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Turnover frequency (or "cadence")

 

Turnover frequency is a key component of the physics of propulsive Power. Many of the the tough problems in maximizing Power are the compromises between improving range-of-motion Distance while decreasing turnover rate. Video analysis tends to give priority to making improvements in range-of-motion distance, because the positions are readily observed by observing the video with the pause-frame function, while Turnover requires some careful counting and calculating.

Turnover frequency is defined as the number of complete stroke-cycles (with pushing by both legs) per minute. So if a skater makes 92 leg-pushes in a time duration of one minute, 46 with the Right leg and 46 with the Left leg, that's a turnover frequency of 46 rpm ("repetitions per minute").

Typically turnover frequency is lower when skating down a hill or cruising for long time on flat or gentle terrain, and higher frequency stroking when climbing up a steep hill, or doing a short intense sprint.

Often it's valuable to explicitly train muscle quickness and neural coordination for higher turnover. One aspect that holds back turnover is slowness of leg-recovery moves. The muscles of leg-recovery otherwise don't get much attention in a training program.

Sample turnover frequency observations:

  • Chad Hedrick doing Double-push for a long distance solo later in a marathon race on gentle terrain: 43 rpm

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Timing synchronization among phases

Finish versus Set-down timing

priority: A

It's easy to overlook this sort of thing because it's not a specific "move".  But it's important because one of the key determiners of the amount of Power (in Watts) from every positive propulsive Work move is turnover frequency. So anything that slows down frequency has a bigger impact than you'd expect -- and so does anything that speeds up frequency.

Changing the timing from "one foot and then the other" to overlapping the pushing by the two feet deserves strong consideration for any skater looking for more power + more forward speed.

The other reason for "overlap timing" between Finish and Set-down is that if the foot newly set down helps support the weight of the upper body, then the other leg can spend more time making its Extension push from a lower hip position. In a lower-hip configuration, a higher proportion of the force from the big hip-extension and knee-extension muscles goes directly into propulsive Work.

This "weight-support" role can be emphasized more (and with more precise control of angular configuration and timing) if the foot is set down at first aiming straight in the direction of the skater's overall motion, then pivoted to aim diagonally.

standard-form perceptual check

The other foot is already set down on the ground before this leg lifts off. The Set-down of the next foot should occur before the Finish of the current foot's pushing: "overlap" timing.

A stronger form of perceptual check is to have the other foot already set down on the ground when the main pushing leg reaches its Midway point (midway between vertically underneath hip and full extention at lift up).

simple Normal-push

Usually the other foot should be already set down on the ground before this leg lifts off. The Set-down of the next foot should occur before the Finish of the current foot's pushing: "overlap" timing.

This (usually) increases propulsive Power by increasing the turnover frequency all the skater's propulsive moves.

exception

The only exception I've seen is in very high-force sprinting situations: e.g. from a standing start in a short time-trial or race, or sprinting up a short very steep hill (on a cross-country snow-skating course) -- often both of the skater's feet are seen up in the air briefly between leg-pushes.

Seems like the skater is pushing so with such a strong fast delivered so quickly that there's no place left for it to go but up. There's always an upward-downward component of the main leg-extension push in skating, and it vertically raises the mass of the skater's upper body during the early phases of the leg-push -- but normally the vertical rise of the upper body is not so high that it pulls the feet up off the ground with it.

The obvious interpretation of how this exception works is that the increased Force of the leg-pushes adds more propulsive Work + Power than the time gap between pushes subtracts. There are always trade-offs among the main components that determine the amount of Power.

The other interpretation is that sprinting skaters would have even more Power (in Watts) if both feet did not "go airborne" and they eliminated the gaps between strokes -- but time delays in their neural-muscular control networks do not permit this level of precision in ending such a strong push.

I remember seeing a study with force sensors on bicycle pedals which indicated that sprinting cyclists would often "overshoot" on the timing of their main leg-extension push, which hindered the phase of their stroke -- but the additional positive work from the extension push was more than the loss in the next phase, so the "overshoot" in timing was worth it. 

Double-push

The other foot is already set down on the ground before this leg making its outward main push lifts up off the ground. The Set-down of the next foot should occur before the Finish of the current foot's pushing: "overlap" timing.

This "overlap" timing applies even to the "hopped" Double-push (a.k.a. "W skate") done on skis for snow-skating. The hop is performed as the Aim-switch move between the inward and outward pushes by the same leg. But when the other leg is Set-down for its inward push, it overlaps on the ground with the Finish of the previous leg.

Sometimes the Set-down of the other foot is as early as Midway through the main outward push. Initially the other foot does not push much. It mostly helps support the weight of the upper body so the main pushing leg's hip can stay lower longer during the Extension phase. There may (should?) also be an overlap of pushing by the two legs, but that overlap has a smaller time duration than the overlap of both legs down gliding on the ground.

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Wiggly versus Stable core

When observing videos, it's valuable to develop a "feel" for the overall rhythm and larger patterns of sound technique -- beyond observations of certain body parts in a specific phase of the stroke. One problem that some experienced coaches watch out for is skating "wiggly" -- seen in the front or foot-aim view (not from the side).

What is desired is the opposite:  a consistent "unison" pattern of movement of the body parts as seen in a front view. The foot is pushing toward one side, and all the other body parts are moving toward the other side, away from the push. The higher off the ground you look, the farther each body part is moving -- so in a front view the body parts form a (roughly) diagonal line which is tilting away from the push.

Each part should be moving sideways at least as far as the body part below it. The physics of this is that it's a careful exploitation of Newton's Third Law: managing both ends of the push-force, reaction as well as action.

Most skaters have no perception of whether they're doing this or not, so just telling them to move their parts in "unison" usually won't help much. So they need an observer to point out the "wiggle" problems and suggest corrections.

The problem for the observer is that "wiggly" parts are often the ones "buried on the middle" -- the parts most difficult to observe. The easiest parts for an outside observer to monitor are usually the "extreme" outer ones: hands, head, feet. Next in easiness are the shoulders and knees. What's more difficult to observe accurately is just above and below the hips.

That's why getting good at sensing the "feeling" of wiggle versus stability at the core is so helpful -- to quickly detect the presence of some problem, before doing the labor of careful analysis or measurements.

Wiggles in hips and below are better seen in a foot-aim view. Wiggles in hips and above are better seen in front view.

Some typical "wiggles":

  • knee moves away from the push, but hip moves toward the push -- (more accurately see in foot-aim view, sometimes in front view this looks like a wiggle but really isn't, especially when climbing a steep hill).

  • hips move away from the push, but torso + shoulders move toward the push. (Watch for this in sprinting from a standing start).

Other possible wiggles:

  • ankle moves away from push, knee or hip moves toward the push.

  • torso + shoulders move way from pufh, arms + hands move toward the push. (Watch for this in Double-push with arm-swing).

Counter-acting wiggle and building a "stable core":

  • first just being aware of the problem.

  • develping new strength and endurance in specific muscles

Hip-abduction muscles for hip-knee instability in the main outward push. Certain muscles in abdomen and lower back to counteract "wiggle" in hip-torso-shoulder.

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more . . .

 

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back to Top | more Video | more topics | Resources | Go by Skating index

more . . .

?? [ to be added ]