Exercise is known to have considerable psychological effects. It can raise moods, for example, and expand people’s sense of what they are capable of doing. So perhaps, the researchers speculated, exercise might alter how well people can control their impulses.
To find out, the scientists decided first to mount a tiny pilot study, involving only four men and women.
These volunteers, who had been sedentary and overweight, were told they would be taking part in an exercise program to get them ready to complete a 5K race, and that the study would examine some of the effects of the training, including psychological impacts.
The volunteers began by completing a number of questionnaires, including one that quantified their “delay discounting,” a measure that psychologists use to assess someone’s ability to put off pleasures now for greater enjoyments in the future. It tests, for instance, whether a person would choose to accept $5 today or $15 a week from now.
The delay-discounting questionnaire is generally accepted in research circles as a valid measure of someone’s self-control.
The volunteers then undertook a two-month walking and jogging regimen, meeting three times a week for 45 minutes with the researchers, who coached them through the sessions, urging them to maintain a pace that felt difficult but sustainable. Each week the men and women also repeated the questionnaires.
Finally, a month after the formal training had ended, the volunteers returned to the university for one more round of testing. (Later, two of them also ran 5K races.)
The results were intriguing, the researchers felt. Three of the four participants had developed significantly greater self-control, according to their delay-discounting answers, and maintained those gains a month after the formal training had ended. But one volunteer, who had missed multiple sessions, showed no changes in impulsivity.
A four-person study is too small to be meaningful, though, so the researchers next repeated the experiment with 12 women of varying ages, weights and fitness levels.
The results were almost identical to those in the pilot study. Most of the women gained a notable degree of self-control, based on their questionnaires, after completing the walking and jogging program. (In this experiment, they were told they were training for better fitness.)
But the increases were proportional; the more sessions a woman attended or the more her average…