Pace & Distance Accuracy

The importance of accurate distance and pace metrics

At some point in almost every runner's journey, they decide to upgrade to a GPS watch. This purchase comes with an expectation that this new ‘gadget’ will provide accurate data about running performance. Having dropped the cash, understandably, runners place a great deal of faith in the values being shown during the run and the accuracy of the reported data. After all, the whole point of buying a GPS watch is to get a better measure of running performance.

Let us start by looking at the two sides of the argument: accuracy of the wearable device versus the magnitude of running improvement. Runners who own a GPS watch typically care about three notable metrics: distance covered, running pace, and split time. In most situations, they can be confident in the timing information provided by a device. However, pace/speed metrics rely on devices measuring distance accurately and then using a formula [speed = distance ÷ time, or pace = time ÷ distance) to determine these values. And this is where the accuracy of the data begins to break down.

It’s important to remember that runners may only be making modest improvements in performance. Runners want these improvements to be tracked accurately allowing trends in running performance to be identified. Therein lies the problem. What if the error in their device is as big (or bigger) as the performance changes they are making?

What level of accuracy do runners actually need?

Sport scientists have concluded that a meaningful change in endurance running performance for everyday runners is around 1.5% and for elite athletes it could be at as little as 0.5%. On the other side of the equation, the typical error for even a high-end GPS watch is about 2-3% in distance terms. Equating to around 20-30 metres of error in every km.

Where this starts to get interesting is when we look at what this actually means for the runner. An athlete who is running at 04:00 min/km will be getting told by their watch that they are running at 04:07 min/km (assuming a distance underestimate). Any seasoned runner will know (and feel) the difference between 04:00 and 04:07 min/km pace. However, by relying on the watch as the benchmark for pace, rather than perceived effort, they increase the chance of working too hard too early and blowing up before the end of the run.

For longer-term analysis, if runners are viewing run data that has 3% or more of (possibly random) error, then it is going to be difficult for them to use their data to see trends in their performance. In short, runners need better, more accurate, performance data from their wearable devices.

The limitations of current approaches

Most current running watches rely on GNSS (or GPS) satellite technology to repeatedly locate where a runner is on the earth’s surface at any instant of time and then use the distance between locations and the regular time intervals to reconstruct the runner’s speed/pace.

Even in ideal conditions, GNSS technology has limits to its accuracy which will negatively affect the validity of the data. These inaccuracies are compounded further by factors which disrupt the satellite signals. These include the number and location of available satellites, weather or atmospheric effects and interference from tall buildings or tree cover. If you own a GPS watch you will have, undoubtedly, experienced the impact of the built environment on your run - it’ll be that race or training run with spikes in distance and pace that differ drastically to the actual effort.

Adding to the potential limitations of GNSS/GPS technology in challenging outdoor environments, it is also essentially impossible to use GNSS tracking to monitor running performance indoors, either at indoor tracks or during treadmill sessions.

The application of inertial sensors

A small number of current devices have avoided GPS technology for reconstructing distance and pace measures in favour of employing an inertial navigation (INS) approach. These devices benefit from accuracy improvements under most conditions but suffer if they fall back on phone-based GPS traces to show route coverage. Another benefit of an inertial sensors approach is that, in theory, there is nothing to prevent the INS devices being employed for indoor and treadmill running.

The NURVV solution

The best current solution for providing runners with the accurate performance data they need is a careful fusion of top-line GPS data with an advanced inertial navigation system using complimentary onboard sensors.

The technical specification of the sensors collecting the raw data must be cutting-edge – running is a very dynamic activity and the GPS data needs to be collected at a high enough sampling rate to follow the quick changes of direction a runner makes. Also, the inertial sensors need to have high enough sampling rates and dynamic ranges to robustly capture the rapidly changing waveforms and magnitude of impacts that occur during running steps.

During its development, NURVV Run has considered all these factors and arrived at a technical solution which provides market-leading accuracy for running performance data. This has been confirmed by internal and external testing.

NURVV Run represents the best choice for the runner who wants to be super-confident in the numbers their device is giving back to them, and who is seeking to monitor those coveted marginal gains that accumulate and lead to meaningful improvements in performance.