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FIRST, AT LAST Jeannette Seckinger of Somerville, Mass., sprinted past Elena Orlova, who lives in Gaithersburg, in the final 200 meters to capture the women's segment of the SunTrust National Marathon on Saturday.

In every race I run, I always manage to end up just behind my arch nemesis. It doesn't matter that I've never met this person before. Nor that this person knows absolutely nothing about our intense feud. Nor that it's a different person each time. All I know is I'm not letting Ms. Purple Shorts get to the finish line before me.

According to Ed Acevedo, president of the American Psychological Association's division of exercise and sports psychology, that behavior doesn't make me crazy. It makes me human.

"They say the difference between a jogger and a runner is an entry form," he says. "It's the competition that keeps you motivated to train."

What gets that adrenaline pumping is not some abstract goal of improving strength, but the immediate thrill of tackling opponents, swiping the ball, scoring -- and risking a bloody nose along the way.

So competition is awesome, right? Except when it's not,

The problem becomes the person who feels hostility in comparing themselves to other people,"