"Crucifixus Etiam" by Walter M. Miller, Jr.
From the story:
Breathing was unnecessary, except to provide wind for talking, but Manue breathed in desperate gulps of 4.0 psi Martian air; for he had seen the wasted, atrophied chests of the men who had served four or five years, and he knew that when they returned to Earth-if ever-they would still need the auxiliary oxygenator equipment.
According to this summary:
Desperate to find some sort of meaning for the work he is doing, Manue goes to one of the “troffies (for atrophy, the older workers who have given up any hope of returning to Earth), who explains it to him as a problem of overproduction and underconsumption.
We see here the essential elements of Mars, atrophied lungs, and of course the unique word “troffie.”