To introduce the topic of mass deficit in physics, my teacher said that when he jumps he gains potential energy. So that energy, E, divided by c^2 gives him his increase in mass.
I am confused by this because surely the energy he ‘gains’ in gravitational potential comes from stored chemical energy in our body, so the overall energy of him stays the same. If anything work is done against the ground when we jump so we lose energy. Is my teacher right that we gain mass when we jump?