Pedar Insoles – RPM2 Comparative Data

Differences In the Devices

There are differences between the RPM2 and the Pedar device. The Pedar system is a calibrated insole with an array of 99 pressure sensors distributed over the insole, whereas, RPM2 technology places sensors in four quadrants of the foot bed. In regard to step time, the differences between Pedar treadmill data and the RPM2 algorithm increases to 30-40 milliseconds. This difference, albeit very minute, is introduced by the separate right vs. left foot clocks. It is reasonable that a system like the Pedar treadmill with a single clock would have slightly better accuracy, rather than assume that the right-to-left clock synchronization is perfect. The difference is calculated in milliseconds.

Testing facilities

Following are results of scientific tests when both devices were used simultaneously. Comparative testing was contracted out to Treadmetrix (Calibrated treadmills) in Salt Lake City, Utah. Data analysis was conducted by the Texas Manufacturing Assistance Center (TMAC).

GAIT Comparison  

The data included is the resulting forces from the posterior, middle and anterior thirds of the insoles compared to the same forces from the RPM2 system.  The data displayed in the graphs were obtained during a running exercise at a pace of 6.5 mph.

The following table shows gait values extracted from both RPM2 and the Pedar treadmill system 

Conclusion

For this comparison, the Pedar system was chosen as the comparator since it is a calibrated system. RPM2 and the Pedar system computed similar values and followed the same trends throughout the comparative running events.

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Stride times from the Pedar treadmill system and RPM2 measured within 15 milliseconds of one another, which corresponds to a relative error within 2%. Similarly, swing time comparisons are within 2%. Ground time calculations are within approximately 20 milliseconds; this corresponds to a relative error less than 8% (mostly because ground time is shorter than stride time—the absolute error of 20 milliseconds is still about the same).

Discrepancies of 15-20 milliseconds are rather small in absolute terms, considering that these numbers are drawn from force data which is subject to the usual sensor signal noise and reaction time. Moreover, the data is sampled in 10-millisecond increments (100 Hz), so a single data point "off" already results in this margin of error.

Again, in absolute terms, the RPM2 calculated step times are reasonable, and the percentage error relative to the Pedar treadmill system is less than 10%. The Pedar treadmill system is regarded as a “gold standard” since it is a laboratory calibrated system.

To summarize:

- stride time and swing time: less than 2%

- ground time: less than 8%

- step time: less than 10%

RPM2 is committed to bringing the most accurate device possible to market while still maintaining portability, functional diversity, and affordability. RPM2 offers athletes a viable alternative to currently marketed products that work to enhance athletic performance.