Watts in the Poles – What Does It Take to Be a Cross-Country Skier? A Meta-Analysis of the Swedish Ski Federation’s Performance Requirements

Watts in the Poles – What Does It Take to Be a Cross-Country Skier?

A Meta-Analysis of the Swedish Ski Federation’s Performance Profile

Dan Kuylenstierna

There are still not many of the world’s cross-country skiers who train and compete daily with a power meter, but slowly an awareness is beginning to spread. This is evidenced, among others, by Edvin Anger1, and even Jens Burman has taken notice of it during cycling sessions2. At Skisens, we’re very pleased to see this growing awareness about watts, since understanding a metric is the first step to being able to use it. As a user, the most important knowledge is not primarily how it is measured, but how to interpret the result. Step one is understanding what constitutes a good number and what is a less competitive number in relation to one’s own ambitions. In parallel with developing the measurement tools, we at Skisens are therefore working extensively to build this knowledge base.

We have previously written about what elite skiers and recreational skiers achieve in watts per kilogram over different work durations in double poling3. One challenge, however, is that watts/kg also varies depending on terrain and speed. A recently conducted study established that there is a large difference in watts/kg on flat terrain compared to steep inclines4. In particular, the study showed very large differences when it comes to short work durations (<60 seconds). The reasons for these differences include the body’s ability to empty its anaerobic reserves more easily when working against greater resistance. Another reason is that the body’s gross efficiency varies with incline and speed5. In addition to terrain and incline, gross efficiency is also affected by technique. When the incline becomes steeper, it is advantageous for most skiers to switch from double poling to diagonal technique. In fact, gross efficiency has been studied significantly more for diagonal skiing than for double poling. Several such studies are summarized in the Swedish Ski Federation’s performance profile, which is a comprehensive compilation published on their website6.

In this text, we dive deeper into the federation’s performance profile by converting VO2 and gross efficiency into external power, which is then related to our own tests and measurements of skiers at different levels. Table 1, which is borrowed from the federation’s performance profile6, summarizes key values for female and male skiers at national top level and world elite level in distance disciplines. Based on oxygen uptake, efficiency, and utilization at 2 mmol/l, we find that women and men at senior level are at approximately 3.3 watts/kg and 3.8 watts/kg respectively, while corresponding values for juniors are around 3.2 watts/kg and 3.4 watts/kg. A brief reflection on this is that junior women are closer to the senior elite than junior men of the same age, which is not surprising since women generally develop earlier. The same pattern is seen at a load of 4 mmol/l, where seniors measure approximately 3.7 watts/kg and 4.4 watts/kg, and juniors about 3.6 watts/kg and 4.0 watts/kg. One uncertainty in the calculations above is that efficiency and utilization generally vary with speed and incline. In these cases, they were extracted at a fixed load of 5 degrees/9 kph for women and 6 degrees/10 kph for men, which aligns well with the 2 mmol threshold.

Table 1: Key values for female and male distance skiers at junior and senior elite level. The table is borrowed from the Swedish Ski Federation’s performance profile1.

The federation’s performance profile also presents speed and incline at respective thresholds—see Table 2. Based on treadmill speed and incline, external power can be calculated directly without involving efficiency, provided that friction is known. In an underlying study, friction was measured at µ = 0.0247. Using this value, we can calculate external power from Table 2 according to Table 3. Notably, these values are slightly higher than the numbers calculated earlier. One explanation could be that the sample groups differ somewhat. Table 1 refers to the Top 30 in WC >3 times, while Table 2 refers to International top level and International elite, and the relationship between these is unclear.

Table 2. Speed and incline at 2 mmol/l and 4 mmol/l for women and men at different performance levels, Table 14 in SSF’s performance profile.

Table 3. Incline and treadmill speed converted to watts per kg for men and women at different performance levels.

To put the values above into context, it can be mentioned that the 2 mmol/l threshold roughly corresponds to what in cycling is referred to as “functional threshold power (FTP)” or “critical power (CP)”, which in terms of performance equates to the power a skier can sustain for one hour. Furthermore, the 4 mmol/l value often lies close to what is referred to as “peak 20-minute power”. These statements are partly controversial compared to common assumptions. Most people tend to refer to 4 mmol/l as FTP, but in that case one cannot use the 4 mmol/l threshold or OBLA, as it is also called, from a step test like the one above. Lactate values measured in step tests tend to overestimate FTP and are also sensitive to the protocol used. From the underlying study, it appears that the values in Table 2 were collected with a protocol starting at 3 degrees and 8 kph for women and 4 degrees and 9 kph for men. Each level lasted 4 minutes with 1 minute rest between levels. The step increase between levels was 0.5 kph and 1 degree. With a different protocol, the thresholds might have been different. Support for this can be found in the literature. In a study of 10 women at national top level8, gross efficiency at 4 mmol/l was determined to be 17.8±1%, corresponding to an external power of 3.3±0.3 watts/kg.

Taken together, we conclude that women in the world elite in distance skiing using diagonal technique should have an FTP > 3.3 watts/kg and a 20-minute peak power around 10% higher. For men, FTP should be > 3.7 watts/kg, while 20-minute peak power should exceed 4.2 watts/kg.

Before concluding, it should be emphasized that the figures discussed above from the federation’s performance profile apply exclusively to diagonal skiing. In double poling or skating, efficiency and utilization differ, so values vary. However, it is worth noting that a 20-minute peak power above 4.2 watts/kg aligns well with what we have measured in strong double poling athletes.

In SSF’s performance profile, there is no data on watts/kg in double poling on a treadmill, but there is data for juniors on a 1000-meter SkiErg test. There we see that the top 15 women and men measure 191 watts and 341 watts respectively. The document contains no direct information about body weight, but indirectly, based on conditioning values (ml/kg/min) and oxygen uptake volume (l/min) in Table 1, we can estimate an average body weight and conclude that women average about 3.1 watts/kg and men about 4.4 watts/kg.

How efficiency and utilization vary with speed and incline in different sub-techniques is still partly unexplored. Furthermore, it is largely unknown how power output behaves over shorter time periods where anaerobic work plays a bigger role.

References

  1. Cross-Country Skiing: Edvin Anger on His Unique Physique: “More Watts in the Poles” | SVT Sport
  2. Påsk & Första Löptävlingen För I År
  3. Finding the Stroke in Double Poling with Skisens | SKISENS
  4. Marton Horvat et al., “Incline-dependency of the power-duration relationship in cross-country skiing”
  5. Sandbakk, Øyvind et al., European Journal of Applied Physiology (2012)
  6. SSF_Kravprofil_A4_WEBB_uppslag.pdf
  7. Jones, Thomas et al., “Anthropometric, physiological, and performance developments in cross-country skiers.” Medicine & Science in Sports & Exercise 53.12 (2021): 2553-2564.
  8. Carlsson, Magnus et al., The Journal of Strength & Conditioning Research (2016)
  9. Skiba, Philip Friere et al., International Journal of Sports Physiology and Performance (2021)