Hello. When we are lifting up weight using arm, there is work done by us (we give energy for the weight to move upward and so we feel tired), and by law of conservation of energy, we can write mgΔh= mΔ(v^2)/2. However, when we are holding the weight statically (arm does not move at all), we also feel tired some time later. It seems like we are still consuming energy even when we do not have any work done on the weight and our muscle does not move at all. Why? How a contracted muscle that is static consumes energy? Non-living things that support weight does not need energy but living things does! Why? Your answer will be appreciated. Thanks!