We've all had the experience of being in an exercise rut. After being slothful for a couple of days (or weeks, or months, or years), it becomes ever harder to motivate yourself to get your butt off the couch.

But new science suggests that lack of exercise doesn't just transform your energy levels and your muscle tone, making it harder to move as much as you know you should. It may actually also transform your personality in ways that not only make it harder to exercise, but also to accomplish whatever else you need to do to be successful in life.

Sloth is a success killer.

Everyone knows sitting around all day is bad for your health, but to determine how inactivity affects personality, a team of French researchers analyzed data on over 9,000 volunteers covering 20 years. They examined both how sedentary the subjects were and how their personalities changed over time, looking for correlations. They found some.

The study, "found that subjects who reported being less active had greater reductions on average in conscientiousness, openness, agreeableness, and extroversion--four of the so-called Big Five personality traits--even after accounting for differences in baseline personality and health. No link was found with the fifth trait, neuroticism," reports Scientific American.

While further research is needed, these findings confirm the results of earlier studies that show personality changes more over the course of your life than many people believe. And it adds the insight that, over time, your sedentary lifestyle will likely nudge you to become less open to new experiences, less hard working, and less sociable. This is bad news if you're looking to get ahead in life.

More conscientious people are more successful. 

While the relationship between agreeableness and success is complicated (some older men in leadership roles seem to do better if they're less agreeable), the link between conscientiousness and success, in business and in other domains, is strong.

"There's a staggering amount of research linking conscientiousness with success. A National Institute of Mental Health study found that conscientious men earn higher salaries. The National Institute on Aging also found that conscientiousness is linked to income and job satisfaction. Other studies show that conscientiousness is the most important factor for finding and retaining employment," reports Drake Baer on Business Insider. "People who test high in conscientiousness get better grades in school and college, commit fewer crimes, and stay married longer. They live longer too."

Exercise already had a long list of benefits--from improved health to reduced stress and  enhanced cognition. It's emerging it may also have another. Not only does your personality shape your willingness to exercise, but it's looking like your willingness to exercise shapes your personality. And if you want the sort of personality that will make you more successful, you should probably get off your couch.