There may be a link between aspects of an individual's personality and their capacity to exercise or generate energy, a new study has suggested.
Humans are not the only animals that choose to exercise and individuals within the same species differ in their levels of activity, said Peter Biro, a senior lecturer in the UNSW Evolution and Ecology Research Centre with colleague Judy Stamps of the University of California.
Scientists recognise that many animals have 'personality', in that they display consistent differences in behaviours.
Biro said it is significant that those behaviours often relate to the rates at which they acquire and expend energy through feeding or activity.
"Some of us are couch potatoes while others are drawn to sport and exercise," Biro said.
"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
"These are generalisations, 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? ," said Biro.
The study has concluded that there is enough evidence to suggest a link between an individual's personality and the rate of its metabolism - the chemical process that converts food into the energy that fuels the body.
"Animals in captivity often engage in energetically demanding behaviour 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'.
"Recent research suggests that this behaviour might be related to an individual's capacity to generate energy - its 'metabolic capacity'. For example, mice in isolation that have high metabolism tend spend more time on running wheels, and run faster, than those with low metabolism.
"Male crickets with sex on their mind tend to call to attract mates more and have higher metabolism than those with slower metabolism," said Biro.
The findings were published in the journal Trends in Ecology and Evolution.