The least-fit segment of the United States has twice the mortality risk of even those who are just a bit more in shape, according to a study recently published in the official journal of the American College of Sports Medicine.

A research team from Stanford University led by Victor F. Froelicher, M.D., and Jonathan Myers, Ph.D., performed exercise tests and followed more than 4,300 subjects from 1986 to 2006, none of whom had a history of heart disease. Fitness and physical activity levels were measured using treadmill tests and questionnaires, and mortality rates were tracked during the 20-year study period.

Sandra Mandic, Ph.D., and the research team from Stanford analyzed the results, and found that the mortality rate for the least fit individuals was twice that of the second least fit group, and more than four times the rate of the most fit group.

Fitness was the strongest predictor of mortality in this group of healthy individuals.

The study suggests that reduced recent physical activity, rather than differences in health status, contributes to the striking difference in mortality rates between the least-fit individuals and those who are just a bit more fit.

Nearly two-thirds of the least-fit individuals were not meeting the minimum recommended amount of physical activity (at least 150 minutes per week, or 30 minutes per day five days per week). Yet, this group achieves the greatest health benefits from increasing fitness.