Power Meter questions

Power Meter questions

Here are some questions runners have asked about power meters.

Running power meters don’t measure the force being applied – how can they calculate power?

Cycling power meters can use pressure and strain gauges to accurately measure the force being applied, and calculate the effort (power) from that. Running power meters don’t measure the force being applied – how can they calculate the effort (power)?

Running power meters use accelerometers and other sensors to measure foot (or wrist, or torso) movements, plus a complex algorithm to convert the measurements into power.

But the use of an algorithm doesn’t mean the numbers are unusable – as long as the power meter produces repeatable, valid results:

✅ Repeatable? The same effort under the same conditions gives the same result.

✅ Valid? The numbers are highly correlated to an existing ‘gold standard’.

The Stryd footpod has been validated more than 10 times and confirmed to produce repeatable results correlated to oxygen consumption.

Wrist-based power (from Garmin, Apple and Coros) has been tested by my N=1 study – the numbers were repeatable and were correlated to Stryd footpod numbers.

Garmin numbers are nothing like Stryd numbers – how were they correlated?

Garmin power numbers are generally 30-35% higher than Stryd numbers. With large differences in the power numbers, how could the numbers from the N=1 study correlate Garmin power numbers to Stryd footpod numbers?

The study didn’t use a direct numbers-based correlation.

Instead I wore multiple watches on runs at a variety of paces and in a variety of conditions. The watches each recorded the runs.

Critically, I included some maximum effort runs, and from those was able to calculate Threshold Power for each watch configuration. I was able to use the Threshold Power as a basis for comparison – for example, if I ran an easy run at 75-80% of Threshold Power (as measured by my Stryd footpod), did the other watches also report 75-80% of their Threshold Power?

Using this relative (to Threshold) comparison I was able to confirm a correlation.

Sounds like there’s no standard for running power?

Running power numbers differ between manufacturers. Why?

Garmin and Polar use algorithms that estimate external mechanical power. Stryd, Apple, Coros and other brands use algorithms that align to internal metabolic cost.

And each manufacturer has its own proprietary algorithm, which produces differences between the power meters, even when the algorithms are based on the same approach.

All of which means two things:

1. You should not directly compare power numbers from different power meters; and
2. You should not mix power numbers from different power meters – choose one power meter and use that power meter only.

Which is the best Power Meter?

It depends on your budget, and your appetite for handling complexity.

Budget-wise, it’s always going to cost less buying one device compared to two – a watch with wrist-based power will cost less than a watch and a Stryd footpod. If you only have a small budget and your running watch is relatively new, you may choose wrist-based power.

But that’s only part of the story.

The Stryd footpod comes with the Stryd ecosystem, which is built to handle power, from the on-watch experience through the calculation and use of power metrics. It includes training plans, access to coaches and a library of power-based workouts (some features require a subscription).

If you use wrist-based power instead, you’ll need to put together your own ecosystem – and that can get a little complex. Fortunately, these kinds of decisions are covered in detail in ‘Running with Power – Getting Started‘.

Bottom line, the ‘best’ Power Meter is always going to depend on your circumstances – your budget, and your appetite for handling complexity.