I don't know ... I found the limit of the speed at which I can crash on pavement without doing serious shoulder injury. Took me a couple attempts to dial it in, but I nailed it.

In unrelated news, I found a few of the limits beyond which physical exertion will cause near-unconsciousness and cause my heart to pause a while between beats. I haven't completely quantified that last one ... and I don't hope to.

I avoid mental limits by simply not thinking deeply.