NEW YORK (Reuters Health) — Willpower is a lot like muscle strength, a new study suggests — some of us have more of it than others. And while people may be born with an innate capacity for self-regulation, we can probably all take steps to boost our willpower, Dr. Suzanne C. Segerstrom of the University of Kentucky in Lexington told Reuters Health.Segerstrom and her colleague Dr. Lise Solberg Nes hypothesised that a person’s heart-rate variability — the capacity of the heart to be sensitive and responsive to changing demands — could serve as a stand-in for self-regulatory strength.

Heart-rate variability is controlled by the parasympathetic nervous system, which acts as a brake for the sympathetic nervous system, which is responsible for triggering the “fight or flight” response.

Segerstrom and Nes had 168 university students fast for three hours, and then presented them with a plate of carrots, warm chocolate chip cookies, and chocolate candies.

Some were instructed to eat the cookies and candies only, while others were told to eat only the carrots. Afterwards, study participants tried to solve a series of anagrams, some of which were unsolvable.

Heart-rate variability increased more among the students eating the carrots than among those eating cookies and candies, suggesting they were giving their self-regulatory “muscle” a workout. And those told to eat carrots gave up faster on the anagram puzzles than students who ate cookies and candies, suggesting that they had used up more of their self-regulatory strength during the food task.

People who showed the greatest heart rate variability at the study’s outset also persisted the longest on the anagrams.

While our muscles let us know when fatigue sets in, we don’t get a warning when our self-regulatory strength is petering out, Segerstrom noted. It’s not likely that average people will start going around with heart rate monitors to gauge their vulnerability to temptation, she added, but such an approach could be helpful to people with serious problems of self-regulation, for example alcoholics or cigarette smokers.

It’s possible that people might be able to strengthen their self-regulatory “muscle” with physical exercise-which offers a “double whammy” because it increases the fitness of the heart muscle and also works out the brain by forcing people to do something that they don’t necessarily want to keep doing, Segerstrom said.

Studies have shown, she pointed out, that repeatedly employing “effortful self-regulation” can indeed strengthen willpower. “In a way it is kind of like a muscle, in that the more you work it the stronger it gets.”