myoelectric prosthesis
/ MY-oh-ee-LEK-trik /
When you decide to make a fist, your brain sends a signal down nerves to your forearm muscles, and as those muscles contract they give off a tiny electrical flicker. A myoelectric prosthesis is built on a clever idea: place sensors on the skin over the residual muscles, detect that electrical flicker when the person tries to move, and use it as a switch to drive small motors that open and close an artificial hand. The person 'thinks' about moving the muscle, and the motorised hand responds.
In practice, electrodes sit inside the socket against the skin over two muscle groups in the residual forearm. Tensing one muscle (as if making a fist) tells the hand to close; tensing the other (as if opening the hand) tells it to open; how hard the person tenses can control how fast or how strongly it grips. This is what the popular term 'bionic hand' refers to. The appeal is real: no shoulder harness and cable are needed, the grip can be stronger than a body-powered device, and the hand looks and moves more naturally. Advanced multi-articulating hands can even form several different grip patterns.
The honest balance sheet matters. Myoelectric hands are heavier, far more expensive, need daily recharging, dislike water and sweat, and require real training to control reliably. Crucially, like every prosthetic hand they give no sensation — the user still grips blind and must watch the hand. Control can also be unreliable when the muscles are sweaty or fatigued. For all these reasons, plenty of users still prefer a simple, rugged body-powered hook for daily work and reserve the myoelectric hand for tasks or settings where its appearance and grip strength earn their keep.
A myoelectric-hand user lightly tenses the muscles on the top of her forearm, as if straightening her fingers, and the motorised hand opens; she relaxes and gently tenses the underside muscle, and the hand closes around a coffee mug — all without any harness, but she must watch to judge how hard it is gripping.
Muscle signals switch the motors on and off — but the hand still cannot feel its own grip.
The marketing word 'bionic' oversells these hands: they are clever motorised grippers controlled by muscle signals, not living hands — they have no sensation, need charging, and can fail when muscles are sweaty or tired.