|MadSci Network: Biophysics|
For most activities, you'll be using both the extensors and the flexors. A crude way of looking at it is that the difference between extensor and flexor torque produces movement, and the sum of the torques produces stiffness.
As far as accuracy goes, part of that is going to involve the fluctuation in muscle force compared to the average force. Think of holding a ruler and shaking it. Small motions near your hand are going to result in large motions away from your hand. That's simple geometry. It suggests that force fluctuations in the shoulder are going to have greater effects on accuracy than fluctuations at the elbow or wrist.
When you write, do you use your whole arm? How much of the motion is with the wrist, how much with the elbow, and how much with the shoulder?
Now I have fairly poor handwriting, but my recollection is that good penmanship is based on the control of the muscles near the pen and paper.
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