I'm puzzled by this question regarding the work-energy prinple.
When a man holds a heavy weight in rest, he does not do any mechanical work to the weight, according to the work-energy principle. Then why does he consume much more energy in his body than the usually activity? It seems to me the comsumed extra energy must be mostly converted to the extra heat. According to the energy conservation principle, in maintaining the normal metabolism of the body, the chemical energy should be partially expended for cellular functioning, and partially converted to heat.
