How big is the influence of the temperature?

How big is the influence of the temperature?

We are impressed with Stryd’s Race Calculator. Last week we published Ron’s experience at the Berlin Marathon. As we all know, it was hot in Berlin which caused many runners to run a lesser time, including Kenenisa Bekele (2:06:47 versus 2:01:41 in 2019, so 4% slower).

We noticed in the evaluation of Berlin that Stryd’s Race Power Calculator does not fully reflect the temperature effect for others than elite athletes, nor does it distinguish between light and heavy runners. Earlier, we also saw following the Tokyo Olympics that the Race Power Calculator for shorter distances than the marathon was not quite right either.

For this article, we have therefore listed all the information about the influence of temperature, distance and bodyweight on the performance loss in the heat, both for the readers of our columns and for the programmers of Stryd. We base this on our books (e.g. The Secret of Running) and other literature, as well as our own calculations.

What is the optimum temperature?

All long distance runners have experienced such an ideal race: fast course, nice and flat, windless weather, nice group of runners and an ideal temperature. But what exactly is that, the ideal temperature?

The influence of the temperature on the performance in running is determined in practice by at least 2 factors:

  1. At too low a temperature, we are forced to put on extra clothes to prevent us from suffering from the cold and our body from cooling down too much. Extra clothing leads to extra weight and hinders our freedom of movement.
  2. If the temperature is too high, we have problems getting rid of the heat that we produce ourselves when running and we run the risk of overheating and dehydration due to the sweat loss.

In practice, it appears that the optimal temperature (in windless and dry weather) for the world class runners is somewhere near 5-10°C. You have to keep in mind that they produce much more heat than recreational runners, so that for ordinary runners the optimum will be at 10-15°C. This is cool enough to not get any problems with warming up and warm enough not to need extra clothes.
Please note that wind and rain can lead to hypothermia and performance loss as well!

What effect does a high temperature have on our body?

We must distinguish between the effect of increasing the temperature of our body (hyperthermia) and the effect of dehydration.

When we run we almost always produce more heat than we consume. We use no more than 23-25% of the energy to run. The rest is released as heat. This causes our body temperature to rise and we start sweating, to get rid of the heat.

At a low temperature, a lot of heat can already be dissipated by convection, so we have to sweat less. We then cool down sufficiently by the air that flows past us while running. At a high air temperature, we sweat much more and the danger of dehydration threatens. With a combination of high air temperature and high humidity, we can hardly lose our heat anymore and the danger of heat stroke or collapse emerges.

The increase in body temperature has the important consequence that the blood vessels in our skin dilate, so that more blood flows to the skin and less blood is available for other functions, including our (leg) muscles. So our cardiovascular capacity is actually getting lower; if we run with a
heart rate monitor, we notice this from the ‘cardiac drift’, that is, we run less fast with the same heart rate (HR) or get a higher HR at the same running speed.

The loss of sweat has the effect, among other things, that our blood volume decreases and the blood thickens, which further reduces the capacity of the heart and our performance capacity. Eventually, the pressure in the veins can drop so much that the filling of the ventricle is compromised, forcing the HR to go up even further. If the body temperature rises above 39.5°C, the symptoms of heat stroke may occur (fainting, extreme fatigue, reduced ability to sweat).

Temperature influence at the marathon

Various studies have been reported in the literature in which the statistical relationship between the temperature and the realized times in the marathon has been examined. The best study is that of Helou et al.

They analysed the results of more than 1.7 million participants in the Berlin, Boston, Chicago, London, New York and Paris marathons between 2001 and 2010. They found a statistically significant relationship between the realized times and the temperature, see the figure. They concluded that the performance loss among elite runners (P1) was less than among lesser runners (referred to as Q1, the fastest 25%, the median and Q3, the fastest 50-75%).

The results can be summarized as follows:

  • The optimum temperature is about 5°C (in world class runners 4°C,in ordinary runners 7°C)
  • In the heat (25°C) the speed of elite runners is 6% lower and of ordinary runners 12-18%
  • In women, the optimal temperature is a bit higher (9°C) and the speed loss is somewhat smaller (13% at 27°C). Women therefore suffer less from the heat.

These results are well in line with the previous study by Ely et al that related the performance loss to the wet bulb temperature (which is always somewhat lower than the normal temperature), see the indicative table below:

What is the influence of body weight?

Tim Noakes, the author of ‘The Lore of Running’, summed up the influence of the loss of sweat on performance with the slogan ‘all great marathoners are small’.

In The Secret of Running we have already shown that this is related to the fact that larger and heavier runners produce more heat and therefore have to produce more sweat to dissipate their heat. The most famous example of this is the Atlanta Olympic Marathon in 1996, which was run under tropical conditions at a temperature of 25°C and a relative humidity of 70%.
Many runners suffered from the heat and the race was eventually won by South African lightweight Josiah Thugwane (43 kg), ahead of South Korean lightweight Lee Bon Ju (45 kg). We calculated that these lightweight runners produced ‘only’ 3.3 liters of sweat, against 10 liters for a runner of 90 kg!

If we look at the figure of Henou et al with this knowledge, it is obvious to conclude that the lower performance loss of elite runners compared to ordinary runners will in large part be related to the fact that elite runners are small and light. Roughly speaking, we dare to say that the performance loss will be proportional to the weight of the runner. Where an elite runner of 56 kg has a performance loss of 3%, Ron (80 kg) has to count with a performance loss of 4.3%. In addition to the bodyweight, the talent also plays a role: lesser runners are longer on the road and will therefore suffer relatively even more from the heat.

What is the optimum temperature at other distances?

It goes without saying that the influence of the temperature will be the biggest on the marathon distance. After all, at a shorter distance you will suffer less from warming. Also, it is known that sprinters in particular thrive best at higher temperatures. Their muscles must be sufficiently warmed up to be able to deliver maximum power for a short period of time. What the optimal temperature is at different distances has been investigated in another study (Will le Page, Optimum temperature for elite running performance). The results are given in the table and graph below.

The relationship from this figure makes a lot of sense. At the short distance, your muscles benefit from warm weather and you do not suffer from warming up. On the long distance it is becoming increasingly important that you can lose the heat you produce to the air and therefore a lower temperature is better. If the temperature is too low, you can suffer from hypothermia. This plays a major role, especially in wind and rain.

How big is the influence of the temperature at different distances?

We have not been able to find a good paper with concrete results on the influence of temperature at distances other than the marathon. Nevertheless, after some puzzling, we managed to deduce a relationship ourselves for the loss of time at different distances compared to the loss in the marathon, see the figure below.

We have based this on the study of Helou et al. for the marathon and the following additional considerations:

  1. The influence of the distance will be more than proportional; at the half marathon the effect is clearly less than half of the impact at the marathon.
  2. The influence will be minimal at very short distances; we have assumed that at 3000 meters the loss of time is negligible

With this article we trust to make a good contribution to a correct estimate of the effect of the temperature, weight and distance on the performance loss in the heat and the calculation of this in the Race Power Calculator of Stryd.

Our book ‘The Secret of Running’ is for sale in our webshop. Also available in German as ‘Das Geheimnis des Laufens’, and in Italian as ‘Manuale completo della corsa’


How much faster do you run with the Nike Vaporfly?

How much faster do you run with the Nike Vaporfly?

Nike ZoomX Vaporfly Next% 2 (

We recently received the following interesting question from one of our fans, namely Eddie :

“I am happy to read your articles.
 Read some articles about the Stryd and the Nike Vaporfly.
 The Vaporfly is about 4% more efficient than a regular shoe. I myself use the Asics Nimbus. My Critical Power is 324 Watts. I also have the Vaporfly and I want to use it for the first time for a fast 10 km. If I follow Stryd Race Calculator then I can run this 10 km with a Power of 322 and I’ll finish in 41:30. My question is: what is the impact of Vaporfly on your power? Do you run with the same power faster on the Vaporfly or can you run on a higher power? If it is the last, can you add 4% to your Critical Power?”

We have already informed Eddie that the Critical Power reflects the power of his human engine and therefore does NOT get higher if you wear faster shoes. So he has to run his fast 10K the power of 322 Watts. But because the energy consumption with the Vaporfly is up to 4% lower, at that power of 322 Watts he will run about 3-4% faster than 41:30!

Eddie’s question did encourage us to review the current knowledge and literature about the influence of running shoes on the race times. In this article, we will provide an overview of the energy consumption in running (the so-called ECOR, the Energy Cost of Running) and the factors that influence this, including the recent development of carbon-plate shoes, such as the Nike Vaporfly. A lower ECOR means that you use less energy and can run faster with the same power. At the end of the article, we will answer the question from the title.

How high is the energy consumption in running?

In chapter 12 of our book The Secret of Running, we have included the following table on the specific energy consumption when running on a hard surface (ECOR in kJ/kg/km).

When we consider that various authors have used different methods and the circumstances have also been different, it is remarkable that all values are close to the average. We concluded in The Secret of Running that it is very realistic to use the calculation value of 0,981 kJ/kg/km. This value has now become the universal standard and is also used by Stryd and other authors.

Is the energy consumption the same for everyone?

The specific energy consumption is NOT the same for everyone and under all circumstances. For example, it is well known that some marathon runners, especially the Kenyans and Ethiopians, have a high running efficiency. The running efficiency covers many aspects, the influence of which are not explicitly known. These include:

  1. length (small is better)
  2. physique (long legs, narrow calves, narrow and flexible hips are better)
  3. running style:
    – foot landing (short ground contact, not on heel)
    – arm swing (not in front)
    – stride length and cadence (large strides high frequency)
    – vertical oscillation (effect not uncontroversial)

With the introduction of Stryd, it has become possible to easily measure your individual energy consumption by dividing your specific power (Watt/kg) from a training or race by your speed (in m/s): the result of the division is your ECOR in kJ/kg/km. Please note that you must correct – even in windless weather – for the power needed to overcome the air resistance. This part is virtually negligible at low speeds, but with world class athletes it can be 7% or more.

How do your shoes affect your specific energy consumption?

It has traditionally been known that light shoes have an advantage: in The Secret of Running we have calculated that 100 grams of weight loss provides an advantage of 0.25-1.00 %. Most race shoes are therefore already very light nowadays, in the order of 200 grams.

It was also known from the literature that shoes that use an air-bag and thermoplastic polyurethane foam (such as the Adidas BOOST) can reduce the ECOR by order by 1% because the foam is viscoelastic and returns part of the landing energy.

The function of Carbon shoes such as the Nike Vaporfly has been described by Wouter Hoogkamer et al. (Sports Medicine (2018) 48:1009–1019).

The secret of these shoes is twofold:

  1. they use a carbon plate that functions like a spring
  2. they use multiple layers of viscoelasticpolymers (PEBA) with a thickness of 40 mm.

Hoogkamer measured in the laboratory that the Vaporfly’s spring operation was able to return 7.46 Joule of energy per step compared to 3.38 J for the Nike Zoom Streak and 3.56 J for the Adidas BOOST2. If we divide the difference of 4 J/step for a world class athlete with a stride length of 1.5 m by 666 steps/km and a body weight of 60 kg, we come to a reduction of the ECOR of 0.04 kJ/kg/km. This exactly matches the 4% lower energy consumption that Nike claims!

By the way, the height of 40 mm also provides an advantage because the length of the lower leg increases slightly, as it were, which also has a positive effect on the running efficiency. Several studies have also shown that the stride length with the Vaporfly increases slightly(partly due to the spring action and the height) , which also has a positive effect.

What effect do the new shoes have on the running time?

The new shoes have clearly led to an avalanche of records. The most famous is of course the phenomenal race of Eliud Kipchoge with his 1:59:40 in the INEOS 1:59 Challenge at 12 oktober 2019 (run on Nike Alphafly shoes). The next day Bridget Koskei (also on Nike Alphafly) beat Paula Radcliffe’s 16-year-old world record to 2:14:04. The table below shows that since the introduction of the Carbon shoes almost all world records have been improved on these shoes (Sports Medicine (2021) 51:371–378).

In the tables below we have listed how many % the world records have improved since the introduction of the newly developed shoes for track and road.

The percentage still seems modest (at least compared to the 4% lower energy consumption) but it should be borne in mind that the conditions will not have been ideal everywhere and the level of some old world records was very high (such as those of Kenenisa Bekele and Paula Radcliffe, who were clearly a class apart in their time). It is also illustrative of the latter that Bridget Koskei only improved Paula Radcliffe’s world record by 1%, but her own PR by more than 3%. It should be noted that a 4% lower ECOR value theoretically corresponds to a slightly lower time saving of 3.4% due to the influence of air resistance.

Recent studies on time gains with carbon shoes

In the past year, 4 interesting studies have been published on the time gains from carbon shoes:

  1. The World Athletics Report

They have made an analysis of the best season times of the top 20 and the top 100 runners for the 10 km, half marathon and the entire marathon. They conclude that since the introduction of carbon shoes in 2017, the race times have clearly improved (0.6-1.5% in men and 1.7-2.3% in women).

  1. The Cornell Report

They analyzed the results of 22 North American marathons from 2015 to 2019. The special thing about this study is that they used thousands of web photos and video recordings to determine which shoes the individual participants used. They concluded a benefit from carbon shoes of 1.4-2.8% for men and 0.6-2.2% for women.

  1. The New York Times Report

This is by far the most comprehensive study. They looked at the results of 577,000 marathons and 496,000 half marathons in dozens of countries from April 2014 to December 2019. They investigated the effect of the shoes in 4 ways: with statistical models, by looking at groups of runners who ran the same race, by looking at runners who had changed shoes and by looking at the chance to run a PR in a certain type of shoes. Below are the results of the runners who switched shoes: an impressive advantage of the Vaporfly of even more than 4%!

  1. Hechmann’s research

This is a very special case: a solo study by a passionate Danish researcher that we have written about before. Hechmann is fascinated by our book The Secret of Running and has used himself as a guinea pig. He used ten pairs of different shoes in different weight classes. He used a Stryd and an oxygen uptake device (Cosmed K5). On a treadmill he measured the specific energy consumption according to the Stryd (ECOR in kJ/kg/km) and the specific oxygen consumption (RE in ml O2/kg/km) measured by the Cosmed. The shoes have also been tested on the road. He found on the treadmill that depending on the shoe, the oxygen consumption differed when running with the same wattage. Hechmann found that with the Nike VaporFly (weight 200 grams) he was 8 to 10 seconds faster per kilometer than, for example, with the New Balance More (weight 300 grams). His stride length when using the Vaporfly turned out to be larger than normal.

In the following enumeration and image, Hechmann summarized his research results for the various shoes he tested (size US 91/2).

  • 0 % Saucony Munchen (270 gram) en New Balance 1080 (280 gram)
  • 1% New Balance More (300 gram)
  • 2% New Balance Rebel, (200 gram), New Balance 1400 (200 gram) en Altra Duo (240 gram)
  • 3% Newton distance (240 grams) and Adidas Adizero Takum Zen (180 grams)
  • 4% Nike Vaporfly (200 gram)
  • 6% Nike Vaporfly Next % (200 gram)


Conclusions and follow-up:

  1. The Carbon shoes undeniably have a great positive effect on energy consumption. Nike Vaporfly’s ECOR is 4% lower than the standard value of 0.98 kJ/kg/km.
  2. The time savings of Carbon shoes have now also been proven in various studies (and practice). Due to the influence of air resistance, the time savings are just under 4% (for top runners 3.4%).
  3. The effects are not the same for everyone and depend, among other things, on running style. With a limited flight phase, a responsive shoe is not much use.
  4. The effects depend on the type and manufacture of the shoe. It can be expected that all manufacturers will become/remain active in this technological arms race. This means that the energy consumption and time savings of each shoe type will have to be determined separately (compared to the traditional shoes or compared to the new Vaporfly standard).

Eddie’s question gave us an idea for a practical method to determine the effect of shoes, namely by comparing the running time in a race with the time of the Stryd Race Predictor (which bases its prediction on the power of your human engine during training on training shoes). The lower energy consumption of the race shoes should be reflected in a faster time.

Of course, circumstances also play a role, but with sufficient data, such as in the Stryd Power Center, this can still lead to good results. We will propose to Stryd to develop such an option.

Our book ‘The Secret of Running’ is for sale in our webshop. Also available in German as ‘Das Geheimnis des Laufens’, and in Italian as ‘Manuale completo della corsa’


500 km in 78 hours: is it possible to run the Pieterpad-trail even faster?

500 km in 78 hours: is it possible to run the Pieterpad-trail even faster?

Two weeks ago, the Dutch media reported that Addie van der Vleuten from Best, the Netherlands ran the Pieterpad-trail in 78 hours and 10 minutes. That makes him the fastest ever!
The Pieterpad is the most famous long-distance trail in the Netherlands. The path leads from Pieterburen on the North Groningen Wadden coast to the Sint-Pietersberg in South Limburg. A distance of almost 500 km.

With his performance, Addie raised money for charity. His father died of leukaemia in 2019 and in tribute to him he raised money for KWF Kankerbestrijding (cancer fund). On Friday afternoon 14 May 2021 he left Pieterburen and on Monday evening he arrived at the Sint-Pietersberg in South Limburg. “It was very beautiful and heavy. I ran almost continuously and in the night I had a lot of rain. I’d run with rain pants, raincoat and gloves. That was a pity.” He was aided by a camper van in which he could sleep, shower and change clothes. On some stretches, other ultra-runners also ran along.

Following this impressive performance, we received the following email from another ultra-runner Alex Olieman:

“I have previously enjoyed applying the formulas from “The Secret of Running“. Last week the fastest time of the Pieterpad-trail was greatly improved and I hope that you can help me to go even faster and I have two questions about that:

  1. Is it possible to calculate the maximum achievable speed in relation to rest-running- carbohydrate intake? My plan is to always run 55 min every hour and rest for 5 minutes and sleep from 1:15am-3.45am.
  2. How can Stryd help me to run the Pieterpad-trail as fast as possible?

Alex Olieman is an enthusiastic and talented ultrarunner. Alex ran the 120 km of the unofficial Netherlands Championship ultra-trail edition during the 2019 Indian Summer Trail in 11 hours 17 minutes. The 157 km of the May 1, 2021 UltraPad Netherlands (UPNL) went in 15 hours 24 minutes.

In this article, we answer Alex’s questions.

The energy balance of ultra-running

Earlier we wrote an article about ultra-running following the phenomenal performance of American Jim Walmsley, who ran the 100 km in a time of 6 hours 9 minutes and 25 seconds in Arizona on January 23, 2020. We summarize this article briefly below and subsequently we will discuss the energy balance of the Pieterpad-trail.

We wondered how it is possible to run for 6 hours at a speed of 16 km/h? What happens to the fuel supply (especially the carbohydrates/glycogen) in his muscles? For us ordinary people, the muscles are already empty after about 30 km and we are happy to make it to the end of the marathon.

The secret of the marathon and the ultraloop: the optimal fuel mix

In our books and also in several articles we published, we have previously inferred from biochemistry that the maximum energy production in the muscles of a trained top athlete (fat percentage only a few percent) from the aerobic conversion of glycogen is 7.76 Watts/kg.

The energy production from the aerobic conversion of fatty acids is much lower, namely only 2.36 Watts/kg. This difference is, as we know, the reason for ‘hitting the wall’: when the supply of glycogen has ran out, your muscles have to switch to fatty acids and that provides much less energy/power.

In an article we have already shown that you can easily calculate how fast you can run (v) with a certain power (P): v = P/1.04. For example, we calculate the maximum achievable speed if our muscles were to use glycogen and fatty acids for 100%.

The above clearly shows that the speed drops enormously as the muscles switch from glycogen to fatty acids!

In reality, your muscles never use either 100% glycogen or 100% fatty acids, but a mix of both. If you run slowly, the percentage of fatty acids is high and that of glycogen is low. If you start running faster, your body is forced to use a higher percentage of glycogen, otherwise you will not get the required power.

We have made a further analysis of the existing world records between 5 km and 100 km. For each distance, we know the total power that the world record holders needed to run their times. We then calculated at which fuel mix (percentage of glycogen and percentage of fatty acids) these power/speeds are possible. The result is shown in the table below.

We see a clear and logical relationship: the longer the distance, the lower the percentage of glycogen and the higher the percentage of fatty acids.

We also balanced the consumption of carbohydrates/glycogen during the world records of the marathon and the 100 km. In the table below we first calculate the power that is delivered from glycogen and from it the consumption of carbohydrates in kcal.

During the Vienna Breaking2 marathon Kipchoge consumed about 1892 kcal of glycogen. In order to be able to deliver this, he has of course also taken maximum sports drink along the way. The maximum absorption of carbohydrates through the gastrointestinal tract during the marathon is often set at 40 grams/hour in the literature. During 2 hours this makes a contribution of 2*40*4 (kcal/g) = 320 kcal.

This means that the glycogen supply in Kipchoge’s body at the Vienna starting line for Breaking2 should therefore have been at least 1892-320 = 1572 kcal. This value corresponds well to literature data on glycogen supply in athletes.

For the 100 km we made the same calculations, whereby we have now equated the minimum available stock at the start line with the value of 1572 kcal. Subsequently, we calculated how much carbohydrate intake was needed to be able to supply the consumption. The result is an intake of sports drink/gels of 1059 kcal or 44 grams per hour. This value is therefore slightly higher than the generally applied maximum of 40 grams per hour.

And now the energy balance and the maximum achievable performance on the Pieterpad-trail

To answer Alex’s questions, we first drew up an energy balance for the Pieterpad-trail ,see the table below. With the rule of thumb of an energy consumption of 1 kcal/kg/km, we arrive at a total energy consumption for the Pieterpad of 30,000 kcal (for a trained runner of 60 kg). The vast majority of this energy consumption will have to be supplied by fatty acids because the stock of carbonhydrates (KH) in the muscles and intake during running are limited.

We also set the stock here at 1572 kcal and the maximum intake during the trail at 5000 kcal. The first conclusions are that the muscles will have to use 78% fatty acids and that the stock of fatty acids will decrease by 2.6 kg during the trail.

We then calculated the maximum achievable speed with a fuel mix of 78% fatty acids and 22% carbohydrates. The answer is 0,78*8,17+0,22*26,86 = 12.26 km/h, as shown in the table below.

The speed of 11.09 km/h immediately gives us the opportunity to give Alex’s question about the required Stryd power, because that amounts to 12.26/3,6*1,04 = 3,54 Watt/kg. Alex weighs 67 kg, so he has to try to maintain a power of 237 Watts while running.

To calculate what time is theoretically feasible for the Pieterpad-trail, we need to estimate how much time our runner will rest and sleep on the way. We use the example of Alex, who wants to rest for 5 minutes per hour and sleep 2.5 hours a day. This brings us to a distribution of 18% rest and 82% running. The theoretically best achievable performance on the Pieterpad will then be 500/12.26/0.82 = 49.72 hours.

Alex has shown that in ultra’s over 120 km and 157 km he runs about 10 km/h. If he can do the same with the amount of rest he has in mind on the Pieterpad, Alex will end up with 62.5 hours. That’s a lot faster than Addie van der Vleuten’s 78 hours and 10 minutes.


Theoretically, based on the energy balance, it is therefore possible to run the Pieterpad-trail in rounded 50 hours. If we may extrapolate previous achievements of Alex Olieman to the 500 km of the Pieterpad, Alex’s record attempt does not seem to be without a chance.

Of course this is a theoretical calculation: Hans and Ron do not even think about trying this themselves…. 😀 We are already fully exhausted after the marathon and are certainly not able to run hundreds of kilometers with minimal rest and minimal sleep. We have great respect for ultra-runners who continue days in a row in weather and wind!

Our book ‘The Secret of Running’ is for sale in our webshop. Also available in German as ‘Das Geheimnis des Laufens’, and in Italian as ‘Manuale completo della corsa’


Learned from cyclists

Learned from cyclists

In theory, there is no difference between theory and practice, in practice there is… This tile wisdom once again turned out to be completely correct. What was the case? It turns out at the end of this story.

Last week we discussed the successful 033 Strava Circuit,  a by many appreciated virtual Corona running event. In the meantime, the organization is ready for the fifth and final segment (of 6 km). Participation is open until Sunday 6 June 2021. Even if you haven’t participated before, you’re welcome.

The organization opted for a challenging segment around Soesterberg’s estate De Paltz, domicile of the famous Dutch artist Herman van Veen. Not a meter is flat. It has three climbs and as many long descents.

Tired of cycling

Last week came the good news that Tom Dumoulin is going to the Tokyo Olympics. To ride the time trial there. Tom’s specialty. Tom’s really looking forward to it.

That reminded us of the 2018 Tour de France. Tom won the exciting time trial of the 20th stage. Just how Tom conquered the hills in that stage, exercise scientist Teun van Erp later told tv.

Such a time trial is meticulously prepared. So to speak, meter by meter, Teun recorded the power with which Tom had to cycle to set the fastest possible time. The assignment was clear. Tom had to cycle all the way out to the finish line. Not before, because hitting the wall would cost Tom a lot of time. And no later than the finish, because then he could have been faster.

On his bike computer, Tom could always see his power. Tom won. That is of course his own merit, but without the input of Teun van Erp, it remains to be seen whether he would have succeeded.

The possibilities of a cycling power meter led us to the idea that this would also be great for running when writing the book The Secret of Cycling. A revolution in running. That led to our book The Secret of Running Running with Power has now found its way into the precise Stryd.

From cycling to running

Segment 5 of the 033 Strava Circuit 2.0 offers the ideal opportunity to show how to apply power in running. There are differences with cycling, of course. In a descent and in a bend, a runner can’t freewheel and recover a little. You have to keep powering.

To determine your fastest achievable time on segment 5, we do not need Teun van Erp. That’s what the Stryd running power meter apps are for. Stryd PowerCenter asks for a file with data from the course. If you’ve already run it, you can find it in Garmin Connect, Polar Flow, Stryd Power Center, and all sorts of other platforms like this. In races it can sometimes be found on the website of the race. You can also ask a running friend.

Ron therefore ran the segment twice at an easy pace on Friday. You can then download the .gpx or .fit file. This contains all the information of the course. Height differences in particular are important.

The start and finish of segment 5 are marked with posts in the roadside. Because the classification uses the GPS registration in Strava, it is wise to start well in front of the pole and finish a lot behind the second pole. GPS is not always accurate.

PowerCenter itself extracts the distance from the read-in file (see image above). The average elevation of the course also emerges automatically. You have to indicate at what elevation you have trained. In the Netherlands, of course, this is pretty much the same level. But if you train on the plateau in Ethiopia or Kenya, you have an advantage at sealevel. And the other way around a disadvantage. PowerCenter takes this into account. Similarly, the temperature is important. The humidity only at high temperatures (in case evaporation of your sweat causes less cooling of your body).

Based on your personal critical power and power duration curve, you will automatically get the race power to set the fastest possible time for you. Then you are empty right on the finish line with a satisfied feeling.

For Ron, the advice is to run flat at 284 Watts. That means you run uphill slower than average and downhill faster. That takes getting used to. Many of us tend to take a hill firmly. With a red head breathing down the top and then catch your breath again in the descent. Then you don’t run your fastest time.

In the image below you can see in grey the elevation of segment 5. If Ron averages 284 Watts on this segment, it yields a calculated race time of 30:01.
The blue line shows the calculated speed on the slopes if he sticks to that 284 Watt neatly. Slower uphill, downhill faster.

This is the theory.

Now to practice

When segment 5 was explored on Friday, it was dry. In between the showers, even a moment of sunshine occurred. On Saturday, the attempt had to take place. It seemed to rain a little less. That’s why Ron got off to a fast start after a very short warm-up.

A rookie mistake. In the first descent, the 284 Watt proved just too high for the still stiff legs. Then the weather forecast appeared to have overlooked a downpour….

Race time 30:33, with an average wattage of 280 Watts. So not quite the best result.

Unfortunately, time alone does not count for the classification of 033 Strava Circuit 2.0. The dark clouds, the rain and the wet foliage appear to have caused such a deviation from the GPS that Strava did not recognize the segment. While Ron really ran from pole to pole ….

There’s nothing left but to try again. Under better conditions. And with a few watts more.

Finally, a few comments

There is no need to look at your watch all the time to check if you are running with the intended power. You check that every now and then. With changes in slope, you can check if you are still OK.

The last 20-30 meters before the top of the 1st (and 3rd) climb is extra steep. Ron ran there at 350 Watts. No problem. You don’t have to slow down and reduce power for such a short stretch. That would be a sub-optimization which is not necessary.

On a course like this, you notice that it’s no use to run at pace or heart rate. Power clearly has added value.

Our book ‘The Secret of Running’ is for sale in our webshop. Also available in German as ‘Das Geheimnis des Laufens’, and in Italian as ‘Manuale completo della corsa’


Convert to a training plan on power

Convert to a training plan on power

Last week we got into a conversation with Willem de Ruijter. Willem has his own running school and trains a performance group of athletics club BAV in Baarn. From our own experience we know that Willem is the address for running style training. He trains athletes of all levels. Athletes who train purposefully to improve their performance in races, but also beginners who want to work on their fitness. Willem can read and write with training plans based on heart rate and he is like many others interested in running on power (he also has a Stryd himself). Among his athletes, running with power meters is increasingly in demand.

Willem himself is a talented runner. In his age group he regularly makes it to the podium at the Dutch championships. Internationally we see him participate in just about all tournaments for masters, indoor and outdoor. He always is present at the cross-country races.

Tailor-made plans

Running plans can be found on the internet. In our article Vary in your training last week we gave a number of websites. These kinds of plans are actually a kind of starting point. The same applies to the basic plans that performance trainers like Willem use.

Obviously, it starts with the athlete’s goals. Is it medium or long-distance? Or is it an athlete who runs the year around a variety of races and also goes for a marathon? The number of days and the amount of time someone has available is a second important question. Can someone train every day or is it preventively necessary to schedule recovery? Does the athlete run a lot of races so that training targets have to be target on race paces?

And of course, training is not just about following a plan. The evaluation and adjustments are at least as important if you want to work towards great performance. Stryd offers a digital trainer on your shoe with the footpod. That’s nice. Especially if this suits you.

Of course, it never replaces the experience and personal approach that the trainer can give at an athletics club or running group.

The training doctrine based on power is no different at its core than usual. Of course, the human body is the same. Heart, lung and, muscles and your metabolism are still the same. If you want to start with plan on power as a trainer, you can therefore convert your own schedules to power as a start and gain experience and fine-tune from there.


We give an example of how to easily calculate the wattage with which the athlete has to run according to plan: Suppose the athlete has to run a block at 10 K race pace. He or she weighs 70 kg and runs the 10 K in 50:00. The plan then actually requires a pace of 5:00/km. Over 1000 meters (1 km) this is 300 seconds (5:00), so 1000/300 = 3.33 meters/second.

The wattage (power) with which you have to run that block is then 3.33 m/s*1.04*70 kg = 242 Watts.

Another work-out can be to run a 400 meters in 28 seconds per 100 meters.

You then run 100/28 = 3.57 m/s. The corresponding wattage can be calculated as 3.57 m/s*1.04*70 kg = 260 Watts.

In this way, the wattage can be calculated in all situations. Regardless of whether it is an endurance run, blocks, or interval over a certain distance or duration.

If you want to know where that factor 1.04 comes from, we refer you to an earlier article. At ProRun you can also find our calculator that takes this calculation off your hands.

Heart rate

For the conversion of a schedule based on heart rate, we have placed the table from the article Vary in your training again. For the conversion of the training schedule to power, look in the table at the training goal and the training form you want to advise the athlete and choose the corresponding percentage of the FTP.

For this it is necessary to know the FTP of the athlete. This Functional Threshold Power is the power that he or she can sustain for an hour. You can determine this based on race experience, you can read it in the running power curve  or determine it with a specific test .

Athletes who want to train with power in most cases have a Stryd. Stryd generates a wattage called critical power (CP). Simply put this is the wattage with which the athlete runs a 10 K. For performance-oriented runners, that’s (much) shorter than an hour. Consequently, the CP is a few percent (maximum 5%) higher than the FTP.

5%? That 5% goes for an athlete who runs the 10 K in 30 minutes. This gives you a general rule of thumb as a tool. Doubling or halving the distance or time makes a difference of 5% in wattage. During a 5 K the athlete can run with 5% more power than during the 10 K. The half marathon runs the athlete with 5% lower power than a 10 K for the best performance.

Below the table, using a schedule we borrowed from our athletics club Altis, we worked out a two-week sample schedule.

The diagram below is for an athlete with a CP(critical power) of 302 Watts. He got this value from his Stryd. Stryd automatically adjusts the CP. If the athlete improves through training, the value increases and he benefits from training at higher power. If the CP decreases, he would do well to slow down a bit and build up from there.

In the second week of the schedule, a race is scheduled on Tuesday. If he chooses the 10 km, he focuses on the wattage of his CP (300 Watts). For the faster 5 km he should race at 315 watts.

Depending on the training form, the other days the wattage ranges are given with which you have to run. The ranges are related to the FTP from the table above.

If instead of the FTP the CP has been used to draw up the schedule, the athlete would do well to stay slightly below the maximum wattage. After all, the CP is in most cases slightly higher than the FTP.

Depending on what you want to achieve, schedules differ. In our free e-book The easiest way to a PR: Running with Power (in Dutch, Enlish edition is in progress), this is explained, even if you train not on power but on heart rate.

Our book ‘The Secret of Running’ is for sale in our webshop. Also available in German as ‘Das Geheimnis des Laufens’, and in Italian as ‘Manuale completo della corsa’