"Runner's High": Is There a Limit?

I've sort of written about this before. But it's come up again, as I'm currently reading Off the Deep End, a tale of a 45-year-old man's quest to qualify for the 2008 Olympics (sound familiar)?

One chapter he writes focuses on the physiology of the act. Looking at the average age of Olympic swimmers, society scoffs at the thought that a man (or woman) in his (or her) 40s is capable of the Herculean feats, the incomprehensible times posted by the world's fastest.

The point he makes is that beyond talent, desire, training, motivation, and opportunity, older athletes must be able to overcome the brainwashing effect of society's (especially western society's) collective beliefs regarding age and aging.

And I have one friend who is intent on qualifying for the Boston Marathon. For her, it's not really a matter of if so much as it is when. Right now she runs around a 10:30/mile marathon pace. To qualify for Boston, she'll have to run for like 8:20. Boston may be somewhat elite, but with enough hard work, she plans to achieve it.

Both these situations are strongly resonant for me.

Because I've been wondering just how fast I can run. I don't run fast, now. Maybe I'll never run fast, taken as an absolute measurement ('cause let's face it: right now a sub-9:00 mile is fast for me).

But I have somehow been conditioned to think that my genetics hold me back. My legs are too short. My lungs aren't strong enough. My muscle fibers are all wrong.

In my mind, I've set a limit for myself, and am convinced that I am physiologically incapable of running any faster than, say, a 24:00 minute 5k.

But what if I'm wrong?

It comes down to a question of limits. Once upon a time, running a mile in under 4 minutes was impossible. Once upon a time, swimming a 200 m fly in under 2 minutes was impossible. Once upon a time, qualifying for the Olympic swim team past the age of 40 was impossible. And the inherent socialization of "4 minutes, 4 laps of a track, perfect"; "200 meters, 2 minutes, perfect" was a barrier that had to be overcome before those things could be done. Not only did talent and training and genetics and opportunity and conditions and motivation all have to come together for the athletes who busted through those barriers; they also had to contend with an inculcated sense of the impossible, that what they wanted to do--or what they suspected they could do--was beyond the realm of human possibility.

Those things have all been done. Which leaves me wondering:

Are there any limits? Or is it all in my head?

On a somewhat related note, I've decided that my best chance for qualifying for the Olympics someday is to take up Olympic weightlifting.