A Harvard study found that after a 12-week program of strength training, almost 90% of seriously depressed seniors no longer met the criteria for clinical depression. So lift your spirits by lifting weights! Bike riding for at least 20 minutes can also boost your body's natural levels of anandamide which can contribute to feelings of euphoria like those described by long-distance runners and cyclists. Penn State and Harvard researchers found that fitness predicts happiness better than finances. So get moving and get happy!!! Forget the bad day you had.