvis and butt toward the next pushing side.
(Though the torso and shoulders can continue moving sideways a little
longer -- their timing is different, because they do not have a
transmission stability role.)
Even if the next foot is not visible pushing
yet, just having it on the ground and trying to hold its position
relative to the other foot is already adding force to Phase 3 of the
other foot's push. The force needed to "try to hold" the next foot (net
of some across-the-body transmission losses) is added to the pushing
force through the other foot.
early non-extension push
- Push out toward the side with the lateral-hip-abduction move.
These hip-abduction muscles are not large, but every little
bit helps -- to take load off the obvious big leg muscles.
Even if they do not have the strength to
actively push the hips thru any visible range of motion, at least the
hip abductors should be developed enough to "isometrically" stabilize
the side-weight-shift of the hips at the right time, and fight to
prevent the hips - pelvis - butt from moving any further toward the next
pushing side. They can try to hold the hip stable for
transmitting the side-weight-shift force.
Or if the other leg is still pushing into the
surface, and there is overlap of the final phase of the previous
leg-push with this initial phase of the next leg-push, then holding this
hip stable can provide a "fixed point" for the previous leg to push
against -- which adds to the effective force transmitted to the
snow.
The endurance and strength of the
hip-abduction muscles can be developed with specific training exercises.
Typically human muscles can apply more force when holding stable
("isometric") than when making an active push motion. And more force
when actively pushing slowly than when pushing faster. So even a small
muscle thought to be weak can play a key role in the chain of
transmission of big force and power, even if it shows no discernable
motion.
"pronating" = bending the ankle joint sideways
toward the inside of the knee-heel line.
But pronating adds work to propulsion only if
it is performed by active pulling by the ankle-pronator muscles
-- not just allowing the ankle joint to collapse downward.
[ inline: In "double push" technique,
supinating the ankle can add propulsion to the first (inward) push of
the stroke. ]
(If there is a leg-passive glide phase to
focus on pole-push, the start of this move might be delayed to Phase
1b.)
Bending to too large an angle of pronation
results in more negative work than positive -- because pronation also shortens the
overall leg-length. So need to stay within an angle small enough so that
the side-and-back push component is larger and the impact of the
component from shortening is smaller. Starting the pronation move at an
earlier Phase when the overall leg is more vertical helps keep the
negative component from shortening smaller. Then in later phases
supinate the ankle to get the benefit of full leg extension.
Though often criticized by instructors,
pronation is not all bad. It is bad as a position in Phase 0
(over-edging) and in Phase 3 (lazy collapse) -- which is what
instructors see reducing leg extension and power in many skaters. But an
ankle-pronation move is beneficial for power in Phase 1 and perhaps
Phase 2, provided the skater uses actual muscle-power to do it (instead
of lazy collapse) and remembers to re-straighten using the
ankle-supinator muscle for full extension in Phase 3.
(Setting down with the ankle in a somewhat
supinated position would enable a larger positive-propulsion
range-of-motion for the ankle-pronator muscles -- but for ski-skating on
snow that's not usually going to fit with the need to push through the
inside edge. So usually the best that ski-skaters can work on is trying
minimize the pronation at set-down.)
[ inline: In normal-push stroking,
there can be benefit to setting down with the ankle in a supinated
position -- if you have very well-trained ankle-pronator muscles to
exploit it. With "double push" technique, could set down with ankle
vertically straight in line or pronated slightly, then the
ankle-supinator muscles can help add propulsive work to the first
(inward) push, so then the ankle joint is already in a supinated
position at the start of the second (outward) push, and the
ankle-pronator muscles have more range-of-motion available to add
propulsive work to the outward push. ]
Note: This is remarkable, that both the original
move (ankle-pronation in Phase 1) and its reversal
(ankle-supination in Phase 3) can add positive propulsive work to the same
overall leg-push on the same side. The explanation is that each is timed
correctly with the vertical-angle position of the overall pushing leg.
At set-down the leg is roughly vertical, so shortening in the line of
the leg has only a small component of negative impact on forward-push or
side-push, mostly just reduces the compression of snow underneath the
ski base -- while the sideways component of the ankle-pronation move has
full impact on side-push across the ground surface. At later phases of the
leg-push the foot has moved out toward the side and back, so the overall
leg is aimed out the side and back, so lengthening of the leg by the
ankle-supination move then has a major component of impact on side-push
and forward-push -- while the sideways component of that move is aimed
only for a small negative impact, much of it just helps drive the edge
of the ski more down into the snow.
This move rotates the hips and pelvis about
the vertical axis -- so the hip joint of the next-pushing leg comes
forward -- and the hips and pelvis turn away from facing toward the
next-pushing side, and turn to face toward the current leg-push side.
This has several interesting helpful results:
- - uses muscles in the abdomen and
lower back (likely including the "obliques") to apply forward-propulsion
work by moving the mass of the next-pushing leg and hip and side of the
torso forward against air resistance (also gravity if going up a hill).
- - advances the next foot forward, but
without "stepping" it forward. The problem with "stepping" the foot
forward is that its hip joint gets left behind, which then requires the
hip-extensor muscles to operate in a less favorable segment of their
range-of-motion in the next leg-push. Instead the forward-hip-rotation
move advances the hip and foot together.
- - might help remind the hip abductor
muscles to do their pushing.
If there is a leg-passive glide phase to focus
on pole-push, the start of this move might be delayed to Phase 1b.
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overview of phases | R 0
1 2 3 | d-p
phases | more Leg
to sensitize to feeling how to push with the three
non-extension side-push moves:
-
two-leg parallel non-extension forward slalom:
Feet shoulder-width apart, big knee bend so hips are low like at
set-down. Keep feet parallel at times, push first with both legs
aimed diagonanally toward the left side (left foot on inside edge,
right foot on outside edge), then push with both legs aimed
diagonanally toward the right side (left foot on outside edge, right
foot on inside edge), and repeat several times. Keep feet parallel
to each other at all times, same width apart at all times (no
"sculling" of one toward or away from the other).
Focus on using only transverse-hip-abduction,
inward-hip-leg-rotation, and ankle-pronation to push outward with the
foot on inside edge. At the same time "mirror" those moves with the
other leg on its outside edge so it stays parallel -- so it will be
doing the opposites to the three inside-edge moves:
transverse-hip-adduction, outward-hip-leg-rotation, and
ankle-supination. The main role of the outside-edge foot is to make the
balance easy, but training these three outside-edge moves will also help
propulsion if ever use double-push technique.
No vertical motion of the hips. No "carving"
or slicing forward with the knee-extension muscles. Try to keep upper
body quiet and facing forward, no arm-swing.
For each of the three moves: (a) try to feel
range-of-motion, play with maximum starting position, play with maximum
finishing position; (b) feel the force and push transmitted into and
through the foot by the move, more than "going through the motion", try
to actively push at the start, and actively push through the finish; (c)
feel the timing of which segments of the leg-stroke are most effective
for pushing, and which are better left as a quiet transition to or from
the other side; (d) feel the "mirroring", notice how the maximum finish
toward one side puts the knee and ankle into position already for
maximum start toward the other side.
-
test of propulsion: climb up a gentle hill
using only two-leg parallel forward slalom.
-
single-leg non-extension slalom (with
toe-ride-balancer on inlines). Same moves as two-leg parallel
non-extension slalom, but with only one leg doing all the pushes
toward both sides. With inline skates, the other leg trails behind
only for balance, with only its toe-wheel down. Hip and upper body
stays quiet, no hip-extension permitted, and try to avoid
knee-extension forward-slice.
At first, can get moving forward using normal
skating, and just "go through the motions" of this exercise without
worrying about pushing -- just to get comfortable with the balance of
changing the aim and tilt directions while gliding on a single leg. Once
comfortable with the balance, again get moving forward using normal
skating, then use the moves of this exercise to try to maintain forward
speed, or at least see how far can keep going before come to a stop or
lose balance.
The next level of difficulty is to take away
the support of the trailing toe-wheel skate.
This exercise is also excellent training for
extracting maximum propulsion from the in-push phase ip1 of
double-push technique.
Final exam: single-leg non-extension
slalom up a gentle hill.
?? intro
alternate sequence
??
Phase Ski 1a = land w isometric hip-abduction and isometric
inward-hip-leg-rotation, to transmit side force from previous phase.
Phase Ski 1b = (optional) passive glide
Phase Ski 1c = inward-knee-roll and initiate ankle-pronation
Phase Ski 1d = ankle-flexion -- not in phase 2 because it's a
contractive move.
includes
??
??
see below under knee-drive move.
??
Sometimes it's desirable to have a phase with
virtually no leg-push work. If so, this is a good place in the
sequence for it.
Reasons for a leg-passive glide phase:
details + hints
Edge the ski a little during ski phase 1(a), then
fully flatten it for this leg-passive-glide phase, then back on some
edge for ski phase 1(c) or Phase 2 and beyond.
It's very hard to tell the difference between
Phase 1a and leg-passive glide just from analyzing a video -- instead
for reliable detection would likely need to put force sensors into the
skate or the ski
binding.
??
This move is used mainly by ski-skaters, not expert ice
or inline speedskaters. Question:
Why the
difference?
muscle moves
for forward propulsion:
prerequisite configuration:
- inward-knee-roll = inward-hip-leg-rotation combined with
tranverse-hip-adduction (or at least combined with lack of
hip-abduction support).
details + hints
- Ankle flexes forward deeply -- which moves the hip joint forward
so it is in front of the ankle joint.
The knee joint might extend slightly, but the
key thing is just to not let it collapse and absorb at all -- for full
transmission of other forces.
And delay most of the main leg-extension push thru the knee joint (by
the quadriceps muscles) and hip joint (by the gluteus maximus
muscles) until after the knee and ankle joints are in best biomechanical
geometry relative to the hip joint.
This an ankle-flexing move, not just a
flexed-ankle position. Having the ankle flexed foreward is generally a
good position for skating. But the point now is to flex the ankle
foreward even more -- more flex than could be sustained generally
through most of the leg-push. Maximum ankle-flex at the moment of the
big payoff -- just in time for the main leg-push.
This move requires using muscle power -- the
shin muscle (on the front of the lower leg). Lots of skaters do not have
much endurance and strength in their shin muscles.
[ ski + klap-skate: Keep the heel down. It's easier to drive the
knee down if the heel is allowed to come up off the ski, but it's too
early for that in this phase. The heel needs to stay down in the ski now
-- to be in position for maximum transmission of the main leg-extension
force in Phase 2. ]
For some reason me and lots of people find
that thinking directly about ankle flex doesn't engage the specific
muscles enough. I find it's valuable to think of it as a "knee-drive" move: driving the knee
down and forward toward the ground --
see more below.
If the ankle is flexed straight in the
direction of the aim-angle of the skate or ski, then the shin muscle is only helping
achieve a helpful biomechanical alignment for Phase 2. But there's also
a way to use the shin muscle to apply forward-propulsion work --
see below.
This "inward knee roll" move pushes the
foot a
little ways out and back, and the upper body a little in and forward. So
it adds to forward-propulsion power. Not much, but every little bit
helps -- to take load off the obvious big leg muscles.
(If there is a leg-passive glide phase to
focus on pole-push, the start of this move might be delayed to Phase
1b.)
The trap is that the "natural" way to
do this move is to allow the pushing hip to move outward at same time
the knee moves inward -- in which case the side-force benefit of the
inward knee move is mostly lost. The inward-knee-rotator muscles must work
together simultaneous with support of the hip-abductor muscles.
Video checkpoint: In front view, the pushing
hip should be vertically above the knee at set-down. The hip should
remain vertically above the knee during Phase 1. In elite-racer skating,
the shoulder normally moves outside the knee and hip during Phase 1, but
the hip does not move outside the knee.
This move also configures the leg for
propulsive moves in later Phases by other muscles:
(a) if the knee is inside the hip+heel+toe
plane, then the forward-ankle-flex / knee-drive-heel-drive move in Phase
1b has propulsive benefit. If the knee were in the plane of
hip+heel+toe, then flexing the ankle would exert force only in the line
of the ski or skate, which cannot have any significant propulsion benefit (unless
the glide wax on the ski base is not working or the bearings on the
skate wheels are bad).
(b) The leg is bent sideways in the middle and
thus slightly shortened by rolling the knee inward. So in a later phase
the knee can be rolled outward and the leg straightened and thus
lengthened. This is propulsive work added by the knee-rotator muscles on
the opposite side, operating to reverse the earlier Phase 1 move by this
side's knee-rotator muscles.
Drive the knee down and forward. Drive the
heel down and back.
This is not a "forward step".
It is rather a "scissoring" of the
legs. The recovering foot goes forward, but the pushing foot goes
backward. The "going back" part is the heel-drive move -- driving
the heel back, so the ankle joint moves behind.
[ ski + klap-skate: ] Driving the heel down and back also helps to
make sure the heel stays down on the ski for the start of
Phase 2 -- to be in position for maximum
transmission of the main leg-extension force.
For me it helps to try out both mental images:
Driving the knee of the pushing leg down and forward; and Driving the
heel of the pushing leg down and back.
- There's usually also some bending of the knee.
This prepares for a larger range-of-motion by
the knee-extensor muscles in full extension push of Phase 3.
Some coaches think that this knee-drive move
is a knee-flex move, and neglect the ankle-flex aspect. I think
the knee-flex interpretation is a confusion of a move with a position.
For the ice and inline speedskating, a position with strong knee-bend is
important for (a) aerodynamics at higher speeds; (b) the knee-extensor
muscles can push effectively through a larger range-of-motion in the
lower-force, lower-gliding-friction context of ice or wheels on flat or
gentle courses; (c) how much and how long a strong knee-bend position
can be sustained is a key bottleneck in ice and inline race performance;
(d) for non-klap ice and inline equipment, it is not so obvious how the
ankle-flex move also prepares for later additional propulsion.
My response to the knee-flex interpretation of
the knee-drive move is: (a) ankle-flex delivers additional propulsive
work immediately in Phase 1b, provided that the inward-knee-roll move
was started in Phase 1a; (b) the ankle-flex move shifts the hip forward
ahead of the ankle, so that the later knee-extension move in Phase 3 has
more of an outward-sideways component and less of a slicing-forward
component, and is thus more effective for propulsion; (c) for klap-skate
equipment, including ski-skating, the ankle-flex now increases the
range-of-motion of the toe-push extension in Phase 3b, which adds
propulsion work.
Note: I find it remarkable that this knee-flexion
move means that there is a definite shortening of the effective leg
extension length during part of the leg-push. Which contradicts the
obvious idea that the leg-push should be a continuous lengthening of
extension. This shortening can work because it comes at an early phase
when the leg is nearly vertical, so the backward and sideways push
components of its leg-pus vector are small, to the loss of propulsion is
small. The main effect of the shortening in this phase is a "lightening"
of the vertical weighing down, which does not significantly affect
propulsive work (unless it makes the foot lose grip to push outward
across the ground). Later in Phase 3 when the corresponding lengthening
occurs, the skate or ski is angled vertically relative to the ground, so the proportion of
the backward and sideways components of the leg-push vector are larger.
So there is a substantial net gain in propulsion work.
- How much angle of forward flex of the ankle? More.
The more angle, the
better positioned are the hip and knee joints for the Phase 3 extension
push -- and the more propulsion work arleady in this phase. It's pretty amazing how sharply the elite ski-skate racers angle
their ankles forward in Phase 1 of their leg-push.
If the knee is angled inward relative to the
aim-angle of the pushing skate or ski -- by using the inward-knee-roll move in
Phase 1a -- then the knee-drive move will be aimed
partly forward in the direction of the skater's overall motion.
So the action of the shin muscle in flexing
the ankle will also be doing some direct forward-propulsion work, by
moving the skater's hips and upper body forward against air resistance
(or against gravity, if going uphill). Perhaps it also helps the leg
muscles push more out toward the side.
? A possible downside is that moving the knee inward
takes it slightly out of the straight line of force transmission. But perhaps enabling the
direct propulsion work by the shin muscle is worth it. The biomechanics
and physics of this get rather complicated. Actually there are several
other cases where the joint-configuration geometry used by winning elite
athletes does not follow the obvious planar alignment that would be
guessed from simplistic biomechanical analysis. Anyway this concern can
be addressed by . . .
Don't forget later in Phase 3 to reverse
roll the knee out into straight alignment in the toe-heel-hip plane.
Key point: Even if allow the knee to angle
inward slightly, do not fall into the tempting corollary of
allowing the hip to swing outward. Because that's a larger deviation
from the straight-line for side-force transmission, a major absorption
-- and without any compensating benefit.
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