[jiggy2011]

Intelligence and fitness are two very different things. Fitness has a lot to do with make up of muscle fibres in the body, fast twitch (anerobic) vs slow twitch (aerobic). This is why marathon runners and weight lifters have very different body types , training a lot in one discipline will make you worse at the other. Genetics plays a role in which type of muscle you can most easily develop.

Intelligence simply doesn't work the same way, learning to draw well won't make you worse at computer programming for example.

[lambdaphage]

Yes, maxing out one dimension of performance may degrade it in another. This is just Berkson, again. My point is that along the entire range of variation, all reasonable measures of athletic performance are likely to be positively correlated. If you doubt this, consider the following thought experiment:

1. Pick an arbitrary athletic contest: 100m dash, bench press, obstacle course, marathon, whatever.

2. You pick a member of the population at random.

3. I pick a member of the German national football team at random.

4. If Joe Schmoe wins, I pay you a dollar. If Dieter Schmieter wins, you pay me a dollar.

5. Repeat until convinced.

Who do you think will win more money in the long run? Will the Germans tend to win because of their high general fitness, or will it be a toss-up because the Germans merely have "high soccer fitness" which does not help (or perhaps even disadvantages) them at non-soccer tasks?

That is what I mean when I speak of a "general factor of fitness". Over the whole range of population, people who do better at one athletic task will tend to do better at any other. If you take a sample from the population, measure their performances on whatever athletic tasks you choose, and drop the results into PCA, you will find one factor which is positively correlated with every test and explains, I'm guessing, at least 3/4 of the variance. What happens at the extreme tails is already acknowledged, and does not bear on this general point.

I tried to find data for non-elite-athletes taking something like the NFL combine and couldn't find anything, but there, at least, is a testable prediction for you.

My only point about a "general factor of fitness" was that I am unfazed by the comparison to IQ, because physical fitness is a perfectly reasonable concept that captures something real in the world. So too IQ. If you think the analogy is inapt, remember who brought it up :)

[jiggy2011]

You're comparing a trained athlete against a person who is untrained. It is not surprising that fitness related tasks are very amenable to training in a way that is not quite so clear with intelligence. A more interesting comparison would be between a sedentary Dieter Schmieter who worked as a computer programmer (or a Dieter Schmieter who had trained purely for strength) and a random member of the population who was trained by Dieter Schmieter's coach for 10 years.

Amongst the general untrained population you will see very large variance between performance on different fitness tests. Lots of broadly built overweight people who are very strong despite never having done any weight training but can't walk up a flight of stairs without breaking a sweat and skinny people who can run well without much training but barely lift anything. So I would doubt that there would be a strong general factor for physical tasks.