Self-control is like a muscle, and just like a muscle, it tires through use and needs to be strengthened or replenished, suggests a study by psychologist Roy F. Baumeister, PhD, Eppes Professor of Psychology at Florida State University.

The study--which appears in Alcoholism: Clinical and Experimental Research (Vol. 27, No. 2)--tested three theories on self-control. One theory treats self-control as a cognitive process, one as a learned skill and another as a behavior that requires willpower. Through a series of experiments with 800 participants, Baumeister used the theories to investigate the levels of energy required for exercising self-control and resisting temptation.

The results from the experiments favored the idea that self-control requires willpower--in which people use energy and strength to overcome a temptation--compared with the other two theories. Baumeister theorizes that when willpower gets tapped out, a person can become vulnerable to impulsive behaviors, such as alcohol abuse.

For example, in one of his experiments, participants who had skipped a meal were tempted with freshly baked cookies and chocolates. Some participants were instructed to resist the treats and instead eat radishes. They were then asked to complete an unsolvable geometric puzzle. Those who resisted the treats tended to give up faster on the puzzle than participants who were allowed to indulge in the temptation or who had not been tempted with any food. Baumeister believes that they gave up faster because they'd already expended energy exercising self-control.

A similar pattern emerged in another experiment in which participants were instructed to control their emotional responses--by stifling or amplifying their reactions--as they viewed an upsetting video. The researchers then gauged their physical stamina by testing how long they could squeeze a handgrip device. Participants who controlled their emotions tended to give up faster on the task compared with those who did not have to suppress or control their emotions while watching the video.

Based on these findings, Baumeister says the research might help explain why some people are more vulnerable than others to substance abuse relapse. Their energy, he says, might have been used elsewhere--in stress-management, for example.

How then can people restore their self-control? Baumeister says further analysis is under way, but evidence has so far supported sleep and positive emotional experiences, such as humor and laughter, in helping to restore self-control.

"Self-control is one of the most powerful, beneficial and adaptive traits in human nature," he says.

--M. DITTMANN