Gripping things hard needs energy even though nothing really moves. So I think we could harvest energy from this action, but I know that any type of energy harvesting requires moving parts.
So can we mechanically, chemically or quantum-mechanically harvest energy from constant gripping?
Have a look at the answers to Why does holding something up cost energy while no work is being done?.
Gripping things takes energy not because a constant, stationary force does any work but because of the way muscles work.
A stationary force doesn't do any work so no energy can be harvested from it. The best you could do is capture the heat given off from your muscles as you hold grip. However this is unlikely to be a useful source of energy.
No, gripping something with your hands will make you feel tired because that is how muscles work: blood is pumping, cells are working...
But imagin the gripped object on a table, and on it a pile of heavy books. The effect on the object is the same (more or less) than when you grip it with your hand, but the books never get tired.
You could harvers energy from pressure, but you have to give something in return, so that the laws of conservation are kept. For example, you can get energy from deformation of a crystal lattice. See the piezoelectric effect for details.
