/ The Secret of Running

NN Egmond Half Marathon: the impact of the wind and Air Power

More 10,000 runners participated in the NN Egmond Half Marathon, which featured brutal Beaufort Force 6 winds during a 7-kilometer stretch of beach towards the city of Castricum. By running in a close pack, the elite athletes decided to waste as little power as possible by keeping each other out of the wind. Their race only started in the dunes when the pace began to rapidly pick up.

From this kind of race condition with Beaufort Force 6 winds, we can learn a lot about how winds impact your running performance by studying Stryd's power and Air Power data. In this article, we have some running tips for everybody in this article and our book, The Secret of Running.

In a closed pack, the runners battled against Beaufort Force 6 winds on the beach of Egmond in the direction of Castricum.

An example from the race: Niels Morpey


58-year-old runner Niels Morpey ran the NN Egmond Half Marathon with a new Stryd (with wind port). Niels was so kind to provide us his .fit file with running data for analysis.

“Once in the dunes, I could easily run my own speed. On the beach, this was impossible. Unfortunately, I started in the back of a group that was somewhat slow for me. In this group of about 20 runners I could often hide behind someone else, but not all the time. Also, I ran short parts in front of the group.", Niels explained.

Was it really so bad to start at the back of the pack?

While most runners would prefer to avoid the back of the pack, we think that this is not bad at all because running in a pack is a must in these running circumstances.

In the table below, we have summarized the averaged data from Niels' performance and included the course map. Until the turning point at 7 kilometers, the runners battled a fierce wind running on the beach at low tide. After leaving the beach, the track went through the sand dunes with many undulations.

How significant was the Air Resistance?

We have loaded Niels' activity file into the Golden Cheetah analysis program to view the Air Power wattage that Niels (66 kg) needed to overcome the wind.

During the first 7 kilometers, his Air Power averaged around 40 Watts, with peaks of 70 Watts and more. From the 19-K point onwards, Niels faced a crosswind which cost him around 20 Watts of Air Power.

Run at a constant power output

In our past articles and in our book The Secret of Running, we have explained that a constant power output is key for optimal performance. That is why you need to run slower uphill and faster downhill. The same principle applies to the wind. Facing a headwind, you need to run slower and shield yourself as much as possible in a group. With a tailwind, you need to run faster.

The graph below shows the total power and the Air Power from Niels' run. The first kilometer was downhill and, as he said, Niels could not run his own pace. From the 2 K-point onwards his total power was around 270 watts. He managed to maintain this wattage throughout the race with a slight increase during the final kilometer to the finish.

Well done, Niels!

Run slower against a headwind and faster with a tailwind

On the beach, Niels required a significant amount of power to overcome air resistance. Consequently, as you will see in the next graph, his pace slowed.

- On the hard beach with significant air resistance, Niels' pace was near 5:00/km.
- In the dunes with the same power, his pace sped up to 4:20/km.
- Near the finish, Niels sprinted at 4:05/km.
- On average, his pace was 4:33/km.
- Finishing time: 1:36:28.

In the y-axis of the next figure,  you will see what percentage of total power was needed to surmount the wind. We show his running velocity on the same scale (in km/h). On the beach 12 km/h. In the dunes almost 14 km/h and in the final sprint around 15 km/h.

How much time was lost due to the wind?

Niels finished in 1:36:28. He averaged 270 watts.

What would Niels's time have been in ideal conditions with no wind and a hard and even road?

In a previous article, we showed how you can calculate the finish time for a certain wattage. In the case of Niels (half marathon, 66 kg, 270 watts) his time would have been 01:29:24.

Consequently, for Niels, the Egmond half marathon turned out to be 7 minutes slower than a half marathon in ideal conditions.

How much of an advantage did Neils receive from running in the pack?


Due to the wind, Niels lost about 40 watts on the beach. The question is: how much did Niels benefit from running in the pack there?

The wind direction was southwest, at around 40° angle against the runners, with an average wind speed of 12.2 m/s, wind force 6.

With our running model, we have calculated that in these conditions 84 watts is required to overcome the air resistance.

Thanks to the Stryd foot pod we know that on average Niels needed around 40 Watts. Consequently, the average Air Power was 52% less than theory. The difference can largely be explained from the advantage of running in the pack.

In cycling similar percentages are known from riding in a pack. Of course the wind speed may also have been higher or lower at times. Finally, we draw your attention to the outliers above 70 Watts in the graph, which in our opinion show the moments when Niels ran in front of the group. At these moments he did not have the advantage of the pack, so his Air Power was near the theoretical calculations.

All in all, we believe this case is a near-perfect example of the validity of the concept of Air Power and the usefulness of the Stryd in these conditions. We conclude with a final remark from runner Niels himself: “it is almost unbelievable how accurate and useful Stryd is”. Very useful indeed in windy the Netherlands.

If you would like to purchase The Secret of Running (or the German version, Das Geheimnis des Laufens), you can do so at the bottom of store.stryd.com.

You can check the impact of all factors on your performance in our book: The Secret of Running

The book explains the impact of all factors determining your performance in running step by step: training, nutrition, body weight, running form, wind, hills, temperature, altitude, running gear, power meters and much more. Written in a crystal-clear and lively style, the book is a wealth of information for every ambitious runner. It details how much power you need to surmount the running resistance the air-resistance and the climbing resistance, It shows how power meters can be used to optimize your training and race result.

Both The Secret of Running and The Secret of Cycling are available in print as well as eBook in multiple languages.