The body’s response to a chemical found in the brain, orexin A, may be linked with the desire to exercise and may explain a difference between active people who are always on the go and couch potatoes. Research published in the American Journal of Physiology – Regulatory, Integrative and Comparative Physiology, online August 14, 2006, studied the response of rats to orexin A. Rats who were lean and fidgeted a lot were very sensitive to orexin A, while sedentary rats were not.

People who engage in spontaneous activity, who tend to be active during the day tend to be leaner than those who vegetate in front of the television. The researchers wanted to see if there was a chemical cause for the tendency to be active. They focused on orexin A because it is known to be involved with appetite as well as movement.

The researchers took rats who had a tendency to be obese and rats who were lean and treated them with orexin A. Rats who are prone to be obese are not very sensitive to orexin A and did not respond to injections of the chemical. Lean, active rats are very sensitive to the orexin A and became even more active when injected with the chemical.