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Sorry if it has been asked before I am sure. Anyways, if I hold a ball in the air, I do no work but I do spend energy ("chemical", heat... whatever happens in my muscle) and get tired. Where does the energy or whatever to cause me to get tired come from? For example how is an electrical charge capable to pull forever and never get "tired"?

sammy gerbil
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paradox
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This article explains well the mechanism of the skeletal muscles. Even though you don't see macroscopic movement and you expect your power "output" to be zero, because $\boldsymbol{P = F\cdot V}$ There is actually movement in your muscles.

K. Kirilov
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