“You might imagine that an exercise regimen would have to be pretty grueling to be effective against depression. Maybe hours of running every day? Or some kind of strenuous weight lifting—the kind that makes people’s neck veins bulge? Incredibly, however, Blumenthal simply had his patients take a brisk half-hour walk three times a week. That’s it. And yet this remarkably low “dose” of exercise proved to be more effective than the Zoloft.”