Running with Power

Part 1 of 2 - Introducing Running Power and training with Stryd
Running with Power

Training at different intensity zones to get the best results is a popular training method for runners. Training at different intensities allows specific adaptations to improve our running. Runners have been using heart rate (HR), pace, or perceived effort as a means to determine their intensity. These metrics however are not reliable indicators of training intensity, as external factors are not considered. For example, HR can be affected by a variety of factors including lack of sleep, use of caffeine, stress, and dehydration. Solely depending on HR for training intensity hence can be misleading. Similarly pace can be affected by elevation, wind and many other factors hence is not a good indicator of intensity either.

Running Power: A better way to identify intensity

The cycling world found a better way to train - Power-based training.

Power output in cycling is the force applied by a rider on the pedal and the velocity of the bike. A power meter embedded in the pedal is used to measure the power. Since it measures the actual effort by a rider, it is the best indicator of training intensity. Cyclists use Functional Threshold Power (FTP), which is the highest average power that they can sustain for an hour. FTP is then used to determine training zones.

Running World has been trying to emulate the equivalent of cycling power. Power meters that measure running power are gaining popularity as runners are trying to identify more realistic indicator of running effort. Running power meters measure a variety of factors that influence intensity, and use a mathematical model to calculate the power output of a runner. These factors include running dynamics, elevation, wind, pace, and more. Running power as a means to identify the running intensity is evolving rapidly.

Stryd Power Meter courtesy:

Stryd is one of the popular running power meters which is mounted on shoe to measure power.

Exploring Running with Power

Since April, I have been experimenting running with power. The Stryd power meter has enabled me to explore this (seemingly) un-conventional approach to running. I must say that this is indeed a paradigm shift to the way we approach training and hopefully racing.

After 6 months of power-based training, frankly, there are more questions than answers at this point in time. After years of using metrics such as pace and HR – both intuitive and instructive feedback tools – using power as a feedback mechanism to regulate intensity on runs has involved a steady learning curve for me.

Any new methodology comes with a barrage of new terms and power-based training is no different. The intention of this post on power is not to confuse the reader with all-of that terminology but to introduce the terms as and when they are relevant in this passage.

Critical power is a key metric in the context of running with power. Furthermore, because entire matrix of power zones (equivalent of HR training zones) for running is calculated on this key metric. Stryd defines critical power as follows…

Critical Power (CP) is the threshold at which the dominant type of fatigue your body experiences changes. This number is used to determine your optimal training intensities (Power Zones) which trigger specific fitness gains and guide your race day effort.

Stryd offers two methods to determine the Critical Power for a user: auto-calculated CP, manual calculation of CP. For the sake of this discussion let us keep it simple and go with the auto-calculated CP method. Figure 1 shows my Critical Power as determined by Stryd over a period of 90 days.

Figure 1: Critical Power Reading

An important caveat here, your auto-calculated Critical Power is only as good as the data it receives from your training. The more variety you have in your running, the more accurate your critical power will be.

Why is Critical Power (CP) important?

CP is used to determine your power zones. Power zones are different power ranges that provide guidance when training with power. Power zones give you a general idea of what type of training falls within a power range. In my experience of training with power, you run within a (much-smaller) sub-range of a particular zone rather than dialing into a specific wattage number in that power zone. Fig-2 shows my power zones as calculated by Stryd basis my CP of 270 w.

Figure 2: Power Zones based on CP of 270 w

Let us look at a few examples to understand power zones better.

  • I maintain a power range of about (190 - 195) w for an easy warm-up or recovery run which is approximately mid-range of Power Zone-1.
  • For my slow long run I would maintain a power range of about (220 - 226) w which corresponds to a moderate intensity in Power Zone-2.
  • For a 5km time trial, I would try and stay around my Critical Power i.e. 270 w. I would start at say about 265 w and build my way up to 270 w and eventually peak at about 275 w towards the end of the time trial.

What is Next?

I hope this post gives you a glimpse of what power-based training using a power-meter like Stryd is all about. In my next post, I will write more about the ‘Race Predictor’ feature that Stryd offers, and how I have used it in one of the 10km time trials to race, and ofcourse the results; good and bad.


Kartik Iyer is a conversationalist, running geek, techie, marathoner, miles to go CrossFit junkie and bathroom Carnatic vocalist. He loves striking random conversations with people just about anywhere, music and anyting to do with tech and fitness, in no particular order. He can be reached at @kartikiyer2007 on Insta and on Strava

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