[ under construction ]
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.
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
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
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
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
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
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
[ 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.
This phase goes from (roughly) the start of focus on the
knee-extension move. There may be some overlap with Phase 2.
[ physics and biomechanics parameters that drive the
amount of added propulsion work -- and the additional time it takes to
perform that work. ]
?? [ to be added ]
for forward propulsion:
also perhaps continuation of
On icy snow or wet pavement, full extension may not be
possible, because edge grip is gets too difficult when the ski or skate gets too far away from
the down-force from the weight of the skater's upper body.
Extending the knee joint is critical to getting
maximum extension of the leg. The main muscles for this
knee-extension move are the quadriceps.
Extending the knee joint pushes the skate or ski forward
relative to the pushing hip.
The "magic" of skating is that it's possible
to generate a backward push-force by pushing out toward the side on a
skate or ski that is slicing forward.
For me it seems like the foot makes a
circular arc relative to the pushing hip. In Phase 1b the foot goes back
behind the hip. In Phase 2 the foot
goes outward. Then in Phase 3 the foot continues to go out and also comes
forward relative to the hip.
It feels strange because our natural intuition from
walking and running tells us that the foot must move backward in order to push
the body forward.
But the special "magic" of skating is that more
extension of the leg out toward the side gets converted into more forward
propulsion. This "forward slice" or "forward kick" is the true test of the
skater's faith in the power of pushing out toward the side.
[ inline: skate teachers sometimes refer to this
forward slice move as "carving", or as the final phase of the "C-stroke" push. ]
[ Bicyclists may note that it is also possible to use
a "forward kick" move to add power to seated pedaling -- by starting to use the
quadriceps muscles to push the pedal as it comes "over the top" of the circle. ]
There may be some overlap of this move with the moves
in the early part of Phase 3,
but I'm inclined to discourage this, in order to give emphasis to
allowing the longest time for best transmission of big push
forces through the bone structures of the ankle and heel.
[ inline: this phase does not apply to inline skates,
unless they are klap-skates ]
for forward propulsion:
This is the time for the heel to come up off
the klap-skate or ski. The heel should stay down all through Phase 1 thru Phase 3, for
best transmission of the big forces in Phase 2 and Phase 3.
Big Trap: When think consciously about the toe-push,
it's easy to get into pushing only toward the back, and to forget the "forward
kick" of Phase 3 which is needed to effectively gain maximum propulsion from the
knee-extensor / quadriceps muscles. Therefore some instructors avoid mentioning
the concept of toe-push, and recommend that most skaters just allow the proper
motion to emerge naturally from consciously thinking about overall leg
So early part of Phase 1 of the next leg overlaps with
later part of
Phase 3 of the previous leg.
It might be thought that these moves could add to the propulsive
- outward-hip-leg-rotation (or perhaps "outward-knee-roll") - [
- ankle supination - [
see more ]
because they extend the length of the leg -- provided there were
opposite inward-knee-roll and ankle-pronation moves in phase 1 or phase
But the direction of force from these moves is negative for propulsion in the leg-configuration and the start of phase 3.
They do extend propulsive range-of-motion (and slow the fall of the
skier's body mass and the fall of the hip) -- but at the cost of
reducing the propulsive force.
There might be some large angle of the leg leaning away from vertical
where adding these moves is a net positive for propulsive work, but I
doubt at any leg-lean angle normally used for human skating (except
possibly around a very tight curve?). Since it slows the stroke
slightly, even if it is positive for propulsive work, it still might not
be positive propulsive for propulsive power (the rate of work).