Until now, there has been no way to measuring running power, except through sophisticated force-plate treadmills in a lab.
Running is a simple sport, perhaps to a fault. While you can get plenty of advice and personal coaching to improve your training, fitness and racing strategies, no one really teaches you how to run. But new wearable technology is showing there is a lot we can learn, no matter what level of running experience we have.
In the past decade, there has been lots of discussion (as well as books, articles and videos) about running form and how optimal running mechanics (via drills, core strength, footwear and gait style) can lead to a runner becoming more efficient. While runners have counted footsteps to measure their cadence and monitored their heart rates to determine cardiovascular performance, those aren’t indicators of how much energy they are expending during a run or an indication of how efficient they are.
Last fall and earlier this winter I had the chance to wear-test a soon-to-be-released device called Stryd, a sophisticated-yet-simple tool that could soon become the first true wearable power meter for running. Stryd (Stryd.com) is being developed by a Boulder, Colo., startup spearheaded by Li Shang, Ph.D., an electrical, computer and energy engineering professor at the University of Colorado, and Robert Dick Ph.D., an electrical engineering and computer science professor at the University of Michigan.
What can a power meter tell a runner? Just as in cycling—a sport that has used power as a training and racing metric for years—a runner’s total power output can be quantified with a single number and, when accessible in real time (either audibly through earphones or visually on the screen of a phone or watch) can give a fairly direct indication of how hard that runner is working at that particular moment. That kind of information can be used to monitor progress during a workout or race, improve efficiency immediately or over time or simplify training objectives.
Bringing power into running with this technology serves two purposes, Shang told me. “If you think about the motion of running, it’s really just (the act of) jumping on springs and your legs are the springs,” he said. “So really, the power measurement is helping you understand the motion of your core body and how much power it takes to move your body that way with your legs.”
In developing the algorithm to determine running power, the engineering group took into account air time, ground time, landing angle and a lot of other variables, but those things are hard to see anyway, he says. But by having just one metric that removes variables like body weight or hydration or rest from the discussion, comparisons with other runners can be made. “And the power is not just a measure of how powerful you are, it’s also about how efficient you are,” he said.
Stryd was unveiled to the public on March 3 through a Kickstarter crowd-funding campaign. (A pre-release party was held Feb. 5 at Newton Running headquarters in Boulder, Colo., and the initial consumer products are expected to be available in September.)
How does it work? Using a small sensor pod that clips to the back of a pair of running shorts, a runner using the Stryd system can instantaneously monitor his or her energy output during a run via an Android/iOS smartphone app or sports watch (or after the run via a data upload). The device also tracks numerous other data in real time, including cadence, impact and various other aspects of a runner’s biomechanical form, while speed and distance can be tracked simultaneously on a sports watch or smartphone. (It has a dual-band sensor—ANT+ and Bluetooth Smart—which allows it be to compatible with numerous sports watches and phones.)
Based on my initial wear-tests—running on various mountain trails and indoors on a treadmill—and my brief experiences using a power meter on a bike, it appears like it could be a game-changing breakthrough for running.
For example, while running on mildly rolling trails at a slow to moderate pace, the Stryd device told me my power output varied from about 170 watts to 250 watts. If I consciously improved my form to run more efficiently or found myself running on flat terrain, the power number would be lower. However, if I started running uphill, my power output would increase even though my pace would decrease. Conversely, when I cruised downhill using the “free speed” of gravity, my pace increased but my power decreased.
To test the responsiveness, I ran at what I thought was a tempo effort for about 500 meters up the uncomfortably steep Rattlesnake Gulch Trail in Eldorado Springs State Park south of Boulder and my power number quickly surpassed 300 watts and eventually hovered in the mid-400s.
I also found running on a treadmill at a constant speed for a controlled segment of time produced a fairly uniform power output—likely thanks to a lack of environmental factors such as wind or change in incline. However—and here’s another interesting next-level aspect of monitoring power output during a run—I also gained some initial insights into how my power output and impact with the ground differed when running in various shoes (from minimalist shoes to maximalist shoes) and running barefoot. (Although that data is a bit rudimentary and only a study of one, the power data varied a little and the impact scores fluctuated quite a bit in different types of shoes.)
Put simply, power is energy divided by time or, recalling simple high school physics, power = force x velocity. In practical terms, every time a runner’s foot contacts the ground, his or her speed slows. Then through the push-off stage of a stride, the runner accelerates both vertically and horizontally, and eventually pops off the ground and is momentarily moving in mid-air. Once the opposite foot hits the ground, the deceleration continues until the next push-off. The more deceleration, the more power must be generated to reaccelerate. Applying more power or reducing these decelerations (through greater efficiency) are two ways to run faster over a given period of time.
In other words, power, measured in watts, directly spells out how hard a runner is going stride by stride. Until now, there has been no way to measure running power, except through sophisticated force-plate treadmills in a lab.
“Stryd answers run-by-run, day-by-day questions that runners care about,” says co-founder and coach Gus Pernetz. “Did I pace myself right? Am I overtraining? How is my running form? Am I safe? Until now it has been a lot of guesswork, but Stryd gives runners an objective measurement. And, with better measurement comes better performance. It is truly indispensable.”
Cycling power meters directly measure the force and speed applied to a bike. By measuring the changes in speed to a runner’s body weight, along with incline, the Stryd device is able to calculate the amount of energy used to repeatedly accelerate with each runing stride. Stryd uses motion sensor, an incline sensor and a series of complex algorithms to determine how much power is required to move a runner.
During the initial phase of Stryd’s development, the team compared the device’s accuracy against two established laboratory measures and found a 10 percent range of error. While it has so far been an impressive leap forward toward directly measuring a runner’s effort level, a 10 percent discrepancy is sizable. “The second stage of development will focus on improving the accuracy of Stryd’s power numbers and working with coaches to develop power-based run training programs,” Dick says.
What could all of this mean in the not-so-distance future? Runners could set intensity zones, just like heart rate zones, based on wattage numbers and track this number on a watch to stay at the exact right intensity. Seeing a number that quantifies to an immediate effort value can help runners learn to pace properly during a prescribed workout or during a race. Or, as a runner runs up a hill or over rolling terrain, it is instantly apparent how much energy—and perhaps if it’s too little or too much—is being expended.
However, it must be understood that a runner’s stride is a complex mix of two different energy sources. The first is metabolic: energy produced by the muscles. Fitness limits the quantity. The second is elastic energy. Burning calf and quad muscles give the impression that these muscle groups are doing all the work in a running stride, but in reality elastic connective tissue—including the Achilles tendon, the three arches in the foot and —is stretching and recoiling like a series of springs to re-inject massive amounts of energy into a stride. Because of this dependence on elastic energy return, a perfectly even stride is not necessarily the most efficient way to run. Another variable that could skew the data is an injury history that has led to an imbalance of power in an athlete.
Competitor’s Aaron Hersh contributed to this report.