WATERTOWN — British playwright Duncan Macmillan’s 2011 drama “Lungs” seems as simple as, well, breathing. It’s to be performed, Macmillan writes, “on a bare stage. There is no scenery, no furniture, no props and no mime. There are no costume changes.” What there is is a couple, M and W, who spend the entire 85 minutes of this intermissionless work talking to, and at, each other. That’s not a lot to work with, but in the New Repertory Theatre production now up in the Black Box at the Arsenal Center for the Arts, director Bridget Kathleen O’Leary and actors Nael Nacer and Liz Hayes manage well enough.

At first, the topic is whether to have a baby, and along with the usual concerns, M and W start asking whether they should be adding to the “seven billion people or so” already in the world. W has a possible solution: “We could work out the carbon footprint of the expanding nappies in the landfill and the Baby Gap hoodies flown in from the Congo or wherever and we could plant trees, entire forests, make something pure and and and oxygenating, so . . . ” So “Lungs” is about saving the planet and ensuring that future generations have air to breathe, but it’s also about lung power. At one point, W has a single sentence that covers almost a page of printed text.