A device implanted in the palm of the hand controls the grip of patients using artificial limbs.
Gripping too tightly causes muscle tiredness, while holding too lightly can cause them to drop it.
But the new implant, developed by the Center for Sensory-Motor Interaction at Aalborg University, in Denmark, monitors bundles of nerves in the index finger.
It detects overexertion and compensates by adjusting the grip.
Three electrodes are wrapped around a nerve bundle in the palm which feeds information on the strength of the grip back to a muscle stimulator, located externally on a wrist cuff.
The stimulator is controlled by two buttons pressed by a head-mounted prodder, one to turn the system on and increase the power, the other to decrease the power and turn the system off.
Artificial sensors embedded in gloves have previously been developed, but the device is the first to be implanted in the hand itself.
Successfully used
Nerve implants have been successfully used to control continence in paralysed people.
Patients are tempted to use the system at full power all the time, says researcher Morten Haugland, but this is unnecessary as, for instance, prodding a potato with a fork requires a strong grip but carrying it to your mouth does not.
"Our system makes sure you use the right amount of force," he said.
Ultimately, he hopes to fully restore sensation in patients with spinal injuries and similar electrodes are now being used to help paraplegics with their balance.
Simon Barnes at the Spinal Injuries Association in the UK said: "These developments are welcome because it maintains a better quality of life for paralysed people until we find treatments for spinal cord repair.
"Our one concern would be that some treatments of this kind used to be irreversible and would damage nerves that would be needed in the future, but this is no longer the case in all instances.
"This is a new technology that has a lot to offer paralysed people."