View Full Version : newbie about emg & rms

02-08-2004, 06:18 PM

I'm a Ph.D. student working on an exo-skeleton project and I'm new to the
field of biomechanics and emg-signals.
When recording emg-signals and post-processing them with the rms-formula, I
get quite strange results sometimes (they can also be seen in the original
signal): When the observed muscle _seems_ to be contracted with the same
force over a few seconds (like holding up your thigh in a certain angle) the
rms value changes significantly over time nonetheless (going up and down with
a frequency of a few Hz, but the leg does not move very much).
Why is this the case?
Is it that other parts (other motor units) of the _same_ muscle are getting
activated/deactivated (and I don't get the signal from them), so that the
resulting output force remains "constant"? Or is it rather that other
_muscles_ are getting activated/deactivated supporting the muscle under

Any help / pointers would be appreciated!
Best regards,
Christian Fleischer

Dipl.-Ing. Christian Fleischer
Technical University of Berlin
Computer Engineering and Microelectronics
Sekr. EN 10 - Einsteinufer 17 - 10587 Berlin - Germany
Fon:+49 (0)30 314-73114 - mailto:fleischer@cs.tu-berlin.de
Fax:+49 (0)30 314-21116

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