What is running power?

Power is the mechanical measure of running effort and intensity. Power indicates how much energy you are expending during the run and how fast you are expending it. Power is determined by calculating the amount of work done per unit of time as described by the formula:

Power = Work / Time

To better understand what power is we first need to get a better understanding of work. Work is equal to the force applied multiplied by the distance applied:

Work = Force x Distance

We can now substitute Force x Distance for work, resulting in the new expression of power as:

Power = Force x Distance / Time

Distance divided by time is also known as velocity, which is more commonly referred to as speed. If we substitute velocity into this equation we now have:

Power = Force x Velocity

This equation for power is where we would typically end while explaining how power is measured on a bike. On a bike, power is basically determined by multiplying the force applied to the pedals by the rate at which the pedals turn (cadence). However, running power meters do things slightly differently.

Stryd breaks down the above equation further. Force is equal to the mass of an object multiplied by its acceleration:

Power = Mass x Acceleration x Velocity


The mass of the object (you) is given and Stryd takes extremely accurate measures of your acceleration and velocity to calculate power, measured in watts. Running power considers speed , form, and elevation. Runners need quality training and guidance to succeed in their next race. Many runners struggle to find a repeatable and reliable way to attain high quality training and racing. Everyday there are questions that need correct answers: When should I run next? How hard should I run? Stryd answers these questions with a metric new to the running world: power.

This white paper evaluates the accuracy of the Stryd’s measurement of running power, ground time, and vertical oscillation, by comparing it with a lab grade force plate-based treadmill and a metabolic measurement system.

Pacing Workouts/Races

Steady-state workouts and races require the energy to be expended in a well-calculated manner. This is hard even for the most seasoned athletes. Most athletes go out much too fast at the start and pay the price in the second half of the race by having to significantly slow down. With a power meter, however, runners can pace themselves in a much more precise manner than with GPS readings or a HR monitor. GPS accuracy is dependent on weather, course conditions, satellite reception, etc. Heart rate is affected by temperature, caffeine, how much sleep you got and a whole host of other factors, whereas power is much more precise, these factors do not impact the calculated power. But proper pacing goes well beyond the common problem of going out too quickly at the start. It also eliminates the guesswork of pacing on hills, descents, and HR fluctuations. Pacing with power eliminates all of these and thus gives confidence to the runner

Why not heart rate, speed, or feel?

Power and speed are measures of output, they tell us what is being accomplished during a run. Heart rate and feel are input, they tell us what the effort is to create the output. Performance in the race is directly related to your output, not input. The input simply reflects what the runner is experiencing. The output decides who is going to come across the finish line first. Compared to speed, power is not affected by terrain change and actually capture the performance impact caused by running efficiency. Unlike speed, power will show the real-time energy costs of running up and down hills allowing the runner to accurately know their energy expenditure over the course of a run. Here in lies the greatest benefit of pacing with power, a single numerical target to follow the entire race. If you want to see the whole picture of the training, heart rate, speed and feel are still important metrics, it’s just that looking at the run through the lens of power makes better sense of all that you are seeing and experiencing from the other three, it makes them more relevant, clearer and more meaningful.

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Case Study of using Stryd in Training and Racing:

Coach JJ has been coaching Wim with Stryd Run Power for a month now and had tested and set his Critical Power using INSCYD software and modelled his pacing and nutrition strategy, the power pacing was so good that he improved his time by 25 minutes from 2.11.35 (2017) to 1.46.13 (2018) that’s an increase in Pace from 6.21 to 5.07.
Wim was 2nd in his age group by only 42 seconds and would have won but he lost 2 minutes in T1, due to a helmet strap issue.
Running with power and using INSCYDS takes all the guesswork out of how fast to run and how to plan nutrition. JJ is the only coach in Thailand to have the technology and knowledge to Test Critical Power accurately run power and set pacing and nutrition strategy, which also helped Wim set a new 90 minute Cycling Power PR but still leaving him fresh for the run.

Wim wrote in his feedback:-
“looking at peak heart rate post race, this is my biggest effort every in a run. I felt incredibly strong, I don’t really understand why; I was still fresh after the bike ride, that also helped. I started to run and went immediately to 320 watt, I slowed down to 300 W which felt still too easy. After 300 m, i had to run up the infamous steep hill for the first time. I tried to maintain power at 300 W and I went smoothly over the hill. I felt so good on the flatter parts and even on the other hills that aren’t so steep. Still when I u-turned I could see k. Amnad running smoothly. I tried to go over 300 W but then i started to breath heavy immediately. I decided to stick to my tempo. After 1.5 lap, k. Amnad passed me finally. I tried to keep up with this tempo but that again meant running at 320 W and heavy breathing. I tried to stay as close as possible but he would not slow down. I kept on pushing, maybe not killing me, but really pushing hard but I could not catch him. I was very satisfied with my second place especially my run” – Wim Martens

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