Normally, a body should posses its natural energy, (mc^2)/2. Any change in its energy will create a potential state in the body. That is, the body resists the change, and so it becomes impossible to increase/reduce the energy further.

Half of the natural energy remains inside the atoms as potential energy. The rest remains partly as vibrations etc, of atoms/molecules, and the rest as speed of the body. The maximum speed that a body (made up of atoms/molecules) can attain is 0.6c (based on my model). However, I cannot arrive at a minimum speed from my model. It may be noted that we are now moving at a speed close to 0.33c as per my model.