Did you look at the Oscillator script?  Might be the best choice for
overall constant sinusoidal shaking.  

The tricky part is finding exactly which muscles to vibrate, and when the
shakes get big, you'll need to compensate as well.

The body automatically compensates for big moves to keep itself upright.  
So you'd have to apply the oscillation to Right Shin Bend in one direction, 
then take the same oscillation to Right Thigh Bend and Right Foot Bend 
in the opposite way.  

Might take some self-observation to find the exact patterns
of these compensations.

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