Davis and celebrity trainer Brad Kolowich, Jr. But a growing body of research shows it may have another, more surprising effect: In men, regular exercise appears to be a natural Viagra.
In one study, sedentary middle-aged men assigned to participate in a vigorous exercise program for nine months reported more frequent sexual activity, improved sexual function, and greater satisfaction. Those whose fitness levels increased most saw the biggest improvements in their sex lives. Research in women has found that those who are physically active report greater sexual desire, arousal, and satisfaction than women who are sedentary. In one unusual experiment, young women who did intense cycling for 20 minutes and watched an X-rated film showed greater physiological sexual arousal as measured by a device that assesses vaginal blood flow than subjects who did not exercise before seeing the film.
Increased blood flow helps explain why exercise leads to better sexual function in men as well. An enhanced self-image from exercise may play a role too. Men and women who exercise may be more likely to feel sexually desirable, which can lead to better sex. So can greater strength, flexibility, and stamina that result from exercise.
In addition, physical activity—especially strength training—can increase levels of testosterone, which may boost sex drive in men and women. However, overtraining can have the opposite effect by lowering testosterone levels. Indeed, a recent study found that that men who do very vigorous exercise on a regular basis tend to have lower libidos.
There were no differences in test results. But much remains unknown, including whether women are affected differently than men. Men burned more than women. The level of intensity was considered moderate, comparable to that of walking or doubles tennis. For most people, however, sex doesn't last as long as those other activities, which means it burns fewer calories overall. In the aforementioned study, when sexual activity was compared to a minute, moderately intense workout on a treadmill, the treadmill burned about three times more calories.
But sexual activity did come out ahead in one measure: Adapted from Fitter Faster: Davis with Brad Kolowich, Jr.