Interesting indeed! Responses are very interesting.
Infact I just wanted to know, 'Why do we feel tired while holding a weight in our hand or heads for a longer time?' It is probably very simple question and most of the people can alswer it. But I am just curious to know the actual causes and their impact in terms of law of physics. Is it (tiredness/loss of energy) due to body metabolism or the net impact of laws of force, energy and mass etc. How does it behave when the same weight is placed on a stand?