February 07, 2014

Surface EMG from Thumb: Strongly 'Opposed' ?

Lead placement for the experiment, as shown on the right.
As I have already mentioned, the ground electrode sits atop
the manubrium sterni, on the upper chest (breastbone).

The camera recording is shown below. You can see the Piezoelectric crystal's spark and also hear its sound on snapping. However, I haven't yet had time to analyze if the spark did contribute some 'useful' static on the trace (open & watch this .wav file in BYB software).

Method: Pressing on a piezo crytal (from a cigarette lighter) by 'opposing' the thumb against the base of the little finger (as shown by the figure). Electrode placement shown in red & green markings [the ground electrode sits atop manubrium sterni]. Muscle (mainly) contracting is "opponens pollicis", a small, triangular muscle in the hand, which functions to oppose the thumb. [Strictly speaking, opposition of the thumb refers to the tip of the thumb touching the tips of other fingers. But that way, generating enough force without creating an unnecessary torque that topples the piezo is quite a challenge! After all, I had no assistant, and had to hold the camera too with the other hand]

Concept: A fixed and constant amount of force is necessary each time before the spring yields and the piezo fires. This end point is supposed to be caught in the trace 1) as a sharp spike after the surface EMG pattern or, 2) can be 'used' as a 'static'.

EMG amplitude and rate of spikes will need to be analyzed in short, discrete time intervals by simple counting.

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