[TrevorJ]

As has been pointed out, the comparisons are only useful pertaining to the same brain before regular exercise is present and after. You can't glean much from comparing one person to another because baseline intelligence varies too much to account for.

Now, what you are describing may be a case of self-selection. It may be possible (though I do not concede this point) that smarter people tend to gravitate toward the more oddball sports. That doesn't indicate that sprinting does not benefit the brain. Here's a thought experiment:

There are 100 people at the pool and 50 life jackets. People are allowed to choose to use a jacket or not, until all jackets are gone. You may find that better swimmers on average choose not to use a jacket. That does not indicate that the life jacket is not useful for swimming.

[rdouble]

Sure, whatever. The original point about your brain moving faster to keep up with your feet is stupid in any context. There's countless techniques in nearly every athletic sport about how to shut your brain down so that only your muscles and autonomic nervous system are doing the work. Athletic speed has no effect on other forms of intelligence. If anything it has a negative effect because sprinting is anaerobic and therefore is cutting off oxygen to your brain. I have no idea what you're getting at with the life jackets.

[TrevorJ]

It's tough to use intuition to bring any real insight to bear on biological systems, I'd be really interested in finding some real research into the matter.

Re: the lifejackets I was demonstrating that the effectiveness of the jackets is not effected by who chooses to use them. I was pointing out that saying less intelligent people gravitate towards sprinting does not prove that sprinting has no positive benefits on intelligence.