Power meters for running may not give the same absolute info as cycling power meters, but that’s not necessarily a bad thing.
Running power meters rely on a combination of accelerometer motion sensors—vector detectors—and complex software algorithms to convert the measured data to assign a power value. It’s a lot different than how most bike power meters work, which gauge real measured energy output from the force applied to the pedal, calculating an objective wattage figure based on your power, multiplied by the stroke rate.
Comparatively, running power meters aren’t as accurate of a measure. Consider them more an indicator of relative effort. As Martyn Shorten, founder of the Portland-based sports product biomechanics lab, BioMechanica, puts it: “These devices are not measuring ‘power’ but trying to measure something that correlates with ‘effort.’”
And that measurement itself can be a useful training tool. Just like in cycling, a runner training with “power” can use their relative numbers to understand pacing on hills and pacing during races, regardless of conditions or heart rate (which can be affected by outside influences like sleep, temperature, and even caffeine intake). The goal: run at the lowest wattage for the fastest pace—a sign of efficiency.
The two major brands of running power meters currently available are Stryd—which measures all three power planes—and RPM2, which measures vertical and horizontal planes but just estimates the lateral, a less-important factor in the calculation of running power. Stryd uses a foot pod and RPM2 uses an insole.
Dr. Josh Emdur, Medical Director of SteadyMD Running, an online primary care practice for runners, is a Stryd devotee who credits it with a successful Boston qualifier at the 2016 Marine Corps Marathon. Emdur’s coach reviewed his power data from a training cycle and pegged 250 watts as the figure to stick to during the race. This “power ceiling” is the type of measurement that is extremely useful to long-course triathletes trying to pace evenly on hilly courses or after a tough bike leg.
“Being able to see the power in real time on my watch really helped with my pacing,” Emdur says. As for heart rate versus power, Emdur notes that an increase in heart rate “is almost impossible to avoid if you are really pushing your limits towards the end of a marathon.” Going into his event, Emdur’s training cycle lacked the volume he would have liked, but his power data provided him with hard-numbered confidence. “I could see that on my long runs my power was consistent without changes in my form,” he says. “From this information, I knew I was ready to race.”