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


Intro

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.

Summary of phases and key findings

R - Recovery phase

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.

0 - Set-down phase

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.

1 - Underneath / Side-of-leg-Out push phase

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.)

  • Phase 1b is the low-power segment of the stroke-cycle. To increase overall average power, find a way to get through phase 1b quicker.

[ 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.

2 - Blend push phase

(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:

  • Theme: Direct push with the two big sets of skating leg muscles, Side-of-leg-Out and Extension.

  • 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.

3Extension push phase

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.

  • Overlap leg-pushes:  Play with setting the next foot down just before starting this final phase of the current foot -- so the early part of Phase 1 of the next leg is simultaneous with the later part of phase 3 of this current leg.

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.]

  • up-down reactive-force:  This can add propulsive power to the skating leg-push, and the end of this phase is a good time for it.

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.

  • forward-backward reactive-force:  This could possibly add propulsive power to the skating leg-push -- and in the special situations where it could, the end of this phase is a good time for it.

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.

 

more . . .

see also

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