During an experiment, it was found that an 80.0 kg man lost 0.260 kg of body fat having an energy content of 33.1 MJ/kg by lifting one 50.0 kg mass from the floor to a 1.50 m high shelf every 5.00 seconds continuously for 4.00 hours.
Ignoring respiratory and perspiration losses, determine the energy conversion efficiency of the muscular contractions.