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I was wondering how I would justify a sampling rate of 125 Hz for accelerometer and gyroscope data from wearable sensors. This is a rate used in a lot of biomechanics literature, but I can't seem to find a justification.

I have been looking up the Nyquist rate, but I'm not sure how to find the bandwidth of the IMU signal.

Any help in this justification would be great

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  • $\begingroup$ It's probably "high enough" and "commonly used". Don't expect a justification. $\endgroup$
    – Marcus Müller
    Commented Sep 2, 2019 at 15:19
  • $\begingroup$ It depends on your mode of operation. If it is bluetooth, 125 Hz is a reasonable sampling rate. However, if it is wired, it can go all the way up to 1000 Hz. $\endgroup$
    – Maxtron
    Commented Sep 2, 2019 at 16:08
  • $\begingroup$ It is a wireless bluetooth sensor, I am just wondering because I might have to justify it for an exam $\endgroup$
    – Eric
    Commented Sep 2, 2019 at 16:20
  • $\begingroup$ @Eric It should be easy to compute right. You have six channels (three-axis accelerometer and three-axis gyroscope). For each channel, you have the header, data, and check sum information. Compute the number of bits per second and multiply with six. Then, show that the total rate is less than bluetooth max capacity. I hope this helps. $\endgroup$
    – Maxtron
    Commented Sep 2, 2019 at 17:09
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    $\begingroup$ If the rate is writen-in-stone, it was very likely set by NASA in the mid 60s. $\endgroup$
    – user28715
    Commented Sep 2, 2019 at 20:39

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One random thought, the 125-Hz sampling frequency allows the use of notch filters to cancel 50-Hz and 60-Hz periodic powerline noise ? It would be possible to cancel this periodic noise in hardware but it would cost more, it would be harder to integrate in wearables (large capacitor values), etc. ...

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I'm not sure I can state anything better than Marcus's or Maxtron's comments (it's that way because it's always been that way / because the hardware is limited to that rate), but another way to think about it is:

  • The Nyquist rate is 62.5 (=125/2) Hz.
  • Can your acceleration or rotational angles (the things measured by the accelerometer and gyroscope) change at a frequency faster than that?

If your instrumented system cannot, then this sampling rate is OK. If your system can move faster, then the sampling will miss something.

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