Power in Cross-Country Skiing – How Should Watt Be Interpreted Compared to Cycling?

When we started developing our power meter, we were naturally inspired by cycling, where external power – commonly referred to through the unit watt – is an established standard for measuring performance and guiding training. It has taken almost ten years to reach the point where we can now launch our product commercially and connect our sensors to established sports watches.

Along the way, we have not only faced technical challenges, but also many interesting and more fundamental questions. Perhaps the most important one is how watts should actually be interpreted in cross-country skiing. Can it be understood in the same way as in cycling, or does it require a different approach? The answer is naturally that we need to think somewhat differently; no sport is entirely like another. But fundamentally, by generalizing the concept of power, we can use the same tools as in cycling. Now that our technology is commercially available, we will publish a series of articles during the winter to help you interpret our metrics within the same framework that is established in cycling.

Why Watt Works So Well in Cycling

The reason watt works so well for cycling is that the body’s efficiency while cycling is relatively independent of external conditions such as gradient and speed. This means that the internal physiological load largely follows the external power measured in watts. After power meters became widely adopted in cycling, more sports have followed. Perhaps the most well-known example is running power, which is now commercially established, though without the same impact that watt measurement has had in cycling.

The reason watt works well for cycling but is more difficult to interpret in running is that during running on flat terrain, the body in practice does not generate any significant external work, and external power is therefore close to nonexistent. For a deeper discussion, we refer to our recently published “White Paper – A Hybrid First-Principles Model for Understanding Running Energetics on Flat and Inclined Terrain”.

Figure 1: Normalized pole power (NPP) compared to external power, heart rate, and lactate during an incremental diagonal skiing treadmill test. Note how NPP on average follows the external power required to maintain position on the treadmill. Variations occur because the skier moves slightly back and forth on the belt and because the contribution from legs and arms varies somewhat between pole strokes.

Power in Cross-Country Skiing – Similarities and Differences Compared to Running and Cycling

Skiing resembles cycling in many ways more than running, since the body continuously performs work to overcome friction. This makes watts relevant for skiing, unlike running. A challenge, however, is that the body’s efficiency in skiing varies more with external conditions. This means that external power should not immediately be used for intensity control. Nor can performance be compared directly using watts or watts per kilogram without considering the terrain where the value was recorded.

For those accustomed to watts from cycling, this makes the situation somewhat more difficult to interpret due to larger variations in efficiency. The same principle can however also be found in cycling: few cyclists can produce the same watts on flat terrain as uphill. It is also well known that a session with uneven load rarely yields the same average power as a session with steady power. To handle this, cyclists often apply so-called normalized power (NP), which compensates for variations in intensity.

Normalized Pole Power (NPP) – A Metric for Intensity Control

Within skiing, we at Skisens have introduced normalized pole power (NPP) as a metric for intensity control. Unlike external power, which as described above varies with external conditions, NPP follows the body’s internal load and is therefore well suited for defining training zones and guiding intensity. NPP can also be used to monitor development of capacity – your power profile, estimated from NPP, is a measure of your performance capacity in different types of terrain.

Further Reading: White Papers and Research

For a deeper understanding of NPP and power in cross-country skiing, we refer to our latest White Paper “Energetics, Power and Gross Efficiency in Cross-Country Skiing” as well as our earlier article from last spring: “Internal Load, External Load and Pole Efficiency Index (PEI) in Cross-Country Skiing”. Based on the frameworks presented in these articles, it becomes clear that power in skiing, besides being somewhat more complex to interpret than in cycling, also tends to be even more useful when connected to terrain variation, as it then provides insights into technical qualities and strengths.

Summary

In the articles referenced above, we share the collective knowledge required to truly understand what power means in practice – within cross-country skiing and also running. With NPP and our tools, shaped by decades of experience from the cycling world and a decade of development specifically for skiing, we want to make this insight alive and useful for all of you striving to take the next step in your development. Whether you are chasing a personal best in the tracks, pushing yourself in running, or simply wanting to get more out of every training session, we are with you all the way toward your full potential.