As a rower myself I wanted to type the same correction initially, but then realized that the parent comment is probably referring to a rowboat rather than a racing shell. No sliding seat, no leg drive.

Rowing in a real rowboat has little to do with the legs: the seat is fixed. It has a lot to do with the back, however.

"Rowing machines" have very little to do with real rowboats. Real rowboats don't have sliding seats.