For example, more than 80 percent of the men who exercised two or three days a week view themselves as sexy, and all of the men who exercise six or seven days a week think they're sexy. But among those who work out four or five days a week, that percentage drops to 65.
Why the drop?
"I don't know," Penhollow says.
The study suggests it may have something to do with self-perception. Women who exercise four our five days a week, for example, were far less likely to rate themselves as physically attractive as those who worked out more or less.
What is clear, however, is those who think they're in poor physical shape also think they're not sexually attractive.
Some 60 percent of the males and 30 percent of the females who reported themselves as below average in fitness rated their sexual attractiveness as at least above average.
So Penhollow and Young say they've demonstrated that physical fitness really does play a role in our sex lives beyond the obvious gains of stamina and improved health. If we feel better about ourselves, we're more likely to regard ourselves as sexy.
However, it's worth remembering that this study consisted only of college students, and it's debatable as to whether they represent society as a whole, particularly when it comes to sex. Penhollow thinks they probably do, more or less, and the research she is conducting for her dissertation will extend to the general population.
Most of us probably think we already know the answer. But one function of science is to test the obvious. Sometimes, common sense is just dead wrong.
Lee Dye's column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.