I read somewhere (lost to the fickle beasts of memory and time, of course) that rowing and the like is not particularly effective, precisely because it requires big, slow movements against resistance, which the human body is not that efficient at[1]. What we are efficient at is quick, light, repetitive movements – like pedaling with the proper gear selected. This is why Ivan Illich phrased it as the bicycle being "the perfect transducer to match man's metabolic energy to the impedance of locomotion".

[1]: This is also why rowing and weightlifting are such a good type of exercise to get stronger, and why bicycling requires that you put in a lot of hours to get stronger from it.