Running on Power
While new to running, power meters are already mainstream in cycling. Power is more reliable than time, speed, cadence or heart rate alone for evaluating performance. As such, many cyclists are constantly aware of their power output when racing and use power zones as guides for more effective training.
There are many types of cycling power meters, but each one uses a strain gauge to measure the force your body exerts on a component of the bike. That force is then multiplied by the angular velocity of the component to calculate power output.
In running, it’s a bit more complicated. There’s an axis of motion to appreciate at every joint, as well as effort during both stance and swing phases of gait to consider. Stryd is trying to appreciate this complexity of movement and its metabolic requirements using a single-sided foot pod.
Careful to protect their proprietary secrets, Stryd isn’t sharing their equations, nor their specific understanding of running mechanics. There’s no gold standard against which to compare their product, so it’s difficult to validate their technology. But, they do welcome inquiries through their website’s live chat feature.
A year after its debut and already in its second iteration, the Summit is a sleek foot pod that clips onto your laces. It comes with a wireless charger, is compatible with some of the most popular Garmin and Suunto gps watches and has Android and iOS compatible apps that are polished and easy to use. In addition to power, the Summit measures pace, elevation, distance, cadence, ground time, vertical oscillation, form power and leg spring stiffness. Stryd has priced the Summit at us$ 199, which is reasonably affordable compared to cycling power meters, which start at about four times that price.
On my first run with the power meter, there were no surprises. The power display responded accordingly when I ran faster, and it spiked when I ran up stairs. The distance and elevation changes recorded on the app were accurate, as well.
Outdoors, changes in speed are measured by the gps in your phone or watch, and the elevation of the terrain is measured by the foot pod’s barometer.
Indoors, the treadmill mode is essential and requires that you input your speed and the treadmill incline, and update them throughout the run. This is a bit of a hassle, but Stryd says they know how they’ll measure incline automatically in the future.
The user’s stated weight is another major factor in Stryd’s equation, ref lecting the biggest difference between running and cycling power meters, the latter being blind to the rider’s size.
It might seem strange to calculate power using a formula that hasn’t been vetted and requires users to input treadmill inclines and speeds as well as daily weight f luctuations to get an accurate reading. But, power aside, the accelerometers and gyroscopes in the pod are measuring other metrics that may be useful as well.
Stryd claims that you can improve your running efficiency if you find the technique that uses the least power at a given speed. To test this assertion, I experimented with different techniques while maintaining a constant treadmill speed.
I found no difference in power output between “gazelle” and “shuff ling” technique. However, “form power,” which represents the effort required to lift your centre of mass in preparation to move forward, did increase slightly with gazelle technique and decreased slightly with shuff ling. Leg spring stiffness is a measure of efficiency that also increased with the gazelle technique.
When I mimicked a bouncing technique, my vertical oscillation and form power increased, as expected, indicating decreased efficiency.
According to the Stryd team, the greatest efficiency is achieved by striking a balance between form power and leg spring stiffness. I struck a balance between the two by using the gazelle technique while increasing my cadence from 165 to 180 steps per minute. Leg spring stiffness remained high, while form power decreased by a whopping 9%.
In November, triathlete Lionel Sanders was wearing the Stryd Summit for the first time when he set the Ironman world record in Arizona. Two weeks later, at the Personal Best triathlon clinic at McMaster University, Sanders reported that he would be using the power meter ongoing as a training tool. He noted his leg spring stiffness declined gradually over the course of his run, indicating the effect of fatigue, and wondered if he could improve it by focusing on maintaining his form.
As athletes and coaches grapple with questions like these, trying to determine what the data means and how to use it, one thing is clear: they’re excited about the technology. While the device can’t fully assess your technique, it can help, and the metrics do give context to an effort. I suspect running power meters are here to stay. Time will tell whether it’s a fad or an important training tool. Justin Vanderleest is an FCAMPT physical therapist based in Toronto. Visit justinvanderleest.com and follow him on Twitter @JDvanderLeest