The human back wasn't made to be in a sitting position for hours on end. I was taught to use my left foot on the peddle. This from a physio. Felt a little strange at first but I don't even think of it unless someone mentions it. Lots of breaks away from the machine, the right height table, the correct chair and sitting in the chair not perched on the edge.
I'm no expert and when I was young sat in some peculiar positions and sewed for hours even when my back was burning. Did my back no favours.