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What about the Polar inertial sensor technology that Polar uses?
The inertial technology that Polar uses is very advanced, inertial technology is used in
aerospace positioning and guidance systems, industrial robotics and in advanced
automotive applications such as active suspensions and emergency airbag deployment
to name a few.
The inertial sensors measure the acceleration of the S1 foot pod more than 1000 times
per second and use this data with advanced algorithms to calculate foot angles and gait
velocity the Polar S1 running speed and distance sensor is NOT A PEDOMETER.
Instead, it is very advanced running speed sensor.
How it works
The foundation of the inertial technology is that the foot continually accelerates and decelerates with each stride. With the pod attached to the foot the major phases of gait can be extracted from the sensor signals using advanced DSP (digital signal processing) techniques (as shown in Figure 1). The footpod measures the accelerations throughout each stride, computes foot angles, and then determines the resultant acceleration in the direction of travel. These data can then be integrated for each and every stride to arrive at the information it provides in real time to the user.
What makes inertial technology particularly unique is its user independence, accuracy and ease of use. Right out of the box, the accuracy of the distance computation using the inertial algorithm during running is typically 97%.
As mentioned, one of the inherent advantages of inertial technology is it actually tracks and recreates the motion of the foot through its stride. By recreating each and every stride, it identifies the length of each stride to determine the distance a runner travels in the forward direction.
Inertial technology measures accelerations in the forward and vertical directions. The
accuracy increases to 99% with calibration. In relative terms, this accuracy is as good or
better than the accuracy provided by GPS.
The following is a diagram developed from the data collected with the inertial technology. It shows the path of the foot measured during a walk, jog, run and sprint. Notice the difference in stride length for the four different types of gait.
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