"Leaving Ferrari was a relief" —Kimi

If you limit it to GP cars yes but drivers back then drove many series, some of which required a lot of strength and stamina.
Not always obvious because few were as thin as today's crop.

 

Good call. I remember reading that Jody prepared for the hot races by doing push-ups and sit-ups in saunas/steam rooms.

 

Meanwhile Kimi prepares for races on the toilet!