Even in the more stereotypical physical things, there's always been a "loner" aspect for me, I guess. At my most physically active, I can remember playing basketball by myself for hours. Sometimes it'd be really offputting if other people came on to the court (yeah, even rain and cold weather was preferable lol..). I was in my head, but still active.
I don't think I'm a 5 though. Probably 6w5, like others here.
I think by my late teens/20s though, some shit went down where I asked different questions, did a lot of soul searching, thought and read about a lot about more things... I acted very much like a 5. I'm going to say that anything like that would bring out the "intellectual" side in an ISTP (or any SP, for that matter).