Do you have a force profile of a stroke for both techniques? It would be interesting to see max force differences and the area under the curve (total force over the stroke).
Thank you for this nice analysis of pre-activation vs a more prolonged stretch-shortening cycle (SSC) . As we can see, the same skier can choose one technique or the other, but I am left with many questions. I wonder if one is more desirable under certain circumstances? Is one technique faster (more effective) than the other? Does one conserve more energy (more efficient) than the other? Is it better to time the core/shoulder/arm muscles together or to spread them out over a longer portion of the poling cycle, and for what reasons? My sense is that the one on the left can generate more power and the one on the right perhaps more speed, but as it looks like the speed was constant on the treadmill, and the skier's perception was that he could not go any faster, perhaps not? Or, with fewer cycles over the same period of time, and the same speed, is the pre-activation method advantageous? I have felt that when we allow more flexion in elbows and shoulders after pole plant, we lose the advantage of using gravity to apply power to the poles, and transfer it to the arms. The use of the lengthened SSC could make use of the arms more effective, but isn't it overall more effective to use the core and legs, rather than the relatively smaller arm muscles? It seems the trend over the past decade or two has been to use more legs and less arms in our double poling. I know this is a lot, but I appreciate hearing your thoughts on any or all points. Thank you.
Hello, and thanks for your feedback and constructive "criticism", Jeffrey! Hope I understand your questions and there is some answers to it below. First, it depends on the circumstances, speed, terrain, skiing conditions, technique skills, strengths, and shape. However, if we compare the fastest skiers pole plant with slower skiers, they put the poles in the snow longer in front of the toe tip in all terrain. Still, they adjust the position of the pole plant to speed and level of the terrain. It is also essential to have a short time to peak force due to the inverse relationship between muscle contraction speed and the power/force produced. Without the flexion-extension pattern in the shoulder and elbow joint, we cannot preactivate and build up the tension in the muscles needed for highspeed power development. A pole plant with the poles angled too much backwords result in the arms and poles going too fast backwards and a limited force is produced to forward pulsation. So yes, we have a lot of experience and knowledge about this, and this technical solution gives the skier time to crate force, the force goes in the right direction and at the right time (TIMING). To spread the force over a longer portion of the cycle will not work since the power created in the start of the movement will go in the wrong direction (up), and the power produced at the end of the cycle becomes very small since the speed is high and increasing during the stroke. The speed at the treadmill was constant (24 km/h and 3% uphill), but before we filmed, we tested out, and this was the speed he was able to execute with the sound and his preferred technique, and when we focused on taking away the sound, he was able to do up to 27 km/h. When we concentrate on the sound, it clearly reduced the impact forces and reduced the "clash" between poles and underlayer, and it brought forward a distinct flexion-extension pattern and preactivation of the muscles that are doing the poling stroke, and this is the strategy used by elite class skiers. The use of stretch-shortening strategy in arm and shoulder also depends on the fall in the whole body and the ability to translate bodyweight onto the poles and maintain the body weight on the pole through the first part of the cycle, timely avoiding "sitting down" style. In this context, it is essential to use the abdominal muscles and not the hip flexors (rectus femoris and Iliopsoas) too early in the cycle to avoid too much up and down movement. Too much up and down movement in legs, often results in a waste of energy in vertical displacement of the centre of body mass instead of forward pulsation (less use of the legs). Reg. Per-Øyvind
@@cross-countryskiingper-yvi9028 Thanks for your thoughtful in-depth reply! There's a lot of really good information here, and I'm glad to see that it is consistent with what I have been thinking and/or coaching. I also am glad to see the concept of reducing the initial impact forces with the ground, making the pole plant quieter, as I feel, as a Physical Therapist, that this will be better for the longevity of skiers' wrist, elbow and shoulder joints and tendons. This will be a helpful cue for teaching good technique. One of the reasons that I had sought clarification was that one of your previous videos (th-cam.com/video/-z_R2jgsZns/w-d-xo.html) had been interpreted by some fellow skiers to suggest that the pattern on the right of this video was the more desirable technique. We do see some of the top skiers use this movement pattern at certain times during the race... perhaps most notably during sprints (?). I am left to wonder if this is done through desperate attempts to sprint faster, and/or if it is done when either the arm muscles are too fatigued to provide proper stabilization, or if the muscles that are used to perform the more appropriate technique are fatigued, so the athlete shifts to other, less fatigued muscles. Or perhaps it is a conscious choice because it in some ways feels faster, as some of my fellow skiers have suggested. There is so much to learn through research, and I thank you for being part of the answer-seeking enterprise.
@@jeffreyrussell8694 Hello Jeffery! Prisiate your comments and perspectives! My experience is comes from work with the Norwegian national sprint team for 5 years, coaching a lot of World class Skiers, and lately working and reaceaching on Long Distance World class Visma Ski Classic skiers and all of them have a distingth flextion-extention patten in the sholder and elbow or we have tryed to implement this in their technique. It is very useful if the speed is high, or if it is a sprint against the finish Line (actually a prerequist for moving that fast). However, it is also a preferanser technique just to «transport» the skier in the long distance races and it is a often replaced the «high hel-high hip» and forward shift of the center of body mass strategy to reduce the energycost. It is also quit clear to me that that the eccentric preactivation is impresivly effective bouth in relation to execute force in high speed and produce high force pr.se. As I have pointed out earlier it is only in the uphills I think the skiers can double pole with a pole more angled backwords and create force directly after the pole plant. Stil, many skiers are performance a SSC even in the uphills. The reason for that some skiers are not using this strategy is due to what the coaches are trying to learn them. I know a lot of coaches that dont agree with me and their currant thinking is that the skier are to wek in the arm muscles to stabilice the sholder and elbow joint. There is also a misunderstanding from the translation of the biomecanic to practice . Where the understanding that the force is highest in the start of the movement ( resulting in high poleplant force) whitout understanding of the effect is dependent on the poleangle when the force is highest. Sorry for my englich in this answer hope it was understandable? PØT
@@cross-countryskiingper-yvi9028 Thanks for your reply, Per, This is certainly an intriguing topic, and one that should help guide us to improved performance if we interpret things correctly. I am in agreement that the flexion-extension pattern of the upper limbs during double poling is an important contributing factor to effective performance, however, Zoppirolli, Holmberg, Pelligrini et al (The Effectiveness of the stretch-shortening cycling in upper limb extensor muscles during elite cross-country skiing with the double poling technique, Journal of Electromyography and Kinesiology 2013) concluded that it was the increased EMG, or muscle activation, creating muscle stiffness that was the key element during this phase of movement of the faster skiers. With increased stiffness prior to and at pole plant, one would expect a reduction in the shoulder and elbow flexion angles, relative to a skier with reduced muscle pre-activation. Additionaly, Zoppirolli, Bertolan, Schena and Pellegrini found that the higher the elongation of duty cycle, defined as the portion of the poling phase with poles in the snow, the higher the cycle length and velocity decrement. (Double Poling kinematic changes during the course of a long-distance race: effect of level of performance, Journal of Sports Sciences vol 38, No 8, 2020). This was attributed to a fatigue factor over the course of a long-distance race, so it may not be fair to extrapolate it to technique alone, but the ability to create and maintain powerful force early in the poling cycle would seem advantageous. If the elbow and shoulder joints flex excessively at pole plant, this would reduce the ability to create force early in the poling cycle. We also do not want to neglect the contribution of the legs to the ability to generate force and speed in double poling, as it is the drop of the body's weight onto the poles, using gravitational potential energy rather than direct muscular kinetic energy that enables high force production. Using the legs to combine forward movement of the center of mass with a high position from which to drop onto the poles would seem to be significant to the ability to optimize velocity. I would be interested in your thoughts and any alternative interpretations. Respectfully, Jeff R
Hello Jeff, :-) I am thankful for your comments, excellent insight into the literature, and knowledge of skiing techniques. Remarkably interesting to read your perspective. However, it all comes down to the timing of the force (and we are now discussing the details), and if we should follow the principle of early activation to create greater force in double poling, we must be were of the angle of the poles. If the poles are put into the ground in a vertical position (which is a preferred strategy of the best skiers in high speed), the response from the poles will also create an opposite force in a vertical direction if we use high force early in the cycle, and this is not effective since we create high collision forces and destroyed the poles an underlayer. However, if we use the bodyweight on the poles and starts the movement with a stretch-shortening cycle in the shoulder and elbow, the poles will come into a favourable angle when the upper arms start to do the arm stroke followed by the underarm. However, if we are in an uphill, this seems to be different, and the skier is locking the shoulder and elbow joint, having the arms and poles quite close to their body and putting the poles much more angled backwards can activate high force immediately. The legs are used to pump the skier up and reposition the skier into the next stroke, and we see a much more active stomach and upper bodywork and lessarms in use. I think the differences in speed and terrain need adjustments of the technique to each skier's capacity (endurance and strength). Ski reg PØT
Great comparison. Have you looked at force profiles of both techniques? With the technique on the right, you have distinct force peak (in the beginning of the stroke). So, with the modified technique, the force is more evenly distributed over the stroke?
Right. I think you are referring to the initial, brief spike of force at pole plant, followed by a reduction in force before the majority of the force/time curve develops. One would expect that a technique that generates a higher speed, with fewer poling cycles, would be the preferred one, at least as far as effectiveness is concerned, as the higher speed is really the desired outcome. That initial spike in force has such a rapid development that it would be a shock to the joints, whereas the modified technique (without the spike) ramps the force up a bit more progressively and thus more gently to the athlete's body. We use the same cue to reduce initial impact force for runners and jumpers.
Hello Ales! Thanks fore commenting on this. I havent measure this but HC HOLMBERG described this in 2005 when he analyses the doublepoling technique and I think you can find a video on TH-cam «Debunking the myth of double poling» about it. The result from the reseach showes a higher but a bit latter force with (the highest force comes when the poles are in a optimal Angle to the ground and to optimice forward pulsation) high effect on forward pulsation in the sound modified technique!
I've tuned mechanical systems like trebuchets before as a hobby and there are some immediate takeaways. It looks like most of the energy in the stroke is initially stored as potential energy when the skier stands up. It must then be converted into forward motion when he poles. In the first one (loud), his arms bend on initial contact because the forces are too great (this is wasteful). More worrying, his center of mass (CM) moves downward rapidly before being abruptly stopped by his leg muscles and back (failing to use this energy). In the second (silent), there is very little arm bending and the downward CM motion seems to be stopped more naturally during the polling motion*. This indicates a much more efficient stroke. *I think that the positions of the arms and polls near the bottom of the CM motion are what matters. Trying to hit an optimal angle pole position on first contact is pointless, as most of the stroke's energy is still potential energy. In contrast, the seemingly senseless very forward initial pole plant looks like a mnemonic for getting a good late stroke position.
Hi, if I compare the technique from this video (about half way in) th-cam.com/video/hg0b03fr4mg/w-d-xo.html to this skier, I can see that here the person is not leaning or coming down on their poles. Instead it seems they are kinda just moving up and down with almost no fall at all. Is that because they are going really fast or on roller skis? As a person who is new to this sport I'm trying to figure out why. Thanks!
Thank you very much for this exciting and well-explained content!!!
Good analysis!
Thanks, Bjørn!
Excellent. Thank you.
Thanks Tyler!
Do you have a force profile of a stroke for both techniques? It would be interesting to see max force differences and the area under the curve (total force over the stroke).
Thank you for this nice analysis of pre-activation vs a more prolonged stretch-shortening cycle (SSC) . As we can see, the same skier can choose one technique or the other, but I am left with many questions. I wonder if one is more desirable under certain circumstances? Is one technique faster (more effective) than the other? Does one conserve more energy (more efficient) than the other? Is it better to time the core/shoulder/arm muscles together or to spread them out over a longer portion of the poling cycle, and for what reasons? My sense is that the one on the left can generate more power and the one on the right perhaps more speed, but as it looks like the speed was constant on the treadmill, and the skier's perception was that he could not go any faster, perhaps not? Or, with fewer cycles over the same period of time, and the same speed, is the pre-activation method advantageous? I have felt that when we allow more flexion in elbows and shoulders after pole plant, we lose the advantage of using gravity to apply power to the poles, and transfer it to the arms. The use of the lengthened SSC could make use of the arms more effective, but isn't it overall more effective to use the core and legs, rather than the relatively smaller arm muscles? It seems the trend over the past decade or two has been to use more legs and less arms in our double poling. I know this is a lot, but I appreciate hearing your thoughts on any or all points. Thank you.
Hello, and thanks for your feedback and constructive "criticism", Jeffrey! Hope I understand your questions and there is some answers to it below.
First, it depends on the circumstances, speed, terrain, skiing conditions, technique skills, strengths, and shape. However, if we compare the fastest skiers pole plant with slower skiers, they put the poles in the snow longer in front of the toe tip in all terrain. Still, they adjust the position of the pole plant to speed and level of the terrain.
It is also essential to have a short time to peak force due to the inverse relationship between muscle contraction speed and the power/force produced. Without the flexion-extension pattern in the shoulder and elbow joint, we cannot preactivate and build up the tension in the muscles needed for highspeed power development. A pole plant with the poles angled too much backwords result in the arms and poles going too fast backwards and a limited force is produced to forward pulsation. So yes, we have a lot of experience and knowledge about this, and this technical solution gives the skier time to crate force, the force goes in the right direction and at the right time (TIMING). To spread the force over a longer portion of the cycle will not work since the power created in the start of the movement will go in the wrong direction (up), and the power produced at the end of the cycle becomes very small since the speed is high and increasing during the stroke.
The speed at the treadmill was constant (24 km/h and 3% uphill), but before we filmed, we tested out, and this was the speed he was able to execute with the sound and his preferred technique, and when we focused on taking away the sound, he was able to do up to 27 km/h. When we concentrate on the sound, it clearly reduced the impact forces and reduced the "clash" between poles and underlayer, and it brought forward a distinct flexion-extension pattern and preactivation of the muscles that are doing the poling stroke, and this is the strategy used by elite class skiers. The use of stretch-shortening strategy in arm and shoulder also depends on the fall in the whole body and the ability to translate bodyweight onto the poles and maintain the body weight on the pole through the first part of the cycle, timely avoiding "sitting down" style. In this context, it is essential to use the abdominal muscles and not the hip flexors (rectus femoris and Iliopsoas) too early in the cycle to avoid too much up and down movement. Too much up and down movement in legs, often results in a waste of energy in vertical displacement of the centre of body mass instead of forward pulsation (less use of the legs).
Reg. Per-Øyvind
@@cross-countryskiingper-yvi9028 Thanks for your thoughtful in-depth reply! There's a lot of really good information here, and I'm glad to see that it is consistent with what I have been thinking and/or coaching. I also am glad to see the concept of reducing the initial impact forces with the ground, making the pole plant quieter, as I feel, as a Physical Therapist, that this will be better for the longevity of skiers' wrist, elbow and shoulder joints and tendons. This will be a helpful cue for teaching good technique.
One of the reasons that I had sought clarification was that one of your previous videos (th-cam.com/video/-z_R2jgsZns/w-d-xo.html) had been interpreted by some fellow skiers to suggest that the pattern on the right of this video was the more desirable technique. We do see some of the top skiers use this movement pattern at certain times during the race... perhaps most notably during sprints (?). I am left to wonder if this is done through desperate attempts to sprint faster, and/or if it is done when either the arm muscles are too fatigued to provide proper stabilization, or if the muscles that are used to perform the more appropriate technique are fatigued, so the athlete shifts to other, less fatigued muscles. Or perhaps it is a conscious choice because it in some ways feels faster, as some of my fellow skiers have suggested. There is so much to learn through research, and I thank you for being part of the answer-seeking enterprise.
@@jeffreyrussell8694 Hello Jeffery! Prisiate your comments and perspectives! My experience is comes from work with the Norwegian national sprint team for 5 years, coaching a lot of World class Skiers, and lately working and reaceaching on Long Distance World class Visma Ski Classic skiers and all of them have a distingth flextion-extention patten in the sholder and elbow or we have tryed to implement this in their technique. It is very useful if the speed is high, or if it is a sprint against the finish Line (actually a prerequist for moving that fast). However, it is also a preferanser technique just to «transport» the skier in the long distance races and it is a often replaced the «high hel-high hip» and forward shift of the center of body mass strategy to reduce the energycost. It is also quit clear to me that that the eccentric preactivation is impresivly effective bouth in relation to execute force in high speed and produce high force pr.se. As I have pointed out earlier it is only in the uphills I think the skiers can double pole with a pole more angled backwords and create force directly after the pole plant. Stil, many skiers are performance a SSC even in the uphills. The reason for that some skiers are not using this strategy is due to what the coaches are trying to learn them. I know a lot of coaches that dont agree with me and their currant thinking is that the skier are to wek in the arm muscles to stabilice the sholder and elbow joint. There is also a misunderstanding from the translation of the biomecanic to practice . Where the understanding that the force is highest in the start of the movement ( resulting in high poleplant force) whitout understanding of the effect is dependent on the poleangle when the force is highest.
Sorry for my englich in this answer hope it was understandable?
PØT
@@cross-countryskiingper-yvi9028 Thanks for your reply, Per, This is certainly an intriguing topic, and one that should help guide us to improved performance if we interpret things correctly. I am in agreement that the flexion-extension pattern of the upper limbs during double poling is an important contributing factor to effective performance, however, Zoppirolli, Holmberg, Pelligrini et al (The Effectiveness of the stretch-shortening cycling in upper limb extensor muscles during elite cross-country skiing with the double poling technique, Journal of Electromyography and Kinesiology 2013) concluded that it was the increased EMG, or muscle activation, creating muscle stiffness that was the key element during this phase of movement of the faster skiers. With increased stiffness prior to and at pole plant, one would expect a reduction in the shoulder and elbow flexion angles, relative to a skier with reduced muscle pre-activation. Additionaly, Zoppirolli, Bertolan, Schena and Pellegrini found that the higher the elongation of duty cycle, defined as the portion of the poling phase with poles in the snow, the higher the cycle length and velocity decrement. (Double Poling kinematic changes during the course of a long-distance race: effect of level of performance, Journal of Sports Sciences vol 38, No 8, 2020). This was attributed to a fatigue factor over the course of a long-distance race, so it may not be fair to extrapolate it to technique alone, but the ability to create and maintain powerful force early in the poling cycle would seem advantageous. If the elbow and shoulder joints flex excessively at pole plant, this would reduce the ability to create force early in the poling cycle.
We also do not want to neglect the contribution of the legs to the ability to generate force and speed in double poling, as it is the drop of the body's weight onto the poles, using gravitational potential energy rather than direct muscular kinetic energy that enables high force production. Using the legs to combine forward movement of the center of mass with a high position from which to drop onto the poles would seem to be significant to the ability to optimize velocity. I would be interested in your thoughts and any alternative interpretations. Respectfully, Jeff R
Hello Jeff, :-)
I am thankful for your comments, excellent insight into the literature, and knowledge of skiing techniques. Remarkably interesting to read your perspective. However, it all comes down to the timing of the force (and we are now discussing the details), and if we should follow the principle of early activation to create greater force in double poling, we must be were of the angle of the poles. If the poles are put into the ground in a vertical position (which is a preferred strategy of the best skiers in high speed), the response from the poles will also create an opposite force in a vertical direction if we use high force early in the cycle, and this is not effective since we create high collision forces and destroyed the poles an underlayer. However, if we use the bodyweight on the poles and starts the movement with a stretch-shortening cycle in the shoulder and elbow, the poles will come into a favourable angle when the upper arms start to do the arm stroke followed by the underarm. However, if we are in an uphill, this seems to be different, and the skier is locking the shoulder and elbow joint, having the arms and poles quite close to their body and putting the poles much more angled backwards can activate high force immediately. The legs are used to pump the skier up and reposition the skier into the next stroke, and we see a much more active stomach and upper bodywork and lessarms in use. I think the differences in speed and terrain need adjustments of the technique to each skier's capacity (endurance and strength).
Ski reg PØT
Great comparison.
Have you looked at force profiles of both techniques? With the technique on the right, you have distinct force peak (in the beginning of the stroke). So, with the modified technique, the force is more evenly distributed over the stroke?
Right. I think you are referring to the initial, brief spike of force at pole plant, followed by a reduction in force before the majority of the force/time curve develops. One would expect that a technique that generates a higher speed, with fewer poling cycles, would be the preferred one, at least as far as effectiveness is concerned, as the higher speed is really the desired outcome. That initial spike in force has such a rapid development that it would be a shock to the joints, whereas the modified technique (without the spike) ramps the force up a bit more progressively and thus more gently to the athlete's body. We use the same cue to reduce initial impact force for runners and jumpers.
Hello Ales! Thanks fore commenting on this. I havent measure this but HC HOLMBERG described this in 2005 when he analyses the doublepoling technique and I think you can find a video on TH-cam «Debunking the myth of double poling» about it. The result from the reseach showes a higher but a bit latter force with (the highest force comes when the poles are in a optimal Angle to the ground and to optimice forward pulsation) high effect on forward pulsation in the sound modified technique!
I've tuned mechanical systems like trebuchets before as a hobby and there are some immediate takeaways.
It looks like most of the energy in the stroke is initially stored as potential energy when the skier stands up. It must then be converted into forward motion when he poles.
In the first one (loud), his arms bend on initial contact because the forces are too great (this is wasteful). More worrying, his center of mass (CM) moves downward rapidly before being abruptly stopped by his leg muscles and back (failing to use this energy).
In the second (silent), there is very little arm bending and the downward CM motion seems to be stopped more naturally during the polling motion*. This indicates a much more efficient stroke.
*I think that the positions of the arms and polls near the bottom of the CM motion are what matters. Trying to hit an optimal angle pole position on first contact is pointless, as most of the stroke's energy is still potential energy. In contrast, the seemingly senseless very forward initial pole plant looks like a mnemonic for getting a good late stroke position.
Thanks for your contribution and for complementary my key points :-)
👏👏
Hi, if I compare the technique from this video (about half way in) th-cam.com/video/hg0b03fr4mg/w-d-xo.html to this skier, I can see that here the person is not leaning or coming down on their poles. Instead it seems they are kinda just moving up and down with almost no fall at all. Is that because they are going really fast or on roller skis? As a person who is new to this sport I'm trying to figure out why. Thanks!