Why we shiver/tremble/shake while performing some work which requires high accuracy?

Question

Shivering when nervous or anxious is a common thing.

But, shivering or trembling sometimes also occurs when we are performing a work which requires high accuracy. In such case, our whole body doesn't shivers but a part (usually hand) which is involved with that work shivers. The most common example is threading a needle. It requires great accuracy and you might have noticed that when you are doing so, your hands are continuously shaking which prevents you from accomplishing that task flawlessly. Even when we aren't in a state of nervousness, our hands tremble. It's un-resistable.

Yet another quick example - Try to stretch your one arm and try to keep it straight (have it loose, don't try to force it straight), you might notice that your arm is actually shaking a little bit. You can't hold it exactly straight without moving even a little bit.

It's also noticeable when we try to pin-point a small spot with our hand(finger) without actually touching it. (that finger and the hand as a whole starts trembling)

So, what's the reason? It isn't anxiousness as we shiver even when we are calm. Perhaps, it's gravity which is pulling our hand down and we are trying to lift it continuously which creates a imbalance? But, then we should shiver always?

Answer 1

If you thread needles often - like a dozen times a day for many days - you will eventually be steady as a rock, because practice improves the process (you will also unconsciously maneuver to steady both hands.) It's not inevitable that all people have involuntary muscle movements with very fine motor skills; it's a matter of ability/practice for most.

The steadying of larger muscle groups like the upper arms - especially against gravity - is less controllable (e.g. threading a needle with arms fully extended), but not even closely outside the realm of possibility. Think of what great athletes, dancers, craftsmen are able to do that is "impossible" for mere mortals.

Answer 2

Norepinephrine (noradrenalin) is a neurotransmitter and hormone released by the body in situations which, among other things, require focus. This may (partially) explain the shaking hands when focusing.

"The general function of norepinephrine is to mobilize the brain and body for action. Norepinephrine release is lowest during sleep, rises during wakefulness, and reaches much higher levels during situations of stress or danger, in the so-called fight-or-flight response. In the brain, norepinephrine increases arousal and alertness, promotes vigilance, enhances formation and retrieval of memory, and focuses attention; it also increases restlessness and anxiety."

The shaking occurs because the body is increasing burning of energy. There's not many good links online for this (unsurprisingly google searches of "noradrenalin shaking hands" pretty much only returns 'medical' websites trying to tell people they have a brain tumor), but I think what happens is the muscles twitch as a result of the excess energy release.

"When you suffer from anxiety, your body rushes with adrenaline - a hormone that gives your body a tremendous amount of energy, which - when unused - leads to physical agitation. That causes your hands and legs to shake, often visibly."

Beta-blockers are known to reduce symptoms of noradrenalin and are frequently (if questionably and irresponsibly) used to treat anxiety. We may shake less when we practice a process multiple times possibly because with practice anxiety associated with such tasks (I imagine a surgeon is quite nervous the first time they open up a patient) and the level of focus required (intricate tasks become easier with practice thus requiring less focus) both reduce, therefore reducing the amount of focus-related and anxiety-related physiological changes.