The story
From indoor + rowing. From being a stroking activity performed indoors.
Etymology from Wiktionary, CC BY-SA 4.0.
indoor rowing
Today it means: A disabled sport that simulates rowing and sculling using rowing machines linked up to create lanes and boats on an electronic course. Events may be against the clock, stroke count limited, or simulated course distances. Against the clock and stroke count limited disciplines use simulated distances for performance, while simulated course distances uses time of completion for performance. Full definition →