ULP Wireless Update

Runners adopt power monitoring

Runners adopt power monitoring

Stryd power meter takes advantage of a highly-integrated wireless SoC to reduce the device’s form factor

Advanced sensors are improving runners’ workouts

Running footpods were among the earliest wearables to be developed, but other than becoming smaller, lighter, and more accurate, not much about them changed in the decade following their adoption. Development focus shifted to other sports, because knowing speed, distance, and heart rate was perceived to be all that was needed by runners, many of whom loved the simplicity of running as a form of active meditation.


But as the world of wearables grew, and the landscape changed around runners to include ways to log, share, and analyze their current performance, the idea of running faster, stronger, and better took hold. Training plans based on pace and heart rate zones are standard in running today, but they are steadily being augmented and/or replaced by a host of new metrics that have become available in recent years. Running power is chief among them.


According to Olympic running and triathlon coach, Bobby McGee: “The holy grail in running has been to discover such a factor - measuring power in running as a unit.” Knowing running power enables athletes to compare their effort across runs more effectively. For example, running uphill or into a wind requires more power to maintain the same pace. Similarly, running on softer surfaces will burn more power than running on asphalt. Monitoring heart rate gives an indication of how hard an athlete is working and will therefore remain a key figure for serious athletes to monitor. However, the power measured by running power meters does not include any lag, and makes it easier to see why the heart rate has started to rise. Being instantaneously responsive, power monitoring also enables athletes to see the effect of changes to their running form in real time, thus helping them pursue greater efficiency.


Early prototypes and Kickstarter projects have produced advanced running power sensors that function, although a fully interoperable end-to-end solution is lacking. Instead of using a regular sportswatch or smartphone app to connect with the sensor, the download of a proprietary app is needed, as is the tedium of a multistep process to add running power data alongside other metrics in popular apps such as TrainingPeaks or Garmin Connect. Alternatively, for running power meters, the user can set their watch into cycling mode and upload data normally, and then edit later to show up as a running session. Neither of these approaches make for a great user experience, or encourage adoption of the new metric.


Until now. As Dirk Friel, co-founder of TrainingPeaks puts it: “It looks like the future has arrived, a power meter for runners that will advance training methods by decades”.


Towards interoperability

That future comes in the form of an end-to-end solution that works for runners. Last year, Athlete Architect, a Boulder, CO-based technology-centered sports and fitness company, launched Stryd, a wearable device for measuring running power. The device offered both ANT+ and Bluetooth low energy wireless connectivity, using Nordic Semiconductor’s nRF51422 multiprotocol System-on-Chip (SoC). This August, the company will be relaunching its running power meter.

Stryd has been completely redesigned, and will now be worn on the runner’s shoe, rather than clipped to the back of their shorts as the earliest versions were. More importantly, from a use case perspective, it is being launched complete with a Connect IQ app, which once downloaded onto a compatible Garmin watch, will mean users can keep the watch in run mode and see their real time power number on the screen as they work out. Stryd promises a solution that fits with a runner’s existing products and habits.


Stryd demonstrates that one option developers have is to wirelessly transmit data from their running power monitors. While no ANT+ or Bluetooth low energy profile specifically designed to transmit running power data has been published, a solution based on the ANT+ Bike Power Device Profile or the Bluetooth low energy Cycling Power Profile works well and offers the best opportunity for users to see their data on existing displays.


It’s also possible to interleave manufacturer specific data pages to transmit advanced metrics such as pronation angle and leg stiffness. However, until these additional metrics are more widely adopted and standardized, then proprietary apps will be needed to display the data.


If a sport indicator was added into the ANT+ or Bluetooth low energy cycling power profiles, manufacturers could enable sensors to indicate to displays for which sport they are being used. This would be particularly useful for multisport power meters, such as RPM2’s product, that can measure both running and cycling power. (RPM2’s device is built into a pair of insoles that measure force and transmits total power, left-right power, and bilateral equivalency among other metrics.)


Alternatively, if the device is intended to operate in a closed ecosystem of devices, then manufacturers are free to define their own transmission protocol and send the data on a private ANT network. DorsaVi is an example of such an ANT- based multisensor system and is used to analyze sophisticated biomechanical parameters during running. DorsaVi requires training to use and is employed by professional team trainers and physios, as well as specialized running coaches.


Matching market needs

Nordic Semiconductors’ nRF51 and nRF52 Series SoCs allow manufacturers to choose configurable ANT and Bluetooth low energy SoftDevices (RF protocol software or ‘stacks’) to keep their protocol options open, enabling them to adapt to new developments in ANT+ and Bluetooth low energy profiles, and corresponding development by sportswatch, smartphone, and bike computer manufacturers. In a new market such as running power, having the flexibility to adapt the wireless strategy without incurring any costly hardware redesign and minimizing firmware changes is a significant advantage.

Having this flexibility in a compact SoC format is even better. The algorithms required to compute advanced running metrics such as power are complex and need substantial processing power, which demands a rechargeable battery. A compact SoC integrating radio, processor, Flash and RAM leaves space for a lithium-ion (Li-ion) cell without adding bulk or weight.


While running power meters are a new product category and it is unknown how popular they will prove to be, the potential market is substantial. In the U.K., running is ranked as the second largest sport by participation numbers (following swimming, and followed by cycling) with an estimated ten million participants (out of a 62 million population) with around five million participants in competitive running events. In the US (population 326 million), 17 million runners participated in competitive events. And in China (population 1.5 billion), where running is a newer fascination, 2 million participants competed in events in 2014, a number which has been rising significantly over the past decades.