When holding weight, such as a school bag, no mechanical work is done because work is defined as the product of force and displacement, and there is no displacement while holding the weight. Although energy is expended by skeletal muscles to maintain the force, this does not equate to work being done on the object. Muscles experience fatigue due to energy consumption, but this is a different concept from performing work on the weight itself. The discussion highlights the distinction between work done "on" an object and work done "by" muscles, emphasizing that while muscles may exert force, they do not accomplish work without displacement. Ultimately, the energy used by muscles to hold weight does not translate into mechanical work in the physics sense.