Physically active people are biologically younger than the couch potatoes, a study published Monday in the Archives of Internal Medicine has found.

A long-term health study based on 2,401 twins found that those who had an active lifestyle appeared to be as much as ten years younger biologically than those of the more sedentary ones.

The researchers extracted DNA from the participants' white blood cells and examined the chromosomes to determine the length of a genetic sequence called telomeres, which were found at the ends of chromosomes.

Telomeres get shorter when a cell divides. When telomeres get too short, cells stop dividing. Aging occurs as more and more cells reach the end of their telomeres and die.

The study suggested the moderately active subjects who averaged 100 minutes of physical activity a week had telomeres that on average looked five or six years younger than the least active subjects who averaged 16 minutes a week. Those who did the most -- doing 199 minutes on average a week had telomeres that appeared to be about nine to ten years younger than those who did the least.