In the late 1940โs and early 1950โs, British researchers compared drivers and conductors on Londonโs double-decker buses.ย ย Their demographics were virtually identical: men, same ages, from same backgrounds, same incomes, same amount of smoking and drinking โ the only difference was the conductors walked up and down aisles and stairs all day, while the drivers sat.ย And the drivers had lots more heart attacks!