Our exercise habits may influence our sense of purpose in life and our sense of purpose may affect how much we exercise, according to an interesting new study of the reciprocal effects of feeling your life has meaning and being often in motion. The study, which involved more than 18,000 middle-aged and older men and women, found that those with the most stalwart sense of purpose at the start were the most likely to become active over time, and vice versa. The findings underscore how braided the relationship between physical activity and psychological well-being can be, and how the effects often run both ways.