For those who have not seen the cartoon, here's a short preamble: Bluto feigns sickness to get out of doing work on the battleship and ends up in the hospital. Popeye catches Bluto in his sham, and after setting his mouth ablaze, gives chase to Bluto through the hospital. The following chain of events start when Bluto runs into a steam room to escape from Popeye.
Here's some cartoon logic and cartoon physics at work -
Popeye shuts Bluto in a steam room and Bluto shrinks. Take away mass.
Popeye inflates Bluto with oxygen to return him to normal size. Add mass.
Bluto has a mishap with a rain cloud and his inflated body is burst like a balloon by lightning - his deflated body falls to Earth. Take away mass.
A husk that needs to be filled + the need to get Bluto back to work….
… calls for Popeye to pump Bluto full of spinach. Only an industrial sized can will fill the space left by the escaped air. Add mass + strength.
Bluto, full and powered = ready to work. It all makes sense.
Cartoon logic in action: