People not interested in exercising tend to be docile in disposition

While commenting on the research study findings, lead researchers Dr. Peter Biro from University of New South Wales, Australia, said in a press statement:

“Some of us are couch potatoes while others are drawn to sport and exercise. We often associate the athletic 'jock' type or person with being aggressive and social, whereas the more sedentary 'nerd' often is seen as more socially awkward and submissive.”

He added though, "these are generalizations, but most people would probably agree there is some truth to them. If so, why should individuals differ in their propensity for activity and in their personality, and why might they be related?"

Metabolism rate decides behavior
Study researchers also noted that these findings might be enough to prove a link between individual’s personality type and the capacity at which he/she generates energy (metabolism), in turn intensifying diverse behaviors.

They suggested that people with high metabolism tend to be more aggressive and dominating as compared to people with low rate of metabolism.

"It may just be that some individuals generate much more energy than others and when those individuals are captive with abundant food, they must outlet 'excess' energy that is normally expressed in nature in activities such as feeding and defense of food supplies etc,” noted Dr. Biro in the research report.

Captive animals too exercise
Researchers noted in their report that there are many animals that spend considerable amount of time exercising or engaging in physically demanding activities even when they are in captivity.

"Animals in captivity often engage in energetically demanding behavior when they have unlimited food available. Mice spend considerable time on running wheels, for example, and other animals often pace back and forth in zoo enclosures.

Given they don't need to move about in search of food as they would in nature, we might ask why they are apparently 'exercising'," wrote study researchers.

They might have high rate of metabolism and probably need to do something to spend the energy generated.

Dr. Biro concluded that even after this study more research needs to be done to get the “really solid understanding of the links between metabolism and personality in animals, but recent research suggests these ideas have merit and are worth studying further."

The study findings recently appeared in the journal 'Trends in Ecology and Evolution.'