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Inline Evolution: The Changing Face of Technical Character

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The Double-Push: Part 1

© Barry Publow, BPE, CFA

Yup! Good things do come to those who wait. That's right.....I finally got my own column. Now I can babble to the masses on a regular basis about my favorite subjects. This column is dedicated primarily to issues of training application, technique, and other biomechanical and physiological perspectives. My debut topic for this column is one that will interest many. It concerns the changing face of technical character now occurring among the inline world, and my subjective theory as to why this technique is superior. Bear in mind that much of what follows is, at this point, purely speculative and my own opinion. However, everything I say is founded within logical, sound and proven mechanical principles and known processes of performance physiology.

Circa 1993

It was the strangest thing I had ever seen.....Chad Hedrick at the 1993 Junior North American Championships in Cambridge, Ontario, Canada. It was there that I unknowingly witnessed a precursor to the beginning of a new technical era. We Canadians who, were taught to skate very "ice-like", watched in awe-inspired wonder as Chad demonstrated what to us was a radically different technical method of skating. His technique was not only bizarre, but it went against everything that we had ever been taught about the basic technical components of speedskating. This technique was immediately given descriptive names like "the scissor" and "the criss-cross". Otherwise, it was simply known as "the Chad". From that day to the present moment that I stare at my computer monitor, I remain fascinated by this technique. As a coach and fellow skater, I am intrigued by the technical aspects of what makes this thing work. As a kinesiologist by profession, I am further intrigued by the magical and mysterious link between biomechanical observations and physical processes that make this technique so darn good.

Circa 1994-1995

The 1994 World Championships in France. I watched Chad drop jaws, not only because of his seemingly effortless and graceful power, but because he was skating different than virtually everyone else. Seven months later at the '95 Pan American Games in Argentina, many skaters had adopted (or should I say copied) this technique. The Colombian's, in particular, had gone to great lengths to be taught to skate like Chad, including recruiting the Australian coach Bill Begg to teach their skaters to emulate Chad.

Present

Chad continues to dominate the domestic and International racing scene. Many of the top skaters in the US and abroad now skate somewhat like Chad. I am not necessarily suggesting that all these pros copied Chad. Through similar exposure, they too may have experienced a parallel technical evolution towards this method of skating. However, it is my best guess that most of these skaters incorporated some of the mechanical characteristics that Chad displayed.

Style Vs Technique

Today, this technique is most commonly termed the double-push. Many skaters and coaches mistakenly use the terms "style" and "technique" interchangeably. Technique refers to the raw mechanical components, that when executed, produce the actual movement pattern. Style, on the other hand, refers to the individual flare, or signature, that an individual adds to these basics. Because of this, two skaters with the same technique can appear very different in form. When dealing with proficient skaters, it is usually style, not technique, that allows us to distinguish one skater from another. Another concept I like to use when discussing technique is "extremes". This term particularly applies to the double-push technique. Classic speedskating technique is very precise in it's application. That is, the range of movement variability that is possible within the scope of proper form is very small. By contrast, the double-push allows a much broader range of possibility. This is to say that it's movement pattern allows a high degree a variability when being performed. This fact constitutes one of the indirect performance advantages of the double-push.....it allows a skater to wander between the possible extremes of application. Different situations (e.g. sprints, accelerations, steady tempo) seem to have an optimal set-point within these extremes. Skating with the double-push therefore gives a skater a more diverse range of "gears", and therefore a more effective arsenal of tools to be used in race conditions.

What is it?

Transforming a dynamic, complex movement pattern like speedskating into words on a page is a vexing task. At times, a photo can be worth a thousand words. But in this case, a picture can only depict a brief static instance at a single point during a fluid motion. The photos included in this discussion have been strategically taken to best illustrate and supplement verbal description of a specific point in the movement. However, this technique remains very difficult to conceptualize into a mental image, particularly if you have never actually seen this technique before. We all know that the sport of speedskating is about power output, and how efficiently this power can be applied through technique. Technique itself (or, part of it) is about working within limits. As ice skaters, we execute whatever biomechanical events we can within the allowable limits and potential of the blade on ice. The fact is, with inline skates these limits are much broader. Because of this, classic ice speedskating technique, which involves pushing and gliding from a relatively static position, is not necessarily the most effective technique on wheels. Am I about to commit sacrilege against the church of ice speedskating? Do I dare declare that there is a superior way to inline that to use ice technique? I guess so because it's true folks! So if there is a better way to skate, why haven't the ice skaters figured it out yet? The answer is quite simple.....it won't work on ice. By the end of this series, you should be able to see why.

The Double-Push

This technique is so named because it involves two pushes instead of one. Say What?! As opposed to classic technique, the double-push allows a skater to apply external power in two separate ways. Let's begin with a thorough breakdown of the individual components.

1) The Glide Phase ("The Pull")

Classic speedskating technique involves a static glide. That is, the support leg is positioned directly under the body and glides in a slight outward arc. I like to call this glide the "banana" because of the shape of the tracing left by the skate. During this period, the muscles of the hip and leg are engaged in a static (isometric) contraction. All of the energy used to support the body weight during the glide is used simply for support. In other words, none of this energy is used for generating propulsion through it's application to external power output. By contrast, the double-push technique allows the skater to use some of this energy to help produce force and reduce the process of deceleration that occurs as the glide progresses. How is this accomplished? With the double-push, the glide (support) leg first arcs inward and actually crosses under the midline of the body. What this allows is an active "pulling" of the glide leg towards the midline almost simultaneous to the pushing of the opposite leg. Thus, it isn't really a push, but a pull. To accomplish this inward arc at the beginning of the glide, the skater must "edge" the wheels of the glide leg significantly on the outside. The positive pressure on the outside aspect of the wheels will help ensure that the skate glides inwards towards the body.

2a - Beginning of Glide Phase, Onset of "Pull" 2b - Late Glide Phase, Terminal Point of "Pull" 2c - Weight Transfer, End of Recovery Phase 2d - Beginning of Push Phase, Setting up for "the Pull"

Film strip1 depicts body position during classic "ice" technique. In Figure 1c, notice how the glide leg is held in a static position directly under the hip of the same leg. Film strip 2 shows one full cycle of the double-push. This same point (ie. glide phase) in the movement is shown in Figures 2a and 2b. As you can see, there is a distinct difference in body position between image 1c and those of 2a and b. In the double-push, the support leg comes under the body across the mid-line. That is, the glide skate moves towards the middle of the body so that it goes under the imaginary vertical line drawn down from the hip. This is the main discernible difference between these two techniques. Remember, during this inwards motion of the support leg, the skater actively "pulls" the leg towards and under the mid-line.

2) The Push

With this technique, the push progresses in much the same manner as it does with conventional technique. However, because of the position of the support leg at the onset of force application, the push begins from a different position (Figure 2b). This fact constitutes one of the main advantages of the double-push technique. Why? Because starting the push from across the mid-line effectively lengthens one's push displacement compared to conventional technique.

3) The Recovery

The purpose of the recovery process is to set up the skate for the next stride. On inlines, a skater decelerates much faster than one on ice. Therefore, minimizing glide time, and having a faster stride frequency, is advantageous to the inliner. Using the traditional "circle around the back" recovery from ice skating basically wastes valuable time. This movement also stimulates the tendency for a more static glide and does not set up the recovery skate for a good set-down position. As a result of these facts, the recovery in the double-push is basically straight inward from the position it leaves the pavement. Some skaters draw the recovery leg directly inwards to a position where both knees are basically together, while others direct the recovery leg in so that it sits almost directly behind the support leg. Others still pull the recovery leg so far inwards that it moves behind and across the support leg. Regardless of which specific "extreme" of the recovery is implemented, the point is that momentum from drawing the recovery leg forcefully inward helps facilitate the powerful "pulling in" action of the support leg

4) Set Down

Classic technique involves setting the recovery skate down almost immediately beside and slightly ahead of the support leg skate (Figure 1a). This final stage of the recovery process coincides with the weight transfer and lateral shift in the centre of gravity (Figure 1b). With the double-push technique, the set-down occurs significantly more to the outside (Figure 2d). This is a crucial step in the entire sequence. Setting the skate down too close to the mid-line will shorten the pulling action to the point where it is rendered useless. If the skate is set down too far outside, it will also reduce the effectiveness of the pull and likely result in poor balance. Therefore, much practice is usually required to master this important step in the stride. It is also important to remember that the recovery skate is set down on the outside of the wheels. As soon as weight is applied to the recovery skate, it then becomes the support leg which begins the inward pulling motion. As this occurs, the skate progressively angles to the outside, creating even more positive pressure on the lateral part of the wheels, thus facilitating the inward movement. If you look at the wheels in Figure 2a, you can see how they are angled considerably on the outside in just such a manner. The third important aspect of the set-down concerns the direction, or angle, of the skate frame once it touches down. Notice in Figures 2a and 2d how the recovery skate is set down so that the skate and wheels and angled inwards. This not only helps to facilitate the inward pulling motion, but concentrates the effort more specifically on the adductor muscles of the inner thigh. All of these factors in the set-down are critical for allowing the double-push to work effectively. Therefore, much practice is usually required to master this important step in the stride. . The purpose of part 1 of this article is to use a combination of illustration and verbal description to help readers understand what the double-push is, as well as details of it's breakdown. Part 2 in the next issue will describe the physiological and biomechanical reasons why this techhnique is, or can be, superior. Also, the next segment will include information on drill progressions that can be used to help learn, develop, and/or hone your own personal technique.

The Double-Push (Part 2 of 2)

If the wave hasn't hit you yet, get ready! If you're not using it now, you better start learning how. The word is out. The Double-push technique is taking over!

The first part of this article described the differences in technical and mechanical events between classic speedskating technique and the still evolving realm of the double-push. If you've been to one of the many larger races, you've probably seen it before. If you've ever seen Chad Hedrick skate, then you know what I am talking about. Chad may have introduced this technique to the World, but he is now only one of a great many skaters using some version of this technique. Even that being true, Chad is a true wonder on wheels. To the untrained eye, he may not be the prettiest to watch. But to those in the know, he is undoubtedly the best double-push skater around. Is this the secret behind his rise to the top and his continuing dominance? I would say no, atleast not entirely. But, it is safe to say that his proficiency and mastery of this technique commonly know as "the Chad" undoubtedly has helped him mow down the competition along the way. For those of you who did not read part 1 of this article in the last issue of Speedskating Times, here's a quick review.

The Double-Push Defined

The double-push involves two pushes instead of one. This technique allows the skater to apply external power output in two separate phases during the stride. This is accomplished by transforming the usual static glide phase into one that is dynamic in nature. This diminishes the process of deceleration, thus maintaining momentum through the additional application of propulsive forces. Practically, this involves an active inward pulling of the support leg during the glide phase. As such, the glide leg does not remain stationary under the body the way it does in classic technique, but rather continues across and under the mid-line of the body. This "pulling" action of the glide leg is performed by edging the wheels on the outside with the foot turned slightly inwards at the beginning of the set-down. This positive pressure on the lateral aspect of the wheels not only directs the leg in an initial inward arc, but provides a measure of leverage for the adductor muscles to pull the leg towards the centreline.

Although the push occurs in much the same fashion as classical speedskating technique, the recovery process is considerably different. Rather than circling the recovery leg around the back and setting it down almost immediately beside the support leg, the recovery process of the double-push is markedly different in it's application. That is, the recovery leg is drawn almost directly inwards at the end of the push, and is set down significantly to the outside of the body. This critical event is important to execute properly as it is comprises an essential link in the overall chain of movements.

Unlocking the Mystery

So now we know what the double-push is. But what is the secret behind it? What is it about the biomechanics of this technique that makes it so good? And what is the magical link between mechanics and physiologic events that makes it efficient? What follows is my subjective theory to answer these questions. My analysis of this technique is purely speculative at this point, but is founded within logical and proven principles of mechanics and performance physiology.

1) Two Pushes are Better than one

The main direct reason behind the superiority of the double-push is the fact that positive work can be performed during what is normally a static, energy-inefficient glide phase. The pulling of the adductor group (upper, inner thigh), using leverage created by the outward angle of the wheels, helps to generate propulsion in much the same way that the lateral push to the side uses the inner edge of the wheels to produce forward motion. The double-push therefore allows a skater do more total work per stride than any other method of skating. But doesn't this mean twice the energy compared to "single-push" classic skating? The answer is no! During classic technique, considerable contractile energy is utilized simply to support the body weight over the glide leg. This is quite inefficient and is really wasted energy. The double-push takes this energy and finds a constructive way to use it for maintaining speed during the glide, and creating additional propulsion.

2) Increased Push Displacement (Stroke Length)

For those of you who have read John Banks' articles in the past, you have learned that one of the best ways to go fast is to increase push displacement- the distance the skate travels sideways from the onset of force application to the terminal point of the lateral push. John is quick to point out that the only way to achieve a longer push displacement is to sit lower. Doing so means a smaller pre-extension knee angle and therefore longer stroke length. As we all know, a deep seated knee angle comes at a cost. Research shows that squatting low in deep knee flexion during skating increases the relative level of isometric contraction of the quadriceps muscles, thereby increasing intramuscular pressure. This pressure serves as a major limiting factor in speedskating performance because it temporarily restricts muscle blood flow. The result is a more rapid accumulation of certain metabolic substances (eg. lactic acid) that interfere with the excitation-contraction coupling of the muscle fibres. This represents a classic catch 22 situation: Sitting low is required to achieve a "long" push. But, doing so is very taxing and can result in the early onset of local muscle fatigue. The double-push doesn't entirely solve this problem, but serves to reduce the strength of the relation.

Here's how:

Allowing the support leg to come under the body and across the mid-line during the pulling part of the glide means that the push is initiated from a more inward position. Therefore, given the same pre-extension knee angle, the total push displacement will be increased. From the above testimony, it can be seen that increasing push length without any lowering of the knees is a desirable thing. Another way to look at it is this: the double-push allows a skater to sit higher (ie. straighten the knees) while maintaining the same push length achieved by a lower sitting "classic" skater. Either way you look at it, the result is the same.....increased mechanical efficiency without additional claim to physiologic responses. Therefore, there is another way to increase push displacement without squatting lower - switch to the double-push technique. The "higher" position it allows may have a small but measurable increase in frontal surface area, and therefore drag (air resistance). However, the advantage is a rather enormous subjective feeling of power resulting in the detection of a noticable decrease in lactate accumulation in the working muscles.

3) Reflex Potentiation: Stretch-Shortening Enhancement

A well-documented physiological observation is the fact that a muscle that is quickly elongated due to stretch or rapid eccentric (lengthening) movement results in a stronger and more powerful concentric (shortening) contraction. This "rebound effect" likely occurs with the double push technique. Allowing the glide leg to quickly pass under the mid-line stretches the abductor muscles of the hip. Doing so stimulates muscle stretch receptors, giving the following push-off contraction a slight, but significant "potentiation". The end result can be expressed in one of two ways, both reflecting an increase in mechanical efficiency:

Increased strength and power output can be increased with similar effort/energy expenditure

Less effort/energy is required to produce the same level of force output that would be generated using a similar non-potentiated push with classic speedskating technique. In addition, the terminal position of the support leg at the end of the pull (ie. across and under the mid-line) places considerable tension in these abductor muscles. As we know, muscles have elastic properties. This is to say that when a muscle is stretched past it's resting length, passive resistance is developed within the contractile component of the muscle fibres. When the push-off begins, the skater can rely on this helpful stored energy that is released during elastic "recoil", much like a rubber band that is stretched, will return to resting position once released. As the leg now begins to move back towards the normal position of push-off, the tensile stress and force level in the adductor pushing muscles is now higher than would be observed from a strictly static position. This higher initial force level also contributes greatly to absolute force production.

4) Momentum

With the double-push technique, the legs are engaged in almost continuous lateral motion. During the recovery process, the free leg may actually move behind and across the support leg in order to help offset the imbalance created with the glide leg being across the far side of the mid-line. From this position, the recovery leg can be actively "thrown back" towards it's original side as the support leg now begins to generate force and push to the side. Both of these facts are intended to imply that momentum can be used in a positive way to complement force production, maintain velocity, and enhance efficiency through energy savings. Whereas classic technique involves pushing from an almost completely static position, the double-push allows a skater to use this momentum from the recovery leg to enhance push-off force as the support leg begins to extend.

5) Gear Selection

The first part of this article discussed the concept of extremes. With respect to the double-push technique, this refers to the diverse range of movement variability that this method of skating has to offer. Different situations (eg. accelerations, steady tempo, downhill) seem to have an optimal set-point for effectiveness within these extremes of application. With classic speedskating technique, there are very few variables to manipulate in order to adapt to different situations. In fact, the only functional variable a skater has with classic technique is stride frequency. The double-push offers a skater greater means of altering technique to match each specific situation. In effect, the skater using the double-push has more "gears" available. Not only can the double-push skater alter stride frequency (tempo) and push displacement, but he/she can manipulate other critical factors such as the angle of the wheels (affecting leverage of the pull), distance which the glide leg pulls and arcs inwards under the body, amount of overlap of the recovery leg behind the support leg to utilize momentum and supplement push-off forces, and the amount of upper body movement (which can contribute to and enhance leg forces if executed properly).

Because classic technique is very precise in it's execution, it allows very little room for an individual to alter, or customize, the technique to his or her liking. With the double-push, these various factors allow a skater to experiment more until the right combination of elements is found to create a comfortable style for that individual. Paul Hedrick (Chad's coach and father) tells me that Derek Parra can virtually replicate Chad's exact technique. However, Derek apparently does not find this as effective as his more customized version of a more subtle double-push. This is a perfect example of how the double-push allows an individual to manipulate certain performance factors to suit their liking.

My prediction is that within another year, very few successful skaters will be racing with classic technique. Since we often admire those in our sport who are on the podium, there will likely be a continuing trend towards the double-push technique. More and more novice and intermediate skaters will be adopting the characteristics of these successful skaters until virtually no one will be using classic technique on wheels, eventually making it obsolete...a relic of our history. Evidence of our species progressing towards a superior and more effective method of performing a task. After all, Sir Darwin.....isn't that what evolution is all about?

The Double-Push Technique (Part 3)

The reader response to the two-part articles on the double-push has been rather phenomenal. I have received e-mail messages New Zealand and Japan, and phone calls from as far way as Hawaii. It seems that many skaters are encountering problems understanding how the double-push works. Others simply have questions about some of the content from the previous articles. One fellow reader was keen enough fax me a 2 page letter outlining her questions. It is my guess that there are many others that would like to hear the answers to these and other questions. So here we go folks....hold on! What follows are paraphrased quotes from reader responses.

> “your first assertion is that the glide leg does nothing but support the body, and therefore, is a waste of an isometric contraction”

This is not exactly what I stated. The isometric contraction that occurs during the glide phase of classic technique is not “ a waste” as it does serve a fairly useful purpose: supporting the body mass during the glide. My point is that none of this energy is directly used to generate propulsion through external power output to the road. Research has shown that oxygen consumption for holding a static contraction without any benefit to external power lowers the overall efficiency of the exercise mode (Astrand et al. 1986). My point in discussing this business about static contractions is that, for many reasons, dynamic (either concentric or eccentric) contractions are usually preferable. Static contractions not only interfere with muscle blood flow, but result in the activation of antagonistic (opposite) muscles, increasing the force level of the muscles which have to perform positive work (Van Ingen Schenau et al. 1983). These types of repeated contractions also tend to force muscles towards anaerobic metabolism, resulting in the early onset of peripheral muscle fatigue. Research also shows that this local muscle fatigue determines to what extent a skater can utilize their full aerobic capacity (Van Ingen Schenau, 1983). The double-push helps find a way around the negative impact of these detrimental isometric contractions by transforming the usual static glide into one that is more dynamic in nature. The way the leg muscles function during the glide of the double-push is not entirely dynamic, but not altogether static either. However, the significant change in muscle mechanics does appear to have a noticeable effect on intramuscular tension, and therefore the clearance of lactate from the working muscles. This, I believe, is probably the greatest benefit of the double-push.

> “What about the fact that in classic style, when the recovery leg has completed its circle and is about to be set down slightly ahead of and next to the support leg, there is significant forward thrust generated by the recovery leg, which then becomes the support leg? If the classic technique is eliminated in favor of directly pulling the recovery leg inward, the forward thrust generated by the recovery leg coming forward and through at the completion of the circle is eliminated.”

I am not entirely sure what this comment is intended to imply. I don’t think that the word thrust is entirely appropriate for what this individual is trying to say. Thrust implies...a sideward force of one part of a structure against another part (Websters). The recovery process of classic technique certainly does involve placing the skate of the recovery leg significantly forward of the glide skate in preparation for the upcoming push. However, this action does not result in any direct measure of propulsion. Rather, jutting the recovery skate forward facilitates weight transfer and reduces the likelihood of needless rotation of the trunk. Also, this helps to “prime” the upcoming push by placing the skate in a position that will be able to generate more force and forward momentum. Remember, the recovery process of classic technique is simply a method for regrouping the legs, executing lateral movement of the centre of gravity, and preparing for the next push. Although I do state in my article that “the recovery in the double-push is basically straight inward from the position it leaves the pavement”, the analogous “priming” that takes place with the jutting forward of the recovery skate in classic technique still occurs. Here’s how: the glide phase of the double-push involves an inwards motion of the leg, thereby generating additional propulsion. The leg continues to travel inwards to a position where it may actually cross under the vertical midline of the body (photo 2b). However, the terminal position of this pulling is forward enough so that the relative position of the two skates, following completion of the recovery, is virtually identical to the “jutting forward placement” described in classic technique. Therefore, although the recovery pattern is significantly different, the double-push does allow for the same “thrust” and priming for the push as does classic technique.

> Additionally, I have read that a skating technique where a skater pulls the recovery leg directly inward as opposed to using a circular motion is less efficient for physiological reasons that I can’t remember now.

I am not aware of the source of this information, but I can tell you that the researchers who drew this conclusion would have been using classic technique in their methods. There is no doubt in my mind that the semi-circle recovery is the best way to execute regrouping of the pushing leg with classic technique. This is because the weight transfer is so vital, and placement of the blade on the ice must be exact. With the double-push, the outward placement of the recovery skate at the moment of set down dramatically changes the appearance (but not the importance) of the weight transfer. Therefore, the relevance of the semi-circle recovery towards facilitating a smooth “fall” and transition to the push phase is diminished greatly. In addition, inliners use a much higher cadence (stride frequency) than ice skaters. Ice speedskaters have such a low level of friction that they can, and should, maximize their glide time on the outside and flat part of the blade. Using a semi-circle with the recovery skate allows time for this to occur. Inliners, facing much higher levels of surface friction, need to stroke more frequently in order to avoid the more rapid deceleration. Saving time in the recovery phase by drawing the skate almost directly inwards is the best to speed things up in this respect.

> You’ve boldly stated that ice skaters don’t use “the Chad” on ice because they can’t. Why can’t they?...I don’t see any reason why ice skaters couldn’t utilize the same technique”

I will have to speculate why this technique won’t work on the ice, but trust me......it doesn’t work. Many of my skating friends who use the double-push on inlines have all found out the hard way when attempting this on ice (fortunately, ice doesn’t tear out chunks of flesh when you fall). As we all know, blade placement on the ice must be extremely precise. By contract, wheels are very forgiving, and allow for a much broader scope of application. Blades are hard, very thin strips of steel that allow only a few inches of surface contact (depending on the rocker). Wheels, on the other hand, deform relatively easy, are wider and more stable, and are simply more versatile. The answer to the question of why the double-push does not work on ice lies somewhere within these facts. However, my theory why has to do with surface profiles and the fact that an inline skate offers 5 individual areas of surface contact. Speedskating blades, because of the very way they are sharpened, are square on the bottom with a sharp edge on both sides. The outside edge is used for maintaining control during the early glide, the flat part for achieving the lowest running resistance late in the glide, and the inner edge for pushing off. Inline wheels have a much different profile. Speed wheels have an elliptical shape. What this means is that as the wheel rolls from side to side, the direction and magnitude of vertical pressure on the wheel also changes. Also, a racing skate has five separate and small patches of surface contact with the road. The bottom line is likely somewhere between physics and mechanical principles, but my bet is that it is the surface profile of wheels versus a blade that explains why the double-push won’t work on ice. Besides, considering all of the other differences and variables between the two technique, the double-push may not be superior on ice the way I believe it is on the road.

Re: “Your second assertion is that by starting the push from across the mid-line lengthens push displacement.

> “As I understand it, while the push leg is beginning it’s push, the recovery leg is setting down for the pull (photo 2d).”

Not exactly. The push leg begins it force initialization and initial movement during the end of the recovery as the recovery skate is being “thrown” out to the side (photo 2c). The recovery skate is not set down to begin it’s pull until the pushing leg has completed about 90% of it’s push (photo 2d). In this way, there is slight overlap and for a very brief instant, the push and pull are occurring at the same time. In this way, there is constant force being applied to the road.

> As you’ve stated, the set down for the recovery or pulling leg must occur in a position significantly to the outside of the position utilized in classic technique. If this is the case, simple physics would dictate that the end of the push on the pushing leg would have to be > truncated in order for the pulling leg to be set down so far to the outside”.

Yes, the recovery leg must be set down more to the outside of the body than in classic technique. If the adductor muscles are to be able to generate propulsion by pulling inwards towards the midline, they must be stretched first. I am not sure which principle of physics you are referring to by stating that the terminal point of push displacement would have to be shortened because of the placement of the recovery skate. I am by no means a physicist, but I fail to see the connection you are trying to make. If we assume that a 90 degree knee bend starting from a vertical position results in a lateral displacement of 60 cm, then a 90 degree knee bend beginning 10 cm across the vertical would result in a displacement of 70 cm. Granted, this would not be possible if the hips were to have moved laterally in the opposite direction of the push (making it impossible to reach the same point of extension). However, the lateral movement of the hips has not occurred yet, and does not do so until after the push has finished and the pulling action of the opposite leg begins. Also one should keep in mind that once the support leg passes under the midline and continues to travel inwards slightly, the knee does extend slightly. For example, the knee bend may be 90 degrees directly under the hip, but as it passes under and across the midline, this angle may be more like 95 or 100 degrees. This is how push displacement is increased without observing any decrease in pre-extension knee angle.

> “How is it that the skater gets from such an extreme outside edge of the pulling leg where the pulling leg is significantly across the midline (photo 2b), to photo 2d which depicts the beginning of the push phase on an inside edge with the recovery leg placed well outside of the body setting up for the pull?...This seems to be the critical step in the whole process, and I can’t figure out how it’s done”

I agree that there is a fairly large visual step missing between photos 2b and 2c. It was very difficult to sequence the shots in a manner that depicted each and every important step. Let me try to explain verbally how a skater makes the transition from the outside edge at the end of the pull, to the end of the recovery where the push begins on the inside edge of the wheels. Recall from part one that the pull of the glide phase involves an inward arc of the support leg skate. During this time, the skater is using the outside edge of the wheels for leverage and to direct the skate inwards towards and under the midline (photo 2b). The recovery leg, which has now just lifted off the road, acts as a sort of counterbalance - allowing the skater to maintain equilibrium while the glide leg is actually under the midline). At the terminal point of the inward pull, the recovery skate begins to draw inwards and reaches a position almost directly behind the support leg. During this process, the skater must allow the skate to reverse its track on the road as it now begins to arc back in an outwards direction. This should occur quite naturally, guided by the diminishing degree of counterbalance provided by the regrouping recovery skate. Thus, the skate of the glide leg has traced a sort of “s” in the road. The moment the skate begins to arc in this outward direction and rolls over the top of the wheel, the skater uses the momentum generated from the arc, in addition to muscular force, to propel the leg outwards into push-off (photo 2c). Note that early in the push the recovery skate has not yet been set down.

> “Isn’t there a huge loss of forward momentum due to the extreme lateral movement of the skater?”

On the contrary, it is the extreme lateral movement of the legs that results in the forward propulsion of the body. There is actually very little sideways displacement of the body itself. Propulsion is generated during the push and the pull in much the same way that freestyle skaters negotiate pylons on a street course. Aggressive skaters go through a series of straight line pylons spaced a few metres apart. To do this, they use some of the same principles as the double-push ie. the support leg travels across both sides of the midline in an “s” shape, using both sides of the wheels for leverage and propulsion.

> Finally, has anyone done any studies about the efficiency of this technique?”

Not to my knowledge. I would certainly like to be the first one to study this technique in-depth from both biomechanical and physiological perspectives. Anyone out there interested in funding such research? The double-push is so new that I think I am the first one to even describe it in detail.

> Maybe Chad is simply one of those freaks of nature like Miguel Indurain or Greg Lemond who has enormous VO2max combined with great strength which enables him to simply overpower the competition, regardless of the technique he uses.”

I don’t know if Chad has ever been tested but I’m sure that his VO2 would top the charts. Regardless of this, the double-push has made a huge impact in the current pro racing scene, and has resulted in big improvements for many skaters. Here in Canada, I have personally witnessed many improve their times/performances through such technical manipulation alone. Chad is not the only high-profile skater to use the double-push....how about Derek Parra, K.C. Boutiette, Jonathan Webster, Derek Downing, Jorge Botero, Jondon Trevena, and virtually every pro skater out there. I have yet to see a skater on the podium at a major event that doesn’t use some version, albeit subtle, of the double push.

The Double-Push Revisited (Part 1 of 2)
Copyright 1997 Barry Publow

Part 1 discusses the set-down mechanics of double-push skating. The next article in this series will cover the pulling action of the support leg.

Several months have passed now since the last article in the double-push (dp) series, and judging by the response, you skaters seem hungry for more. I received e-mails and phone inquiries from all over asking for tips, drills, pictures, and further explanation. So the time has finally come to revisit what seems to be one of the hottest topics in the world of speed today. Much like this technique continues to evolve as more and more skaters learn double-push, so too does my thinking about the mechanics of the double-push and what makes it work.

Without doubt, there are a whole lot more skaters using the double-push than there were only a year ago. However, the number of skaters who do it well and are able to extract the full potential this technique has to offer is still very, very small. What I mean by this is that many skaters can execute some of the characteristics of dp skating while at a moderate, steady speed. But what they have not yet developed is the “full-blown” version: the ability to utilize the wide range of movement possibility and to accelerate in an effortless and efficient manner unfathomable to a classic skater. One of the profound advantages of the double-push is the economy of motion that is available during such situations of mild to heavy acceleration, whether for surges initiated solo or for those in response to a breakaway or abrupt increase in pack speed. One of the more interesting aspects of the dp for me is this transition in movement dynamics from a steady speed to full-blown acceleration, and the actual changes in stroke mechanics that take place. This process is complex and will require a discussion in itself, but suffice to say that during acceleration several things should happen:

The knee of the of the support/pushing leg bends deeper.
The “pulling” support leg crosses further under the body’s midline.
Once the support/pulling leg reaches the furthest point across the midline and under the body, there is a more noticeable extension (straightening) of the knee.
The skate set-down occurs further to the outside.
Stride tempo increases

When skating at a steady speed, a skater must generate enough force to overcome air and surface resistance in order to sustain a given velocity. Since we know that a deep sustained knee bend and long static glide result in the build up of lactic acid in the leg muscles, a simple solution is to elevate the knees to a shallower angle. However, this immediately compromises the length of push displacement and adversely affects force output. The double-push allows for such a lesser knee angle while maintaining push length by increasing the degree of lateral movement at the hip joint. In other words, the dp technique relies on having the skate of the glide leg begin to push from under and across the middle (midline) of the body (Frame 1). The support leg skate is permitted to reach this point by allowing adduction of the hip i.e. movement at the hip that allows the leg to move towards the center of the body. This end-pull, pre-push body position is key to the numerous advantages dp skating offers.

OK so this is great, right? The pushing skate has to begin from under and across the midline. But how does it get there? BINGO! The answer to this is where the real magic is found, and so too is the most difficult aspect of dp skating......the set down.

The Set Down is Crucial!

After nearly 3 years of trying to learn the double-push, perfect it, and teach it to others, likely the most difficult related skill to acquire is the set down of the recovery skate. This aspect of dp skating, and the chain of movements that follow, is so integral to the overall motion that without it the double-push cannot exist. Not only is this the most difficult portion to learn, but it remains the most difficult to explain verbally (which is why I have finally made an instructional video tape to teach double-push skating...details in “Skate Gear” at the back of the issue). Grasping the basic premise of the set-down mechanics in a conceptual or visual framework is one thing, but putting them into practice is an entirely different and more difficult matter.

The following video photo sequence depicts changes in body position from the terminal point of the inward pulling leg, to the precise instant the recovery skate touches the road.

Frame 1:

The support/pulling leg has reached the furthest point under the midline of the body. Notice that the wheels roll on the outside edge. The free recovery skate is in the final stages of regrouping behind the support leg.

Frame 2:

The support leg skate has rolled over onto the inside edge of the wheels and begins to track outwards as it initiates a push. In classic technique, the skate set-down would occur almost immediately beside the pushing skate. However, as seen here in dp skating, the recovery skate and center of gravity is moving away from the direction of push. The recovery leg skate is almost thrown out to the side as the body weight moves away from the pushing leg.

Frame 3:

This frame depicts the precise moment that the recovery skate touches the road. Notice that the pushing skate is about 2/3 of the way through it’s range of motion. In this manner, the set down occurs very late in dp skating when compared to classic technique. The instant that the set-down skate touches down, almost full body weight is applied to what now becomes the support leg. This is a necessary step in order to generate what will become force potential for “pulling. Notice that the skate sets-down directly on top of the wheels, but rolls onto the outside almost immediately (see last frame).

Frame 4:

In this last frame the set down skate is now on the road and rolls onto the outside edge of the wheels. The skate also turns slightly inwards towards the body to help generate pulling force and initiate the inward motion of the leg. From observing the position of the hips and shoulders, it is apparent that an increased amount of body weight is being applied to the set-down/support leg skate. Notice as well that as this transition in body weight occurs and the support leg skate begins to move inwards, the pushing leg is still moving laterally and therefore still generating propulsion. For a very brief moment, both skates are helping to conserve momentum by applying propulsive force. This leads to a smoother transition between push and pull and avoids the subtle but significant deceleration that occurs during the recovery process of classic technique.

Executing the set down mechanics described is very difficult, especially for classic skaters who are attempting to break a pattern of movement that comprise a strongly developed motor program achieved through years of skating and literally millions of strides. Experience has taught me that very few people prove able to learn the double-push as a whole. The easiest way is undoubtedly to slowly acquire and develop select characteristics of the overall process. The set-down appears to be the most crucial of these, and usually requires great practice, perseverance, and patience to learn. If you need additional instruction, the “Secrets of the Double-Push” video in the Skate Gear selection contains 10 useful drills for helping you to learn dp skating.

The Double-Push Revisited (Part 2 of 2)

Part one of this series discussed how the set-down of the recovery skate is one of the most difficult skills related to double-push skating. If the body position at set-down is not correct, it is impossible to execute the inward pulling motion of the support/glide leg.

The Pull

The biggest reason that the double-push technique is superior to classic technique is that power output can be applied during the entire stride. In classic technique, the glide phase is marked by a static body position where velocity gradually tapers until power is again applied in the next push-off. Consider the analogy of paddling a canoe. Each time the paddle is moved through the water, the canoe accelerates. As the paddle is taken out of the water in preparation for the next stroke, the canoe begins to lose speed. Once the paddle is again moved through the water, the canoe will accelerate once again. In sharp contrast to classic skating, the dynamic inward motion of the support/glide leg during double-push skating substitutes the normal glide phase with one which generates additional propulsive force. As a result, it is easier to accelerate, and easier to maintain velocity by dramatically reducing deceleration. Going back to the canoe example, the analogy would be like having two paddles where one could enter the water and stroke the instant the other finished its movement and left the water.

As mentioned, body position must be exact for the pull to work. The purpose of the set-down is to therefore prime for the pull by ensuring a body position that will allow the pulling actin to occur in a smooth and natural fashion. The following video photo sequence depicts changes in body position from the beginning of the set-down to the point where the support/pulling leg makes the transition to push.

The following video photo sequence depicts changes in body position from the terminal point of the inward pulling leg, to the precise instant the recovery skate touches the road.

Frame 1:

The instant the recovery skate touches the road, the hip (and body weight) move towards the side of the pulling leg. This is crucial! This step, combined with the outer wheel angle and slight "turning in" of the pull leg skate, initiate the inward motion of the pull leg. The instant that the skate begins to track inwards, active force can be applied to the adductor muscles of the (upper) inner leg to generate propulsion. Notice that as the pull begins, the other leg begins to recover.

Frame 2:

The hip and body weight continue to move in the direction of the support/pulling leg. (Notice that the imaginary line drawn from the hip to the skate is about 20-25 degrees from vertical). As the support leg pulls inwards, the skate angles progressively more on its outside edge. The knee of the recovery leg now begins to as the free skate goes through recovery. It is important to also note that as the support leg pulls inwards, it is also thrust forward very slightly so that the body weight is focused more on the middle-rear of the skate.

Frame 3:

The support leg has reached its most inward position where it has crossed under the midline (an imaginary vertical line drawn down from the center of the hips) and ahead of the body. The line drawn from the hip to support skate is steeper than in the previous frame i.e. 25-30 degrees. At this point, the hips and body weight remain over the support leg skate. The recovery skate has been drawn almost directly inwards as it approaches a position almost behind/beside the support leg skate.

Frame 4:

The transition to push is made as the hips and body weight begin to move back towards the recovery leg side. As this occurs, the support leg skate now begins to move in the direction of push. Note that in the early stages of the push, the skate is still oriented on the outside wheel edge. It will not "roll over" onto the inside wheel edge until it passes the vertical line drawn down from the same side hip. This happens very rapidly because as the skate moves outwards into push, the hips are already moving in the opposite direction. The recovery leg has finished regrouping, and is preparing to move out to the side as the push progresses.

Mastering the double-push takes literally years of practice and perseverance. Being able to set the skate down properly, and generate additional propulsion through the pulling action of the support leg are the most vital aspects of double-push skating. Although this technique will remain difficult to learn solely from photos and explanation, it is my hope that these articles can at least assist developing skaters in their quest for speed and efficiency.

Double-Push Skating: The Mystery Revealed

Does it really work? And why? How much faster is it? And how the heck do you do it? Ask 10 skaters and you get 10 different answers. This is what often happens when you start asking around about the double-push. Why is this? If you ask me, it's because even many of the top pro skaters, even those who are good double-push skaters, don't really understand what it is. Don't expect that just because a big-name skater can do it that they can tell you how it's done or what makes it work. It continues to baffle me why some of the top skaters in the world practice avoidance on the subject, and continue to downplay the relevance or importance of this technique. People are often afraid of things they don't understand, and no one wants to admit that they can't explain something they're good at doing.

There is no doubt (at least in my mind) that the double-push is largely responsible for the progressively faster times being seen in the US and abroad. Sure, the are more good skaters today than there were 5 years ago, and improvements in training methodology lead to fitter athletes. But I don't think these points alone can account for the way 10k pro (mens) times have dropped as much as they have i.e. under 15 minutes in some cases! In a less abrupt or dramatic way, the double-push is doing for inline what the klap skate is doing for ice. While the latter is the direct result of an equipment revolution which frees the once-restricted ankle joint, the former is simply a superior and more efficient way to propel the body forward. My interest here is to simplify the primary reason why.

Will that be one lump or two

The superiority of the double-push is that force (power output) can be applied in two separate ways. With classic technique, this is impossible. The normal glide phase is a big 'ol waste of energy. What the double-push does is finds a way to re-direct this static energy into a separate channel of propulsion. At the double-push clinics, I like to use paddling a canoe as an indirect way to highlight the benefit this can offer. When paddling, the only time you propel the boat forward is during the actual stroke. After a stroke, you have to take the paddle out of the water, move it forward, and plunge it into the water again for the next stroke. During the time it takes to prepare for the next stroke, energy is wasted and the canoe loses velocity. Now just imagine if you had two paddles, and you could stroke with the second the instant the first left the water. Now imagine that the second stroke didn't require much (if any) additional energy, but you used the energy normally spent returning the paddle to the front for the next stroke. Sound too good to be true? Well, believe it because that's exactly what double-push skating does.

Figure 1 - Classic Vs. Double-Push Technique

Figure 1 graphically illustrates the shape of the (right) skate "tracing" during one full cycle of glide/pull and push. With classic technique only one moment of force (F1) is achieved when the skater pushes away from the (relatively) straight glide path. With the double-push technique, there are 2 moments of force: F1 represents applied force as the skate is actively pulled in towards center, and F2 represents force output during the normal pushing stage. To illustrate the practical benefit of this, lets look at the example below:

Skaters A and B are both travelling 30 km/hr (18 miles/hr). Skater A, using classic technique, must apply 150 watts of power during F1 to sustain this speed. To do so, Skater A must extend the push leg from a 100 degree knee angle, achieving a push displacement to the side of 24 inches.

To sustain the same speed, Skater B (using double-push technique) must also apply the same power output i.e. 150 watts. However, because Skater B has two channels of propulsion, this output can be, 50 watts during F1, and 100 watts for F2. This means that Skater B can sit higher (e.g. 115 degrees), and divide up the same (total) push displacement into 6 inches for F1, and 18 inches for F2. If you have followed any of my articles in the past, you know that squatting low has the devastating effect of inducing early fatigue because the high muscular tension reduces blood flow. This, in turn restricts the transmission of lactic acid from the muscles into the bloodstream . Being able to sit higher using the double-push means better blood flow through the leg muscles, less fatigue, and increased efficiency.

Keep on movin' don't stop now

Have you ever left your lights on, killed the battery, and had to jump start you car? If so, then you know that the toughest part is just getting that 2000lb hunk of metal moving. Once it's going, it's relatively easy to keep it rolling. You could probably keep it rolling for 20 seconds before you expended the same amount of energy that was required just to get it going. This economy of motion is called (conservation of) momentum.

With classic skating, the glide leg (knee and hip) is held in a stationary position, supporting the entire body. Although the weight transfer helps limit the pushing effort necessary to initiate sideward movement, a considerable amount of energy is required just to get the leg going. What makes this even more difficult is the fact that the leg muscles have to contract from a biomechanically inefficient position i.e. they have been held in a static contraction for about a second.

By contrast, the double-push takes full advantage of the same principle of momentum discussed above. Because the skate/leg is already moving outward the moment that pushing force is applied, the efficiency of the weight transfer and subsequent push is greatly enhanced (it's like pushing a car that's already moving). The end result is that overall efficiency is increased because of the reduction in energy required to initiate movement.

Learning to skate double-push is a time-intensive process that often takes many months. Even so, being able to replicate the movement pattern is only half the challenge. It can take many more months until you are able to actually use it to your advantage. However, it's never too late to start.