Indeed, when I was given a backseat trip in an F3, admittedly not the most agile of chariots I came out wringing with sweat and knackered and I was a fit tubby little prop. The driver up front climbed out with only a mild sheen on his brow. What I remember most was while I was fighting the g and grunting like a pig he was chatting normally.
Fit for purpose - definately, ever been inside a gym - probably not, a runner - absolutely not.