Why You Should Measure Power in the Field – Three Graphs That Tell the Story

Just 2 km from my home, there is a hill that climbs 35 vertical meters over 700 meters. For those familiar with the Gothenburg area, it’s the climb from Mölnlycke Företagspark up to Hultet. The start is by the bus stop next to the restaurant Solsidan, and the finish is at the bus stop at the top of Hultet.
Many of us cross-country skiers use this hill for training sessions and to test our climbing capacity.

Lately, I’ve been using this hill to validate the Skisens power grips. The gradient is consistent enough that we can compute mechanical work and power output based on friction and slope. One uncertainty factor is wind, as well as how friction changes with temperature and weather. To account for this, I always note wind speed, temperature, and whether the pavement is wet or dry.

Below are two graphs that clearly illustrate how incredibly valuable power measurement is when comparing performance under varying outdoor conditions.

Field Test: How Power Reacts to Changing Conditions

Figure 1 shows data from Today’s Plan during a session last week where I skied the hill at three different intensities (approx. A1, A2, and A3) with tailwind and roughly 18°C.

Figure 2 shows the exact same test from yesterday, but this time with headwind and similar temperatures.

Despite the headwind, the results are striking:

Each interval was 14–17 seconds slower in the headwind

BUT power output remained nearly identical

In the first two intervals, power was even slightly higher in the headwind despite slower times

In the final interval, the power difference between tailwind and headwind was within 2%, confirming high measurement reliability

Time fluctuated heavily; power did not.

These two graphs alone prove why power is the only reliable metric in cross-country skiing when external conditions vary.
On snow, where glide friction changes far more dramatically, power becomes even more essential.

Skierg vs. Field Power – What Can We Learn?

To highlight the value of power even further, I replicated the same interval structure on a Skierg.
Figure 3 shows power and heart rate for three 700 m intervals with 2 minutes rest — chosen to match the hill intervals.

Since I completed these right after the outdoor test, I was fully warmed up.

The goal was to see:

How Skierg power compares to real on-snow or roller-ski power

How field power data complements indoor training

Whether technique limitations show up in the comparison

From Figure 3 we can conclude:

Power in the first two intervals was slightly lower on the Skierg than outdoors

Likely because I pushed a bit harder outdoors

In the final near-max interval, Skierg power was almost 20% higher

This shows that technique limits outdoor power — you cannot transfer 100% of your muscular work into forward propulsion

Skisens’ hypothesis:

Elite skiers transfer power much more efficiently outdoors

Less experienced skiers lose more power to poor technique

Our early tests confirm this.

The Skierg is excellent for building capacity —
but if you never see improvements outdoors, you likely need more technique-focused ski or roller-ski training.