[ Print this | help ]

what's here

  • High-speed versus Low-speed angles in poling
     
  • Gearing of Pole-Push versus other motions

see also

back to Top | more Ideas | Secrets | FAQ | Resources | more Classic

High-speed versus Low-speed angles in poling

  • The pole delivers most power at low speeds when it most angled back.
     
  • The pole delivers most power at high speeds when it is close to vertical.

Why:  When the pole is nearly vertical, the same angle of rotational movement from the shoulder or elbow joint (or waist or hip joint) generates 40% more horizontal forward motion than when the pole is angled back at 45 degrees.  The same size muscle-and-joint move matches a forward speed 40% higher.

It's geometry.  The horizontal position of the pole tip is proportional to the cosine of the angle of the pole.  You can see how much change in forward position a 1-degree move in angle makes by getting the difference between cosine of 89 degrees and cosine of 90 degrees.  Then compare that with the change between the cosines of 44 degrees and 45 degrees.

Or from calculus:  The horizontal speed of the pole tip is proportional to the sine of the angle of the pole (because in calculus the sine function is the "derivative" of the cosine function).  The sine of 45 degrees is 0.7071 and the sine of 90 degrees is 1.0000 -- which is 40% larger.

This gearing difference works the other way with forces.  The same muscle tension and joint stresses can generate higher forward-push force (at lower speed) when the pole is more angled back than when it is closer to vertical.   

Therefore:

  • the more vertical angle is the "high-gear" sub-range of the pole-push motion:  better for higher speeds where high force is not critical.  
     
  • the more angled-back pole is the "low-gear" sub-range or pole-push motion:  Better for high forces where high speed is not possible.

Another reason why planting the pole further back is a better match for climbing up a steep hill. 

Note that each pole-push motion always must start in a "higher-gear" part of its range than where it finishes.  

This is a slight disadvantage, because in several motion techniques there is a passive-glide "dead spot" immediately before the start of the pole-push -- so the skier's speed is slowest just when the pole-push configuration is ready for a higher speed.  This disadvantage is greatest when climbing slowly up a steep hill.

This mis-match at the start of a push on a hill-climb is not shared by the big leg muscles, another small reason why the focus moves to the legs for climbing steep hills. 

back to Top | more Ideas | Secrets | FAQ | Resources | more Classic

Gearing of Pole-Push versus other motions

Pole-push compared with Classic Striding leg-push

The pole-push torques (or rotational forces) are applied from the shoulder and elbow joints.  Also from the waist and hip joints, but the forces from these joints must still be transmitted through the shoulder and elbow joints. 

The shoulder and elbow joints are much farther away from the surface of the snow than the knee and ankle joints, and somewhat farther than the hip joint.  Other things being the same, the length of forward motion from a rotating joint tends to be proportional to its distance from contact with the snow surface.   

So the same angle of rotational movement in the pole-driving joints generates greater horizontal forward motion when it comes from the shoulder than from the knee.  The same muscle-and-joint move from the shoulder matches a higher forward speed. 

Therefore the pole-push is a better "high-gear" motion -- a better match for higher speeds than the classic striding leg-push.  

On flat terrain, the pole-tip also has a longer effective distance of contact stopped in the snow than the ski -- but this longer effective range of motion is a separate advantage.

This gearing difference works the other way with forces.  The same muscle tension and joint stresses can generate higher forward-push force (at lower speed) it is applied through joints closer to contact with the snow surface.

This is a very important reason why the knee and ankle joints (also the hip) become the focus for climbing up a steep hill.

Pole-push compared with Ski Skating leg-push

The same arguments for why the Classic striding leg-push is better suited than the pole-push for slower speeds and steep hills apply mostly for the Skating leg-push, since it also uses the knee and ankle joints.

But surprisingly, the Skating leg-push is also better suited than the pole-push for very high speeds.  The problem for the pole-push is that force can only be applied while the tip of the pole is stopped in contact with the surface of the snow.  So pole-tip must be be moved at a speed relative to the rest of the skier's body which is the roughly similar to the skier's forward speed over the snow.  

Skating can apply force while the ski is moving on the snow, so it is not subject to the "stopped on the snow" requirement, therefore the relative speed of the ski does not have to be nearly as high as for poling.  

And controlling the angle of the skating ski out to the side enables a wider range of "gearing" than is available in the pole-push from the vertical and angled-back pole positions.  The skating ski overall has a wider range of speeds over which it can effectively match the skier's desired speed without a fall-off in power delivered.  It performs better than poling both above and below the optimal speed range for high pole-push power.

This analysis fits with how elite racers choose Skate motion techniques: 

  • The pole-push is usually in its "good" Speed-Power output zone at "normal speeds" for gentle terrain -- so the V2 skate motion (Canadian "1-skate") is preferred by elite racers, to use the maximum number of pole-pushes per stroke cycle. 
     
  • At slower speeds up a steep hill, the low-gear inferiority of the pole-push shows itself, so the pole-push is cut back to one per stroke cycle, timed so that it does not interfere with the best timing for the leg-pushes -- V1 skate (Canadian "offset") 
     
  • At very high speeds on flats or gentle downhill, the very-high-gear limitations of the pole-push emerge -- while the skate leg-push can still delive effective power.  So skier keeps on skating, but cuts the number of pole-pushes to none (Skate-No-Poling) or to one (Open Field Skate).
     

back to Top | more Ideas | Secrets | FAQ | Resources | more Classic

[ Print this | help ]