The double pole technique is relatively simple, but like most things in the sport, is still complex enough to leave the door open to confusion, and ultimately poor technique advice. I take special attention to the idea of slamming the poles into the ground. Maybe it's just that is makes my ears bleed, but I'd like to explain why I think it undermines performance too.
The principal author of this study is Hans-Christer Holmberg of the Swedish Winter Sports Research Centre. To my knowledge, and correct me if I am wrong, no one outside of his organization is studying the biomechanics of cross country skiing to a comparative degree, nor has his findings been seriously challenged. Ironically, the only challenge has been to interpret his findings correctly in my opinion. Let’s take a closer look at his findings in his Study, Biomechanical Analysis of Double Poling in Elite Cross-Country Skiers, published by the American College of Sports Medicine in 2005. A link to this Study's paper in found under "Links" on the right.
To start, we should consider the limits of this study. First, there may be differences in the way that we double pole on rollerskis verses on real snow skis. For example, the hardness of the treadmill poling surface should be noted, as the treadmill is likely much harder than the normal poling surface in snow. Also, this study only looked at one type of terrain (flat), and at only one speed (85% of each athlete’s maximal velocity in progressive 4 minute intervals). My guess is that these conditions represent a medium to high Level 3 intensity on flat terrain with comparable speed resistance to that of snow. Nevertheless, we can still learn a lot from a small glimpse.
Forces Applied to the Poles, Forefoot and Rearfoot
Figures 1A and 1F on page 5 show the forces applied to the poles, forefoot and rearfoot, respectively, through the entire double poling cycle. In short, there is one narrow peak of force in the poles right at the plant, a decrease, then a higher and broader peak that rapidly increases then decreases more gradually until the end of the poling phase.
Forces on the feet are at their lowest in short moments right before the pole plant. The force generally increases through the poling phase, at first at the front then dramatically increases at the rear in the last 1/3 of the poling phase. The forces on the feet are the highest in the last ¼ of the poling phase and steadily decline until a rapid increase at the front about half way through the recovery phase. It is very clear that high pressure locations in the feet are very dynamic.
Muscle Sequencing
Figure 3 on page 7 shows the EMG activity of the major muscles involved for the fastest double poler in the study. There’s a lot of information there, but we do not need to spend a lot of time to notice a trend. With the exception of the smaller muscles at the ends of the arms and legs (likely to grip the poles and balance on the skis), the order of the significant muscle work begins in the lower core and works upward. The front of the lower core is very active before the pole plant, whereas the triceps do not become involved until just after the pole plant.
The lower body is quite active too. The most active include the hip flexors (included in lower core), glutes, and soleus (lower calf muscle).
Technique Correlations to Speed
Strong correlations were found between faster double poling and some technique characteristics. Correlation is on a scale of 0 to 1.
| Faster speed of elbow joint flexion (hand coming towards shoulder) during poling phase | 0.80 |
| Smaller minimum knee-angle during poling phase | 0.72 |
| Greater peak pole force | 0.70 |
| Greater peak pole force, relative to body weight | 0.66 |
Two Different Double Pole Strategies
The Study identified two different strategies, A (“wide elbow”), and B (“narrow elbow”). Strategy A was distinguished from Strategy B by having more abducted shoulder joints (wide elbows), smaller elbow angles at pole plant, faster and more distinctly flexed elbow and hip joints, and an altogether more dynamic poling phase.
Strategy A included the fastest double polers and showed these measured differences:
- Higher peak pole force, relative to body weight
- Shorter time to peak pole force (study is referring to the 2nd and broader peak)
- Higher impulse (rate of development) of pole force, relative to body weight
- High muscle activity in teres major and low to medium activity in latissimus dorsi (the lats), as opposed to medium or low activity in teres major and high activity in the lats for Strategy B.
My Thoughts
The Authors do not conclude whether these characteristics caused greater speed, or if they were byproducts of the greater speed. I will try.
Lets consider the different profiles of pole force through the poling phase of strategies A and B (Figure 1A, and shown below). It is written in the Discussion, “The first peak occurred at the impact force peak associated with the collision of the pole tip with the ground, followed by a second, higher peak, being the active force peak inducing high impulses of pole force for propulsion.” Skiers using strategy B appear to develop more force at the pole plant but end up not developing nearly the same force in the second peak. I’m going out on a short limb, but I think the former causes the latter.
The only way to increase force at the pole plant is to transfer force through the arm by tensing the triceps. This tension slows the speed of the elbow flexing during the poling phase that just so happens to be the strongest correlation to performance.
We can also note that a higher force at pole plant will necessitate a higher force through the legs in order to maintain front-to-back balance. This is because the poles are clearly in front of the center of mass at the pole plant, and any force while there, works to torque the body backwards and against what we all prefer: a forward lean. Having to transfer more force through the legs in this process prohibits flexing the knee and eventually the 2nd strongest correlation to performance: smaller minimum knee-angle during the pole phase.
Finally, these two resisted motions, elbow and knee flexion, make it very difficult to create a high and impulsive peak force, the 3rd (and 4th) strongest correlations to performance. A greater horizontal distance between the center of mass and pole increases the torque required in the trunk to achieve the same force in the pole (could that be why those using strategy B relied more on their lats muscles?). And to create the highest force possible in the pole, one must create the highest force possible in the body in the opposite direction – so says a guy named Newton. This means every part of the body, including the legs, should be accelerating (relative to the poles) in the opposite direction to the poles during the active force peak.
For these reasons, I believe that any extra force into the poles at impact undermines double pole performance. So please, keep the volume down over there.
Your Thoughts
What does this Study tell you? What do your own experiences tell you?
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